Lincoln Electric SVM151-A User Manual

SVM151-A

September, 2002

Safety Depends on You

Lincoln arc welding and cutting
equipment is designed and built
with safety in mind. However,
your overall safety can be in­creased by proper installation . . .
and thoughtful operation on
your part. DO NOT INSTALL,

OPERATE OR REPAIR THIS
EQUIPMENT WITHOUT
READING THIS MANUAL AND
THE SAFETY PRECAUTIONS
CONT AINED THROUGHOUT .

And, most importantly, think
before you act and be careful.

SERVICE MANUAL

For use with machines having Code Numbers: 10645

10736

Multi-Weld 350 Arc Converter

TM

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• Sales and Service through Subsidiaries and Distributors Worldwide •

Cleveland, Ohio 44117-1199 U.S.A. TEL: [phone] FAX: [phone] WEB SITE: www.lincolnelectric.com

• World's Leader in Welding and Cutting Products •

Copyright © 2000 Lincoln Global Inc.

i i

SAFETY

FOR ENGINE
powered equipment.

1.a. Turn the engine off before troubleshooting and maintenance
work unless the maintenance work requires it to be running.

____________________________________________________

1.b.Operate engines in open, well-ventilated
areas or vent the engine exhaust fumes
outdoors.

____________________________________________________

1.c. Do not add the fuel near an open flame weld-

ing arc or when the engine is running. Stop
the engine and allow it to cool before refuel­ing to prevent spilled fuel from vaporizing on
contact with hot engine parts and igniting. Do
not spill fuel when filling tank. If fuel is spilled,
wipe it up and do not start engine until fumes
have been eliminated.

____________________________________________________

1.d. Keep all equipment safety guards, covers

and devices in position and in good
repair.Keep hands, hair, clothing and tools
away from V-belts, gears, fans and all other
moving parts when starting, operating or
repairing equipment.

____________________________________________________

1.e. In some cases it may be necessary to remove safety
guards to perform required maintenance. Remove
guards only when necessary and replace them when the
maintenance requiring their removal is complete.
Always use the greatest care when working near moving
parts.

___________________________________________________

1.f. Do not put your hands near the engine fan. Do not attempt to
override the governor or idler by pushing on the throttle con­trol rods while the engine is running.

___________________________________________________

1.g. To prevent accidentally starting gasoline engines while
turning the engine or welding generator during maintenance
work, disconnect the spark plug wires, distributor cap or
magneto wire as appropriate.

ARC WELDING can be hazardous. PROTECT YOURSELF AND OTHERS FROM POSSIBLE SERIOUS INJURY OR DEATH.
KEEP CHILDREN AWAY. PACEMAKER WEARERS SHOULD CONSULT WITH THEIR DOCTOR BEFORE OPERATING.

Read and understand the following safety highlights. For additional safety information, it is strongly recommended that you
purchase a copy of “Safety in Welding & Cutting - ANSI Standard Z49.1” from the American Welding Society, P.O. Box 351040,
Miami, Florida 33135 or CSA Standard W117.2-1974. A Free copy of “Arc Welding Safety” booklet E205 is available from the
Lincoln Electric Company, 22801 St. Clair Avenue, Cleveland, Ohio 44117-1199.

BE SURE THAT ALL INSTALLATION, OPERATION, MAINTENANCE AND REPAIR PROCEDURES ARE
PERFORMED ONLY BY QUALIFIED INDIVIDUALS.

WARNING

Mar ‘95

ELECTRIC AND
MAGNETIC FIELDS
may be dangerous

2.a. Electric current flowing through any conductor causes
localized Electric and Magnetic Fields (EMF). Welding
current creates EMF fields around welding cables and
welding machines

2.b. EMF fields may interfere with some pacemakers, and
welders having a pacemaker should consult their physician
before welding.

2.c. Exposure to EMF fields in welding may have other health
effects which are now not known.

2.d. All welders should use the following procedures in order to
minimize exposure to EMF fields from the welding circuit:

2.d.1.

Route the electrode and work cables together - Secure
them with tape when possible.

2.d.2. Never coil the electrode lead around your body.

2.d.3. Do not place your body between the electrode and

work cables. If the electrode cable is on your right
side, the work cable should also be on your right side.

2.d.4. Connect the work cable to the workpiece as close as

possible to the area being welded.

2.d.5. Do not work next to welding power source.

1.h. To avoid scalding, do not remove the
radiator pressure cap when the engine is
hot.

CALIFORNIA PROPOSITION 65 WARNINGS

Diesel engine exhaust and some of its constituents
are known to the State of California to cause can­cer, birth defects, and other reproductive harm.

The engine exhaust from this product contains
chemicals known to the State of California to cause
cancer, birth defects, or other reproductive harm.

The Above For Diesel Engines

The Above For Gasoline Engines

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ii ii

SAFETY

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ARC RAYS can burn.

4.a. Use a shield with the proper filter and cover
plates to protect your eyes from sparks and
the rays of the arc when welding or observing
open arc welding. Headshield and filter lens
should conform to ANSI Z87. I standards.

4.b. Use suitable clothing made from durable flame-resistant
material to protect your skin and that of your helpers from
the arc rays.

4.c. Protect other nearby personnel with suitable, non-flammable
screening and/or warn them not to watch the arc nor expose
themselves to the arc rays or to hot spatter or metal.

ELECTRIC SHOCK can kill.

3.a. The electrode and work (or ground) circuits
are electrically “hot” when the welder is on.
Do not touch these “hot” parts with your bare
skin or wet clothing. Wear dry, hole-free
gloves to insulate hands.

3.b. Insulate yourself from work and ground using dry insulation.
Make certain the insulation is large enough to cover your full
area of physical contact with work and ground.

In addition to the normal safety precautions, if welding
must be performed under electrically hazardous
conditions (in damp locations or while wearing wet
clothing; on metal structures such as floors, gratings or
scaffolds; when in cramped positions such as sitting,
kneeling or lying, if there is a high risk of unavoidable or
accidental contact with the workpiece or ground) use
the following equipment:

• Semiautomatic DC Constant Voltage (Wire) Welder.

• DC Manual (Stick) Welder.

• AC Welder with Reduced Voltage Control.

3.c. In semiautomatic or automatic wire welding, the electrode,
electrode reel, welding head, nozzle or semiautomatic
welding gun are also electrically “hot”.

3.d. Always be sure the work cable makes a good electrical
connection with the metal being welded. The connection
should be as close as possible to the area being welded.

3.e. Ground the work or metal to be welded to a good electrical
(earth) ground.

3.f.

Maintain the electrode holder, work clamp, welding cable and
welding machine in good, safe operating condition. Replace
damaged insulation.

3.g. Never dip the electrode in water for cooling.

3.h. Never simultaneously touch electrically “hot” parts of
electrode holders connected to two welders because voltage
between the two can be the total of the open circuit voltage
of both welders.

3.i. When working above floor level, use a safety belt to protect
yourself from a fall should you get a shock.

3.j. Also see Items 6.c. and 8.

FUMES AND GASES
can be dangerous.

5.a.Welding may produce fumes and gases
hazardous to health. Avoid breathing these
fumes and gases.When welding, keep
your head out of the fume. Use enough
ventilation and/or exhaust at the arc to keep

fumes and gases away from the breathing zone. When

welding with electrodes which require special
ventilation such as stainless or hard facing (see
instructions on container or MSDS) or on lead or
cadmium plated steel and other metals or coatings
which produce highly toxic fumes, keep exposure as
low as possible and below Threshold Limit Values (TLV)
using local exhaust or mechanical ventilation. In
confined spaces or in some circumstances, outdoors, a
respirator may be required. Additional precautions are
also required when welding on galvanized steel.

5.b.

Do not weld in locations near chlorinated hydrocarbon

vapors
coming from degreasing, cleaning or spraying operations.
The heat and rays of the arc can react with solvent vapors

to
form phosgene, a highly toxic gas, and other irritating
products.

5.c. Shielding gases used for arc welding can displace air and
cause injury or death. Always use enough ventilation,
especially in confined areas, to insure breathing air is safe.

5.d. Read and understand the manufacturer’s instructions for this

equipment and the consumables to be used, including the
material safety data sheet (MSDS) and follow your
employer’s safety practices. MSDS forms are available from
your welding distributor or from the manufacturer.

5.e. Also see item 1.b.

Mar ‘95

iii iii

SAFETY

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FOR ELECTRICALLY
powered equipment.

8.a. Turn off input power using the disconnect
switch at the fuse box before working on
the equipment.

8.b. Install equipment in accordance with the U.S. National
Electrical Code, all local codes and the manufacturer’s
recommendations.

8.c. Ground the equipment in accordance with the U.S. National
Electrical Code and the manufacturer’s recommendations.

CYLINDER may explode
if damaged.

7.a. Use only compressed gas cylinders
containing the correct shielding gas for the
process used and properly operating
regulators designed for the gas and

pressure used. All hoses, fittings, etc. should be suitable for
the application and maintained in good condition.

7.b. Always keep cylinders in an upright position securely
chained to an undercarriage or fixed support.

7.c. Cylinders should be located:

•Away from areas where they may be struck or subjected to

physical damage.

• A safe distance from arc welding or cutting operations and

any other source of heat, sparks, or flame.

7.d. Never allow the electrode, electrode holder or any other
electrically “hot” parts to touch a cylinder.

7.e. Keep your head and face away from the cylinder valve outlet
when opening the cylinder valve.

7.f. Valve protection caps should always be in place and hand
tight except when the cylinder is in use or connected for
use.

7.g. Read and follow the instructions on compressed gas
cylinders, associated equipment, and CGA publication P-l,
“Precautions for Safe Handling of Compressed Gases in
Cylinders,” available from the Compressed Gas Association
1235 Jefferson Davis Highway, Arlington, VA 22202.

Mar ‘95

WELDING SPARKS can
cause fire or explosion.

6.a.

Remove fire hazards from the welding area.

If this is not possible, cover them to prevent

the welding sparks from starting a fire.

Remember that welding sparks and hot
materials from welding can easily go through small cracks
and openings to adjacent areas. Avoid welding near
hydraulic lines. Have a fire extinguisher readily available.

6.b. Where compressed gases are to be used at the job site,
special precautions should be used to prevent hazardous
situations. Refer to “Safety in Welding and Cutting” (ANSI
Standard Z49.1) and the operating information for the
equipment being used.

6.c. When not welding, make certain no part of the electrode
circuit is touching the work or ground. Accidental contact can
cause overheating and create a fire hazard.

6.d. Do not heat, cut or weld tanks, drums or containers until the
proper steps have been taken to insure that such procedures
will not cause flammable or toxic vapors from substances
inside. They can cause an explosion even

though

they have
been “cleaned”. For information, purchase “Recommended
Safe Practices for the

Preparation

for Welding and Cutting of
Containers and Piping That Have Held Hazardous
Substances”, AWS F4.1 from the American Welding Society

(see address above).

6.e. Vent hollow castings or containers before heating, cutting or
welding. They may explode.

6.f.

Sparks and spatter are thrown from the welding arc. Wear oil
free protective garments such as leather gloves, heavy shirt,
cuffless trousers, high shoes and a cap over your hair. Wear
ear plugs when welding out of position or in confined places.
Always wear safety glasses with side shields when in a
welding area.

6.g. Connect the work cable to the work as close to the welding
area as practical. Work cables connected to the building
framework or other locations away from the welding area
increase the possibility of the welding current passing
through lifting chains, crane cables or other alternate circuits.
This can create fire hazards or overheat lifting chains or
cables until they fail.

6.h. Also see item 1.c.

iv iv

SAFETY

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PRÉCAUTIONS DE SÛRETÉ

Pour votre propre protection lire et observer toutes les instructions
et les précautions de sûreté specifiques qui parraissent dans ce
manuel aussi bien que les précautions de sûreté générales suiv­antes:

Sûreté Pour Soudage A L’Arc

1. Protegez-vous contre la secousse électrique:

a. Les circuits à l’électrode et à la piéce sont sous tension

quand la machine à souder est en marche. Eviter toujours
tout contact entre les parties sous tension et la peau nue
ou les vétements mouillés. Porter des gants secs et sans
trous pour isoler les mains.

b. Faire trés attention de bien s’isoler de la masse quand on

soude dans des endroits humides, ou sur un plancher
metallique ou des grilles metalliques, principalement dans

les positions assis ou couché pour lesquelles une
grande partie du corps peut être en contact avec la
masse.

c. Maintenir le porte-électrode, la pince de masse, le câble

de soudage et la machine à souder en bon et sûr état
defonctionnement.

d. Ne jamais plonger le porte-électrode dans l’eau pour le

refroidir.

e. Ne jamais toucher simultanément les parties sous tension

des porte-électrodes connectés à deux machines à soud­er parce que la tension entre les deux pinces peut être le
total de la tension à vide des deux machines.

f. Si on utilise la machine à souder comme une source de

courant pour soudage semi-automatique, ces precautions
pour le porte-électrode s’applicuent aussi au pistolet de
soudage.

2. Dans le cas de travail au dessus du niveau du sol, se pro­téger contre les chutes dans le cas ou on recoit un choc. Ne
jamais enrouler le câble-électrode autour de n’importe quelle
partie du corps.

3. Un coup d’arc peut être plus sévère qu’un coup de soliel,
donc:

a. Utiliser un bon masque avec un verre filtrant approprié

ainsi qu’un verre blanc afin de se protéger les yeux du
rayonnement de l’arc et des projections quand on soude
ou quand on regarde l’arc.

b. Porter des vêtements convenables afin de protéger la

peau de soudeur et des aides contre le rayonnement de
l‘arc.

c. Protéger l’autre personnel travaillant à proximité au

soudage à l’aide d’écrans appropriés et non-inflamma­bles.

4. Des gouttes de laitier en fusion sont émises de l’arc de
soudage. Se protéger avec des vêtements de protection
libres de l’huile, tels que les gants en cuir, chemise épaisse,
pantalons sans revers, et chaussures montantes.

5. Toujours porter des lunettes de sécurité dans la zone de
soudage. Utiliser des lunettes avec écrans lateraux dans les
zones où l’on pique le laitier.

6. Eloigner les matériaux inflammables ou les recouvrir afin de
prévenir tout risque d’incendie dû aux étincelles.

7. Quand on ne soude pas, poser la pince à une endroit isolé
de la masse. Un court-circuit accidental peut provoquer un
échauffement et un risque d’incendie.

8. S’assurer que la masse est connectée le plus prés possible
de la zone de travail qu’il est pratique de le faire. Si on place
la masse sur la charpente de la construction ou d’autres
endroits éloignés de la zone de travail, on augmente le risque
de voir passer le courant de soudage par les chaines de lev­age, câbles de grue, ou autres circuits. Cela peut provoquer
des risques d’incendie ou d’echauffement des chaines et des
câbles jusqu’à ce qu’ils se rompent.

9. Assurer une ventilation suffisante dans la zone de soudage.
Ceci est particuliérement important pour le soudage de tôles
galvanisées plombées, ou cadmiées ou tout autre métal qui
produit des fumeés toxiques.

10. Ne pas souder en présence de vapeurs de chlore provenant
d’opérations de dégraissage, nettoyage ou pistolage. La
chaleur ou les rayons de l’arc peuvent réagir avec les
vapeurs du solvant pour produire du phosgéne (gas forte­ment toxique) ou autres produits irritants.

11. Pour obtenir de plus amples renseignements sur la sûreté,
voir le code “Code for safety in welding and cutting” CSA
Standard W 117.2-1974.

PRÉCAUTIONS DE SÛRETÉ POUR
LES MACHINES À SOUDER À
TRANSFORMATEUR ET À
REDRESSEUR

1. Relier à la terre le chassis du poste conformement au code
de l’électricité et aux recommendations du fabricant. Le dis­positif de montage ou la piece à souder doit être branché à
une bonne mise à la terre.

2. Autant que possible, I’installation et l’entretien du poste
seront effectués par un électricien qualifié.

3. Avant de faires des travaux à l’interieur de poste, la
debrancher à l’interrupteur à la boite de fusibles.

4. Garder tous les couvercles et dispositifs de sûreté à leur
place.

Mar. ‘93

v v

- MASTER TABLE OF CONTENTS FOR ALL SECTIONS -

MULTI-WELD 350

Page

Safety.................................................................................................................................................i-iv

Installation.............................................................................................................................Section A

Operation...............................................................................................................................Section B

Accessories ..........................................................................................................................Section C

Maintenance..........................................................................................................................Section D

Theory of Operation .............................................................................................................Section E

Troubleshooting and Repair................................................................................................Section F

Electrical Diagrams..............................................................................................................Section G

Parts Manual......................................................................................................................P361 Series

RETURN TO MAIN INDEX

Installation.............................................................................................................................Section A

Technical Specifications..............................................................................................................A-2

Safety Precautions......................................................................................................................A-3

Quick-Connect “Pig-Tails” ...........................................................................................................A-3

Attachment and Arrangement of “Pig-Tails”................................................................................A-3

Work Connection.........................................................................................................................A-4

Case Grounding..........................................................................................................................A-4

Inter-Connection of Converters...................................................................................................A-4

Power Source Setup...................................................................................................................A-6

Section A-1 Section A-1

TABLE OF CONTENTS

- INSTALLATION SECTION -

MULTI-WELD 350

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A-2 A-2

INSTALLATION

MULTI-WELD 350

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ELECTRICAL SPECIFICATIONS

Amps (DC+) Volts (DC+)

Output Rating @ 50°C (122°F) 350 34
Input Rating @ 50°C (122°F) 165 80
Max. Input Range 50-113 (Peak)
Max. O.C.V. 78
Output Preset Range 30-350 15-40

PHYSICAL DIMENSIONS

Height Width Depth Net Weight

11.6 in. 10.0 in. 21.5 in. 59.5 lbs.

295 mm 254 mm 546 mm 27.0 kg.

TEMPERATURE RANGES

Operating Temperature Range Storage Temperature Range

-40 to +122°F -40 to +185°F

-20 to +50°C -40 to +85°C

TECHNICAL SPECIFICATIONS - MULTI-WELD 350 (K1735-1)

Read this entire installation section before you
start installation.

SAFETY PRECAUTIONS

ELECTRIC SHOCK can kill.

• Do not touch electrically live
parts or electrodes with your
skin or wet clothing.

• Insulate yourself from the
work and ground.

• Always wear dry insulating
gloves.

Only qualified personnel should install, use, or ser­vice this equipment.

QUICK-CONNECT “PIG-TAILS”

The Multi-Weld 350 is factory provided with two 21
in.(53 cm) long 2/0 AWG (70 mm2) “pig-tail” cables.
Their 0.5" (13 mm) hole lug ends are routed through
the “INPUT +” (on back) and “ELECTRODE +” (on
front) cable channels of the Converter. They are
attached to the bottom-accessed covered cable con­nection studs.

Attach the preferred standard, user-provided Quick­connect terminal (such as Lincoln T wist-Mate or Tweco
2-MPC type) to the cut-off end of these cables. Use the
female connector on the “ELECTRODE +” cable and
the male connector on the “INPUT +” cable.

ATTACHMENT AND
ARRANGEMENT OF “PIG-TAILS”

To best suit the desired inter-connection of the
Converters, the “pig-tail” cables may be routed into the
front or back cable channels. For single or double “pig­tail” cables, route through the bottom-accessed cov­ered cable connection studs. (See Figures A.1
and B.1.)

To connect the “pig-tail” cables to the Converter:

1. Stand the Converter vertically on its rear handle
and skid to gain access to the bottom stud covers.
Then remove the two 0.25"(6.3 mm) screws secur­ing each cover and fold out the cover insulation.

2. Route the appropriate “pig-tail” cable lug ends
under the skid rail (for strain-relief) through the
desired front and/or rear corner channels to the
exposed 0.5" (13 mm) stud. Remove the flange
nut with a .75" (19 mm) wrench.

NOTE: Input supply cable(s) must connect through
“INPUT +” labeled channels, and output weld cable(s)
must connect through “ELECTRODE +” labeled
channels.

3. Slip the “pig-tail” cable lug(s) over the stud and re­secure the flange nut. Make sure that the lug(s) do
not touch any sheetmetal of the stud housing. Fold
back the cover insulation and replace the stud
cover.

A-3 A-3

INSTALLATION

MULTI-WELD 350

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WARNING

BOTTOM VIEW

TO ELECT.

TO ELECT.

TO

WORK

TO POWER

SOURCE

TO POWER

SOURCE

+

INPUT

+

ELECTRODE

ELECT.

+

ELECT.

+

+

IN

+

IN

FIGURE A.1 – PIG-TAIL CONNECTIONS

Be sure to follow the safety practice to
use the female connector on the cable
which would normally be electrically "hot"
(supply lead) if disconnected when the

system is energized, and the male on the
normally “cold” (load lead) side. If practical, shut off
power before connecting or disconnecting terminals.

WORK CONNECTION

Each Converter in the Multi-Weld system must have its
individual “Work” lead connected (clipped) to the work.
The #3 AWG (27 mm2) Work clip lead must have clean
metal connection to the work to complete the DC input
supply and output power circuits of the Multi-Weld 350.

Do not disconnect the Work clip lead without first
switching OFF the Converter panel switch. Failure to
do so will allow the Work lead clip to be electrically “hot”
to work and “hot” to the electrode, through the circuit of
the Converter, for about 5 seconds until the input con­tactor opens.

CASE GROUNDING

As shipped, the case of the Multi-Weld 350 is isolated
from all of the DC input and output welding terminals.
It is equipped with a grounding terminal screw
(.31” / 7.9 mm) marked with the symbol located on
the bottom rear of the base assembly . (Refer to the bot­tom view figure.) In order to comply with CSA and UL
case grounding specifications, this terminal is provided
for connection to weldment work that must be properly
grounded per methods meeting local and national elec­trical codes. Refer to “Safety in Welding, Cutting and
Allied Processes,” ANSI Z49.1 (US) and W117.2
(Canada).

Since any case fault would only involve the DC welding
circuit, the size of the grounding lead should have the
capacity to ground the potential fault current without
burning open. Use at least #6 AWG (13 mm

2

), but need
not exceed the size of the input cable supplying the
Multi-Weld 350.

Connect the Multi-Weld grounding lead to the work
piece separately from the Work clip. If the same clip is
used for both ground and work connection, the Multi­Weld case will be electrically “hot” to the work if the clip
is removed without first switching OFF the panel
switch. ( Refer to the Work clip WARNING).

INTER-CONNECTION OF
CONVERTERS

The input and electrode cables of the Multi-Weld 350
Converters may be inter-connected in a Multi-Weld
system using any combination of Distribution Box(es)
(see Figure B.1), paralleling (CC mode only) and
“daisy-chaining” (see Figure A.2). Choose the config­uration that best fits the field application setup within
the capacity of the power source supplying the system.

Power Source (Volts x Amp) capacity > 1.1 x

Sum of Converters’ (Volts x Amps) arcs

Paralelled units may be powered from more than one
source. Disconnect all inputs, including outputs from
other sources, before working on the equipment.
Before removing the parallel jumper, be sure both
Converters are switched OFF. If not, the male side of
the first disconnection will be electrically “hot” to work.

A-4 A-4

INSTALLATION

MULTI-WELD 350

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WARNING

WARNING

WARNING

A-5 A-5

INSTALLATION

MULTI-WELD 350

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DAISY CHAIN OPERATION

FIXED PARALLEL OPERATION

TO

WORK

TO POWER

SOURCE

TO WORK

TO ELECT.

TO POWER

SOURCE

TO WORK

TO ELECT.

TO WORK

TO ELECT.

SEPARABLE PARALLEL OPERATION

TO WORK

TO WORK

TO POWER

SOURCE

TO POWER

SOURCE

TO WORK

TO ELECT.

TO ELECT.

PARALLEL

JUMPER

+

IN

+

IN

ELECT.

+

+

IN

+

IN

ELECT.

+

+

IN

+

IN

ELECT.

+

+

IN

ELECT.

+

+

IN

+

IN

ELECT.

+

ELECT.

+

ELECT.

+

ELECT.

+

FIGURE A.2 – INTER-CONNECTING CONVERTERS

For Converters (operating at rated output) less than
200 ft. (61 m) from the power source, the following min­imum cable sizes are recommended for the indicated
quantity of Converters supplied by the input cable run
to keep cable temperature and voltage drop within
acceptable limits:

Converters Cable Size

on Cable AWG (mm2 )

1 1/0 (50)
2 2/0 (70)
3 3/0 (95)
4 4/0 (120)
5 2x3/0 (2x95)

The output “Electrode” cable should be 2/0 AWG
(70 mm

2

) if sized for rated output up to 200 ft.(61 m)
from the Converter. If paralleled, the output cable to the
arc should be 4/0 (120 mm

2

).

Do not disconnect the Work clip lead without first
switching OFF the Converter panel switch. Failure to
do so will allow the Work lead clip to be electrically “hot”
to work and “hot” to the electrode, through the circuit of
the Converter, for about 5 seconds until the input con­tactor opens.

POWER SOURCE SETUP

Refer to the Instruction Manual provided with the Multi­Source power source, or other DC power source being
used, for input power supply connections, output con­nections and controls setup.

In general:

1. Connect the positive (+) output connection terminal
to the input supplying the Multi-Weld system and
the negative (-) output connection terminal to the
work. (See Figure A.1.)

2. If not using a Multi-Source power source:
a. If an inductance control, or tap, is selectable,

use lowest inductance.

b. Use CC (Constant Current) mode for maximum

supply voltage.

c. Set panel output control to maximum for maxi-

mum current capacity.

d. Activate output with the “output terminals on”

switch, or jumper (2-4 on Lincoln Electric termi­nal strips).

A-6 A-6

INSTALLATION

MULTI-WELD 350

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WARNING

Operation...............................................................................................................................Section B

Safety Instructions.......................................................................................................................B-2

Product Description .....................................................................................................................B-3

Recommended Equipment and Processes.................................................................................B-4

Multi-System Power Source.................................................................................................B-4

Distribution Box.....................................................................................................................B-4

“Pig-Tail” Leads and Connectors ..........................................................................................B-4

Remote Output Control Options...........................................................................................B-5

CV Mode Wire Welding........................................................................................................B-5

CC Mode Stick Welding and Gouging..................................................................................B-5

Front Panel Controls...................................................................................................................B-6

Recessed Panel Controls............................................................................................................B-7

Paralleled Converters..................................................................................................................B-8

Remote Control of Paralleled Converters...................................................................................B-8

Transporting and Storage of the Multi-Weld 350........................................................................B-8

Cable Handling.....................................................................................................................B-8

Transporting..........................................................................................................................B-9

Storage.................................................................................................................................B-9

Protection Features .....................................................................................................................B-9

Fan as Needed (F.A.N.)........................................................................................................B-9

Over-Voltage Protection........................................................................................................B-9

Over-Current Protection........................................................................................................B-9

Over-Temperature Shutdown................................................................................................B-9

Section B-1 Section B-1

TABLE OF CONTENTS

- OPERATION SECTION -

MULTI-WELD 350

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OPERATING INSTRUCTIONS

Read and understand this entire section of operating
instructions before operating the machine.

SAFETY INSTRUCTIONS

ELECTRIC SHOCK can kill.

• Do not touch electrically live parts or
electrodes with your skin or wet clothing.

• Insulate yourself from the work and
ground.

• Always wear dry insulating gloves.

FUMES AND GASES CAN BE
DANGEROUS.

• Keep your head out of fumes.

• Use ventilation or exhaust to remove
fumes from breathing zone.

WELDING SPARKS CAN CAUSE
FIRE OR EXPLOSION.

• Keep flammable material away.

• Do not weld on containers that have held
combustibles.

ARC RAYS CAN BURN.

• Wear eye, ear, and body protection.

Observe additional Safety Guidelines detailed in
the beginning of this manual.

B-2 B-2

OPERATION

MULTI-WELD 350

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WARNING

PRODUCT DESCRIPTION

The Multi-Weld 350 Arc Converter (K1735-1) is part of
a Multi-Weld system, ideally suited for construction site
welding. It uses a single DC power source as the
only input supply and provides independent, full-range

control of up to 350A continuous with each Converter
arc for + polarity stick and wire processes, as well as
for arc-air gouging. (See Figure B.1.)

The Multi-Weld 350 is a DC to DC Converter that con­verts higher voltage/lower current input power to lower
voltage/higher current output power with over 90% effi­ciency.

For example, a single 600A continuous rated 70-80V
power source could supply up to five Multi-Weld 350
converters, each wire welding at 300 amps, or about
ten converters for stick welding at 150 amps with 26­29V at the arcs.

The Multi-Weld 350 Arc Converter is a single “world”
model built to IEC and CSA standards and meeting the
specific needs inherent to construction site welding:

Versatile

• Constant Current (CC) mode for stick and gouging.
Includes Hot Start and Arc Force controls to optimize
CC performance, and can be paralleled for higher
capacity welding and arc gouging.

• Constant Voltage (CV) mode for positive polarity
cored and solid wire welding with arc-powered feed­ers (such as the LN-25).

Portable

• The Multi-W eld 350 can be moved quickly. The light­weight Converter is easy to carry or pull and is small
enough to fit through a 15" (38 cm) diameter or 12" x
16" (31x 41 cm) elliptical man-hole.

• The Converter is powered by the welding cable from
the DC power source, without the safety hazard of
high AC input supply voltages.

• Welding controls are near the arc without long con­trol cables, and a receptacle is provided for an
optional remote for even closer user output control.

B-3 B-3

OPERATION

MULTI-WELD 350

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FIGURE B.1 – MULTI-WELD SYSTEM

Simple

• Easy installation with 10 ft. (3 m) work clip lead and
user preference quick-connect “pig-tails” for input
and electrode weld cables.

• Easy setup with only a few intuitive welding controls
and lit displays. This includes a single Power/Mode
switch with Input level light, and a single presettable
Output Control with separate digital meters for Amps
and Volts, featuring post-weld five second memory
display.

• Easy Service with quick-to-replace cable “pig-tails”
and “plug-in” assembly modules, including accessi­ble PC boards and interchangeable “plug-n-play”
panel instruments.

Robust

• Capacity is rated for continuous operation at 350
amps in 50°C (122°F) ambient temperature, and can
be paralleled to multiply CC mode output rating.

• Overload protection is provided with electronic limit­ing of output current, and with thermostat and over­voltage shutdown protection that automatically reset.

• Outdoor operation protected with sealed control and
power electronics compartments, with sealed inter­connections, housing “potted” circuit boards, and
using “Central-Air” cooling with “Fan-As-Needed” for
less dirt intake.

• Handling (and mishandling protection) is enhanced
with light, but durably designed, aluminum construc­tion with front to back, top and bottom, handles (also
serving as “roll bar” and skid), and a sheetmetal shell
attached with 1/4" steel threaded fasteners.

RECOMMENDED EQUIPMENT AND
PROCESSES

MULTI-SYSTEM POWER SOURCE

The Multi-Source 40KW, 80VDC buss power source
(K1752-1) is recommended for use in the Multi-Weld
system. However, other DC power sources capable of
supplying the required system buss current, at above
60 volts, may be used. It is recommended that this
power source have lower output inductance (choke)
such as the Lincoln Electric DC-1000, DC-655 or DC­600 set for maximum output in CC mode. The power
source output VA capacity should be 10% greater than
the sum of the maximum VA of the converter arcs,
which may all be simultaneously welding or gouging:

Power Source (Volts x Amps) capacity > 1.1 x

Sum of Converters’ (Volts x Amps) arcs

DISTRIBUTION BOX

The Multi-Weld Distribution Box (K1736-1) is available
for interconnection of the Multi-System using the same
“pig-tail” connection method provided with the Multi­Weld 350 converter. Six cable strain-relief ports are
provided for connection of up to (12) cables for distrib­ution or "daisy-chain" inter-connection to other boxes.
Four “pig-tail” leads (see below) are included with the
Box.

“PIG-TAIL” LEADS AND CONNECTORS

Accessory “pig-tail” leads and Twist-Mate connectors
are available from Lincoln for extra connections to the
Multi-Weld 350 or the Distribution Box:

Order No. Description:

CL012705 22 in.(56 cm) long 2/0 (70 mm

2

) cable
with 0.5 in.(13 mm) hole lug and cut-off
ends.

K852-70 Twist-Mate male insulated plug for

1/0-2/0 (50-70 mm

2

) cable.

K852-95 Twist-Mate male insulated plug for

2/0-3/0 (70-95 mm

2

) cable.

K1759-70 Twist-Mate female insulated receptacle

for 1/0-2/0 (50-70 mm

2

) cable.

K1759-95 Twist-Mate female insulated receptacle

for 2/0-3/0 (70-95 mm2) cable.

B-4 B-4

OPERATION

MULTI-WELD 350

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REMOTE OUTPUT CONTROL OPTIONS

The Multi-Weld 350 is provided with a 6-pin remote
receptacle to permit use with the 25 ft.(7.6 m) K857 or
100 ft. (30.4 m) K857-1 Remote Output Control
options. The remote receptacle can also be used with
the LN-25 equipped with the K444-1 Remote Control
option. These remotes have single-turn resolution on a
Minimum to Maximum numbered dialplate.

CV MODE WIRE WELDING

The Converter in CV mode was designed for use with
an arc-powered wire feeder like the LN-25. The
Converter output is always “hot” when the mode switch
is not OFF. Therefore it is recommended that the LN­25 model be equipped with the internal contactor in
order to have a “cold” electrode when the gun trigger is
released.

The CV mode recommended processes are positive
(+) polarity wire welding within the output capacity of
the Converter, including:

Flux Cored Arc Welding (FCAW)

Innershield: NS3M (5/64-3/32)

NR305 (.068)

Outershield: OS-70 (1/16-5/64)

OS-71 (.045-1/16)
MC-710 (.045-5/64)

Gas Metal Arc Welding (GMAW)

Carbon Steel: L50/56 (.030-1/16)

CC MODE STICK WELDING
AND GOUGING

The CC mode recommended processes are positive
(+) polarity stick and arc gouging within the output
capacity of single, or paralleled, Converters, including:

Shielded Metal Arc Welding (SMAW)

E6010/6011: FW5P/180 (3/32-1/4)

“fast-freeze”

E6013: FW37 (3/32-3/16)

“fill-freeze”

E7010/8010: SA85/70+ (3/32-7/32)

“fast-freeze” HT pipe

E7018/7028: JW LH70/3800 (3/32-5/32)

“low-hydrogen”

E7024/6027: JW1,3/2 (1/8-5/16)

“fast-fill”

Arc Air Carbon (AAC)

Gouging: Carbons (5/32-3/8)

B-5 B-5

OPERATION

MULTI-WELD 350

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FRONT PANEL CONTROLS

The numbered items of Figure B.2 match the num­bered items described below:

These few instruments and controls are basic to the
operation and monitoring of the Converter. They are
intuitively laid out so that the panel left side is weld cur­rent related, and the right side is weld voltage related:

(1) Input Power/ Mode Switch has three positions:

Center is OFF, which shuts off input power to the

Converter.

• Neither displays nor output is on if in OFF
position.

Left is on for CC (constant current) welding mode.

• Only AMPS digital meter is lit, displaying the
preset current setting.

• Output will be on at o.c.v. (open circuit voltage).

Right is on for CV (constant voltage) welding
mode.

• Only VOLTS digital meter is lit, displaying the
preset voltage setting.

• Output will be on at the output voltage setting.

(2) Output Control has 3-3/4 turn resolution with slip-

clutch to prevent control pot damage.
In CC mode it presets AMPS (30-350A range)

when not welding and adjusts actual arc current
while welding.

In CV mode it presets VOLTS (15-40v range)
when not welding and adjusts actual arc voltage
while welding.

(3) AMPS Digital Meter is a 3-1/2 digit LED meter

which displays:
Preset AMPS in CC mode when not welding.
“Blank” in CV mode when not welding.
Actual AMPS while welding in both CC and CV

modes.

B-6 B-6

OPERATION

MULTI-WELD 350

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FIGURE B.2 – FRONT PANEL CONTROLS

3

5

8

7

1

WORK

4

6

2

9

10

INPUT

+

ELECTRODE

+

Average AMPS for about 7 seconds after welding
stops in CC and CV modes only.

• The 5 second memory display is indicated by the
display’s left-most decimal point blinking, and is
interrupted if arc is restarted.

Accuracy of Actual AMPS is within 3%, and typical­ly within 10 amps of Preset.

• An Actual AMPS meter calibration adjustment
trimmer is provided. (See the Maintenance sec-
tion).

Two front screws secure the meter bezel, which
holds a replaceable spatter shield lens (Lincoln
part no. T14807-9).

(4) VOLTS Digital Meter is a 3-1/2 digit LED meter

which displays:
Preset VOLTS in CV mode when not welding.
“Blank” in CC mode when not welding.
Actual VOLTS while welding in both CV and CC

modes.
Average VOLTS for about 7 seconds after welding

stops in CV and CC modes only.

• The 7 second memory display is indicated by the
display’s left-most decimal point blinking, and is
interrupted if arc is restarted.

Accuracy of Actual VOLTS is within 3%, and typi­cally within 1 volt of Preset.

• An Actual VOLTS meter calibration adjustment
trimmer is provided. (See the Maintenance sec-
tion).

Two front screws secure the meter bezel, which
holds a replaceable spatter shield lens.

(5) Thermal Shutdown (yellow) Light turns on if out-

put is shutdown because internal overheating has
occurred. (See Over Temperature Shutdown in
this section).

(6) Input Voltage (green) Light indicates appropriate

level of input supply voltage:
“On” for adequate input voltage over 50 V for CC or

CV mode.
“Off” for inadequate input voltage under 50 V, no

input or Power Switch OFF.

NOTE: If green light is “blinking,” the input voltage may
be drifting above and below the 50 V level due to loads
on supply and cables. This may also cause the input
contactor to “chatter.”

RECESSED PANEL CONTROLS

These instruments are recessed behind a screw­secured hinged cover panel, and are not typically
required for normal operator access. They may be left
covered, as factory set, or set up as desired with or
without the hinged cover secured:

(7) Hot Start Control is provided to enhance arc

starting in both CC and CV modes with an extra
output “boost” at the arc strike that returns to the
setting level in less than a second (about 0.30
sec. in CC mode, and 0.045 sec. in CV mode).
This extra Hot Start amplitude is adjustable from
“0” (no extra) to “10” (100% of setting extra), with
the factory set “5” (center) position typically good
for most weld starting. However, “0” may provide
smoother starting for fine wire CV MIG.

(8) Arc Force Control is only functional in the CC

mode with Stick/Gouge slope. (See below). Arc
Force prevents “stubbing” of the electrode by pro­viding extra weld current if the arc voltage drops
below about 14 V. This extra weld current is
adjustable from “-10” (no extra) to “+10” (60% of
setting extra), with the factory set “0” (center)
position typically good for most welding.

(9) CC Slope Switch is provided to enhance stick

welding on “fast-freeze” type electrodes (such as
E6010 and E7010) typically used on pipe welding
applications for fast root pass vertical down
"drag" technique (not “whipping”). For this type of
application, improved operating appeal may be
obtained if the CC Slope is switched from the fac­tory set STICK/GOUGE position to the PIPE
position.

NOTE: The PIPE position uses a “drooping” type
slope (~22v/100A), so preset current (not actual
current) accuracy may be affected if arc length
voltage is not maintained at the typical 28 V used
for these electrodes. Typically this error should
not be more than about 10 A.

(10) Remote Control Receptacle is provided to per-

mit the use of an optional Remote output control
to provide operator control even closer to the arc.

Connecting the Remote plug to this receptacle
automatically transfers output control from the
panel Output Control (item (2) above) to the
Remote pot control, which will function the same
but with only single-turn resolution.

B-7 B-7

OPERATION

MULTI-WELD 350

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Disconnecting the Remote plug from this recepta­cle automatically transfers output control back to
the panel Output Control (item (2) above).

Remote output On/Off switching can also be done
through this Remote Control receptacle by per­forming the following wiring changes:

1. Making sure the input to the Converter is

removed, remove the case wraparound.

2. Locate the 4-pin plug (P21) on the back panel

of the control box module, and cut the jumper
lead looping from the back of the plug. (Refer to
the Wiring Diagram in the Electrical Diagrams
section.) Insulate the cut lead ends and leave
long enough to possibly splice back together
again at some future time.

3. Replace the case wraparound.

4. Connect a user-provided remote switch be-

tween pins D and E of an MS3106A-18-12P
plug (Lincoln part no. S12020-27 with S12024­1 cable clamp). See the diagram below:

Pin: Remote Function:

A Max. of 10K pot
B Wiper of 10K pot
C Min. of 10K pot
D Output Switch
E Output Switch
F No connection

5. Connect this switch plug to the Multi-Weld 350

Remote Control Receptacle (10) with switch
opened. Closing the switch activates the
Converter output.

PARALLELED CONVERTERS

Multi-Weld 350 converters that are paralleled (see INTER­CONNECTION OF CONVERTERS in the Installation
section) must each be set up in the same manner in order
to manage the arc current drawn from each:

1. Set to CC mode with CC SLOPE switch set to
STICK/GOUGE.

2. Preset Output Controls of both paralleled
Converters to ~1/2 desired total AMPS.

If arc current from each Converter gets too out of bal­ance (primarily a problem if trying to use CV mode) the
hotter running Converter could go into current-limiting
and/or Thermal shutdown (See OVER-TEMPERA­TURE SHUTDOWN in the Installation section.) This
might then overload the other, or at least interrupt the
operator’s process. However, no damage will occur to
the Converters.

REMOTE CONTROL OF
PARALLELED CONVERTERS

(FOR CC STICK/GOUGE MODE ONLY)

Full Range remote control can be accomplished with a
separate optional Remote output control (see the
Installation section) connected to each Converter. The
current contribution of each Converter will depend on
its remote output setting.

Partial Range remote control can be accomplished with
a single Remote Control connected to the output
Converter. The input Converter must be preset with its
panel Output Control to below the minimum desired
output range. The Remote Control, connected to the
output Converter, will control its output to add to the
preset level.

Remote Output On/Off switching may be set up for
each of the paralleled Converters. Electrically isolated
switches must be used to activate each separately but
simultaneously.

TRANSPORTING AND STORAGE
OF THE MULTI-WELD 350

CABLE HANDLING

The input and electrode cables are easily disconnect­ed from the quick-connect “pig-tails.” The Work lead
can be reeled around the Multi-Weld 350 case cradled
by the base skid handles, to which the clip can be
secured.

B-8 B-8

OPERATION

MULTI-WELD 350

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F

A

B

E
D

C

TRANSPORTING

The Converter may be carried by one or two persons
using the front and rear top and bottom handles. It can
also be set vertically on a two wheel cart, or horizon­tally on a wagon, to move it longer distances.

STORAGE

The Multi-Weld 350 may be set on a floor , or shelf, hor­izontally on its skid, or vertically standing on its rear top
and bottom handles.

PROTECTION FEATURES

The Multi-Weld 350 design features electronic protec­tion systems to help assure reliable operation even
under adverse conditions. These systems include:

FAN AS NEEDED (F.A.N.)

The cooling fan will turn on when the arc starts and
remain on for about a minute after the arc is out to cool
down the power components.

This feature electronically controls the fan so it does
not run continuously when the power switch is turned
on. This will minimize the amount of contaminate and
clogging debris which may be drawn into the
Converter. It enhances the “Central-Air” system design
which intakes lower velocity air through the higher side
louvers and blows it out through the lower back louvers
with higher velocity.

OVER-VOLTAGE PROTECTION

The Multi-Weld 350 input contactor will open if the input
supply voltage is above 1 13 VDC, and will automatical­ly reclose if the voltage drops back below. During Over­Voltage Shutdown the panel displays will be as appro­priate for the non-welding mode. (See FRONT PANEL
CONTROLS in this section.)

When the contactor recloses, the output of the
Converter will reactivate. Switching OFF input power
prevents unexpected reactivation.

This feature protects internal components of the
Converter from excessive voltage levels.

OVER-CURRENT PROTECTION

The maximum output current of the Multi-Weld 350 is
electronically limited, to protect internal power compo­nents, so as not to exceed about 375 amps average
and 500 amps peak. When the current load starts to
exceed these limits, the output is reduced (lower volt­age) to sustain these maximum levels until the current
is reduced, even to a shorted output.

Prolonged output at this maximum current limit level
may eventually overheat the Converter’s internal
power components, causing over-temperature shut­down. (See following section.)

Short circuit protection is also provided to reduce max­imum output current to about 200 amps, if the output
voltage is reduced, by loading or current limiting, to
below 14 volts for over 7 seconds (indicating a shorted
output). The output current must be interrupted to reset
this reduced protective level.

This maximum 200 amp short circuit level will allow
using the Multi-Weld 350 for “pipe-thawing” applica­tions without causing over-temperature shutdown.
(See following section.)

OVER-TEMPERATURE SHUTDOWN

A second over-load protection switch in the Imbalance
Protector Module was added to Multi-Weld 350 models
with codes 10736 and higher. This module senses for
an imbalance of current between the paralleled
Chopper boards by sensing the differential choke volt­age. If this voltage exceeds 1 V for a sustained time,
the Imbalance Protector will also activate over-temper­ature shutdown to protect the higher current Chopper
board from over heating.

When the thermostat resets, the output of the
Converter will reactivate. Switching OFF input power
prevents reactivation but also shuts off the cooling fan,
which prolongs the reset time.

During Over-Temperature Shutdown the panel displays
will be as appropriate for the non-welding mode. (See
FRONT PANEL CONTROLS in this section.) The fan
will remain running and the Thermal Shutdown (yellow)
Light will be lit until reset. Typically, if shutdown occurs
repeatedly below 300 amps output with fan running,
imbalance of the Chopper board current may likely be
the cause.

B-9 B-9

OPERATION

MULTI-WELD 350

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CAUTION

CAUTION

B-10 B-10

NOTES

MULTI-WELD 350

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Accessories ..........................................................................................................................Section C

Options/Accessories ...................................................................................................................C-2

Field Installed Options ....................................................................................................... ..C-2

Semiautomatic Welding Accessories..........................................................................................C-2

Connection of Lincoln Electric Wire Feeders..............................................................................C-2

Connection of the LN-25 ......................................................................................................C-3

Section C-1 Section C-1

TABLE OF CONTENTS

- ACCESSORIES SECTION -

MULTI-WELD 350

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OPTIONS/ACCESSORIES

The following options/accessories are available for
your Multi-Weld 350 from your local Lincoln Distributor.

FIELD INSTALLED OPTIONS

K1736-1 DISTRIBUTION BOX - Makes connecting up

to 10 Multi-Weld 350s quick and easy. Contains cop­per bus bar for connecting multiple “pig-tails.” Four
“pig-tails” included.

K857 25 ft. (7.5 m) or K857-1 100 ft. (30.4 m)
REMOTE CONTROL - Provides 25 ft. or 100 ft. (7.5 m

or 30 m) of remote output control. Connects to 6-pin
receptacle on front of Multi-Weld 350.

WELDING CABLE CONNECTORS

Twist-Mate™ plug for fast connection of additional
Multi-Weld 350s.

K852-70 - Twist-Mate male plug for 1/0-2/0 (500­70 mm

2

) cable.

K852-90 - Twist-Mate male plug for 2/0-3/0 (70­95 mm

2

) cable.

K1759-70 - Twist-Mate female plug for 1/0-2/0 (50­70 mm2) cable.

K1759-90 - Twist-Mate female plug for 2/0-3/0 (70­95 mm

2

) cable.

SEMIAUTOMATIC WELDING
ACCESSORIES

K449 LN-25 WIRE FEEDER - The LN-25 is perfect for

use with the Multi-Weld 350. It is designed to run
“across-the-arc” with no control cables. This portable
wire feeder offers constant wire feed speed in a rugged
case.

CONNECTION OF LINCOLN
ELECTRIC WIRE FEEDERS

ELECTRIC SHOCK can kill.

• Only qualified personnel should per­form this maintenance.

• Turn the input power OFF at the dis­connect switch or fuse box before
working on this equipment.

• Do not touch electrically hot parts.

C-2 C-2

ACCESSORIES

MULTI-WELD 350

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WARNING

CONNECTION OF THE LN-25 TO THE
MULTI-WELD 350 “ACROSS THE ARC”
(SEE FIGURE C.1.)

1. Shut the welder off.

2. Connect the electrode cable from the LN-25 to the
“+” terminal of the welder.

NOTE: Welding cable must be sized for current and
duty cycle of application.

3. Attach the single lead from the LN-25 to the work
using the spring clip on the end of the lead. This is
only a sense lead – it carries no welding current.

If you are using an LN-25 without an internal contactor,
the electrode will be “HOT” when the Multi-Weld 350 is
turned ON.

4. Set the MODE switch to “CV.”

5. Adjust wire feed speed at the LN-25.

6. Adjust the HOT START CONTROL to the desired
level. (Use “O” for fine wire.)

7. Set VOLTMETER switch to the positive position.

C-3 C-3

ACCESSORIES

MULTI-WELD 350

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AMPHENOL

TO WORK

WORK CLIP LEAD

LN-25

WIRE FEEDER

OPTIONAL K444

REMOTE CONTROL

TO WORK

ELECTRODE

6 PIN

TO WORK

CAUTION

FIGURE C.1

MULTI-WELD 350/LN-25 ACROSS THE ARC CONNECTION DIAGRAM

C-4 C-4

NOTES

MULTI-WELD 350

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Maintenance..........................................................................................................................Section D

Safety Precautions ......................................................................................................................D-2

Maintenance................................................................................................................................D-2

Digital Meter Calibration..............................................................................................................D-2

Service........................................................................................................................................D-3

Section D-1 Section D-1

TABLE OF CONTENTS

- MAINTENANCE SECTION -

MULTI-WELD 350

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SAFETY PRECAUTIONS

ELECTRIC SHOCK can kill.

• Do not touch electrically live parts or
electrode with skin or wet clothing.

• Insulate yourself from work and ground.

• Always wear dry insulating gloves.

Have qualified personnel do the maintenance work.
Always use the greatest care when working near mov-

ing parts.
If a problem cannot be corrected by following the

instructions, take the machine to the nearest Lincoln
Field Service Shop.

See additional warning information throughout this
manual.

MAINTENANCE

The only maintenance that may be required for the
Multi-Weld 350 is to clean out any accumulated dirt and
debris. Clogging could contaminate internal compo­nents or obstruct proper cooling of the power compo­nents, resulting in premature over-temperature shut­down.

The recommended cleaning procedure is as follows:

1. Be sure to disconnect the Converter input cable to
remove its input power.

2. Remove the four screws securing the rear louver
panel and remove the panel to expose the cooling
tunnel heatsinks. (See Figure D.1 below.)

3. Holding the unit by the front handles, so the back is
facing down, shake the loose debris out of the unit.
Raking out the heatsink fins may be necessary for
jammed debris.

4. If necessary, remove the case wraparound cover.
Using the skid handles to hold the unit upside down,
carefully dump out any remaining loose debris or
carefully blow out using low pressure air.

5. Reassemble the cleaned out Converter by reversing
the above steps.

DIGITAL METER CALIBRATION

If calibration of either digital meter is ever necessary,
meter calibration adjustment trimmers are provided on
the Weld Control PC board inside the Control Module.
(See Figure D.2.) Calibration must be done with an
Output current load, so meters are displaying Actual
(not Preset) values. It is recommended that the cali­bration levels be near the rating plate values, for best
accuracy, and compared to "master" meters with better
than 2% accuracy.

The accuracy of Actual AMPS meter should be within
3% of the welding amps monitored. The AMPS meter
trimmer (R561) is located near the center of the Weld
Control PC board just below the VOLTS meter trimmer
(R562). Clockwise rotation of the trimmer adjustment
screw will decrease the meter reading.

The accuracy of Actual VOLTS meter should be within
3% of the welding volts monitored. The VOLTS meter
trimmer (R562) is located near the center of the Weld
Control PC board just above the AMPS meter trimmer
(R561). Clockwise rotation of the trimmer adjustment
screw will decrease the meter reading. The “master”
voltmeter should be connected as close as possible to
the “ELECTRODE +” stud and “WORK -” lead bolt for
best accuracy.

D-2 D-2

MAINTENANCE

MULTI-WELD 350

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WARNING

FIGURE D.1 – TUNNEL HEATSINKS

SERVICE

The Multi-Weld 350 was designed for easy service
using quick-to-replace components and assembly
modules that can be simply swapped out at the job site
to minimize down time. More prolonged troubleshoot­ing and repair of the module may be done later on the
service bench.

Figure D.2 shows the three assembly modules of the
Converter which are covered with the Case
Wraparound (item (4):

Control Module (item (1) is removed from the Base
Module assembly by removing the two bottom
accessed screws and disconnecting the three sealed
harness plugs from the receptacles on the back of the
Control box.

This module is a sealed enclosure containing replace­able electronic components:

• Sealed back cover which mounts the internal “pot-
ted” Weld Control and Peripheral PCBs.

• Front panel with “plug-n-play” instruments that indi-
vidually plug to the Control PCB.

• Interchangeable “potted” digital meters with front
replaceable spatter shield lenses.

• Harness lead receptacles that connect to Base
Module harness lead plugs.

Tunnel Module (item (2) is removed from the Base
Module assembly by removing the four bottom
accessed screws and disconnecting the two sealed
harness plugs and power leads.

NOTE: Removal of Control Module improves access to
disconnect Tunnel Module power leads.

This module assembly includes:

• Heatsinked power switching (IGBT) boards and iso­lated diodes.

• Capacitors and potted power supply boards.

• Fan and sheetmetal bulkhead tunnel and component

enclosure.

• Harness lead receptacles and power leads that con-

nect to Base Module.
Base Module (item (3) is the mounting and connection

platform for the other modules.
This module assembly includes:

• Base sheetmetal with input/output connection cham­bers with "pigtail" leads.

• Input contactor, input diodes heat sink assembly and
Work clip lead.

• Output chokes and current shunt.

• Lead harness sealed plugs connect to Tunnel and

Control Module receptacles.

D-3 D-3

MAINTENANCE

MULTI-WELD 350

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2

4

1

3

FIGURE D.2 – MAJOR COMPONENT LOCATIONS

1. CONTROL MODULE

2. TUNNEL MODULE

3. BASE MODULE

4. CASE WRAPAROUND

D-4 D-4

NOTES

MULTI-WELD 350

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General Description .......................................................................................................................E-2

Input Power Source, Contactor and DC Buss Power Supply Board..........................................E-2

Power Modules and Feedback ...................................................................................................E-3

Analog Control Power Supply Board and Weld Control Board .................................................E-4

Mode Selector and Output Controls............................................................................................E-5

Protection Features .....................................................................................................................E-6

Insulated Gate Bipolar Transistor (IGBT) Operation...................................................................E-7

Pulse Width Modulation ..............................................................................................................E-8

Chopper Technology Fundamentals ...........................................................................................E-9

Section E-1 Section E-1

TABLE OF CONTENTS

- THEORY OF OPERATION SECTION -

MULTI-WELD 350

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CHOKE

IGBT

IGBT

SHUNT

WORK

TO ELECTRODE

CABLE

+

ANALOG

CONTROL

POWER

SUPPLY

BOARD

WELD

CONTROL

BOARD

ARC
FORCE
CONTROL

OUTPUT

CONTROL

HOT
START

DC

BUS
POWER
SUPPLY

BOARD

FAN

+

DC

POWER

SOURCE

(EXTERNAL)

_

REMOTE

RECEPTACLE

INPUT
DIODES

INPUT

CONTACTOR

MULTI-WELD 350 BLOCK LOGIC DIAGRAM

CC SLOPE

(STICK/GOUGE or PIPE)

PERIPHERAL

BOARD

INPUT
INDICATOR
LIGHT

ON/OFF
MODE
SWITCH
(1/2)

CR1

CHOPPER MODULE

CHOPPER MODULE

ON/OFF
MODE
SWITCH
(1/2)

VOLTS

AMPS

THERMAL
LIGHT

FREEWHEELING DIODE

FREEWHEELING DIODE

REGULATED
VOLTAGES

CR1
COIL

15 VDC

CURRENT FEEDBACK
TO WELD CONTROL BOARD

20
VDC
x 2

-

INPUT

CAPACITORS

40
VDC

LEFT AND RIGHT
CHOPPER MODULES

GATE
SIGNALS

40 VDC

FIGURE E.1 – MULTI-WELD 350 BLOCK LOGIC DIAGRAM

GENERAL DESCRIPTION

The MULTI-WELD 350 Converter uses a single DC
input power source to provide up to 350 continuous
amps for positive polarity stick, wire processes, and
arc-air gouging. The machine converts higher volt­age/lower current DC input power to lower
voltage/higher current DC output power with over 90%
efficiency. This DC output is controlled by Chopper
Technology to produce DC current for multi-purpose
welding applications.

INPUT POWER SOURCE,
CONTACTOR AND DC BUSS
POWER SUPPLY BOARD

The Multi-Weld 350 receives DC input power from an
80 VDC buss Multi-Source (recommended), although
other external DC sources such as the Lincoln Electric
DC-1000, DC-655, or DC-600 can be used if they pro­duce 50 VDC or above.

The +50 VDC supply voltage is applied to the input
contactor via two large input diodes. The input contac­tor establishes the electrical connection between the
Multi-Weld 350 and the power source when the
ON/OFF MODE switch is activated in either the con­stant current (CC-stick) mode or the constant voltage
(CV-wire) mode.

A 40 VDC Buss Power Supply Board supplies 40 VDC
power to the Analog Control Power Supply Board,
which in turn feeds regulated voltages to a Weld
Control Board and 15 VDC to the Peripheral Board.
The Peripheral Board powers the input contactor coil
and the input indicator light on the front panel. The 40
VDC is also supplied to the Peripheral Board and is
passed on to the Weld Control Board.

E-2 E-2

THEORY OF OPERATION

MULTI-WELD 350

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FIGURE E.2 – INPUT POWER SOURCE, CONTACTOR AND DC BUSS POWER SUPPLY BOARD

NOTE: Unshaded areas of Block Logic Diagram are the subject of discussion.

MULTI-WELD 350 BLOCK LOGIC DIAGRAM

+

DC

POWER

SOURCE

(EXTERNAL)

_

INPUT
DIODES

ON/OFF
MODE
SWITCH
(1/2)

CONTACTOR

DC

BUS

POWER

SUPPLY

BOARD

INPUT

CR1

INPUT

CAPACITORS

40
VDC

LEFT AND RIGHT
CHOPPER MODULES

CHOPPER MODULE

CHOPPER MODULE

20
VDC
x 2

ANALOG

CONTROL

POWER

SUPPLY

BOARD

15 VDC

PERIPHERAL

BOARD

IGBT

IGBT

GATE
SIGNALS

REGULATED
VOLTAGES

FAN

40 VDC

FREEWHEELING DIODE

FREEWHEELING DIODE

ON/OFF
MODE
SWITCH
(1/2)

CONTROL

ARC
FORCE
CONTROL

CR1
COIL

INPUT
INDICATOR
LIGHT

CHOKE

VOLTS

WELD

BOARD

OUTPUT

CONTROL

HOT
START

AMPS

THERMAL
LIGHT

SHUNT

CURRENT FEEDBACK
TO WELD CONTROL BOARD

REMOTE

RECEPTACLE

CC SLOPE

(STICK/GOUGE or PIPE)

TO ELECTRODE

CABLE

+

WORK

-

POWER MODULES AND FEED­BACK

The external DC source voltage is applied to parallel
capacitors incorporated within each of the two Power
(Chopper) Modules. These capacitors function as fil­ters and as power supplies for the IGBTs. See IGBT
Operation in this section. The IGBTs act as high­speed switches operating at 20KHZ. These devices
are switched on and off by the Weld Control Board
through pulse width modulation gate signals. See
Pulse Width Modulation in this section. This
“chopped” DC output is applied through choke coils
and a shunt to the welding output terminals. The

chokes function as current filters. Free-wheeling
diodes are incorporated in the power circuit to provide
a current path for the stored energy in the chokes when
the IGBTs are turned off. See Chopper Technology in
this section.

Output voltage and current feedback information is fed
to the Weld Control Board. This information is sensed
from the output terminal circuits and the shunt. The
feedback information is processed by the Weld Control
Board, which regulates output voltage and current.

E-3 E-3

THEORY OF OPERATION

MULTI-WELD 350

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NOTE: Unshaded areas of Block Logic Diagram are the subject of discussion.

FIGURE E.3 – POWER MODULES AND FEEDBACK

MULTI-WELD 350 BLOCK LOGIC DIAGRAM

+

DC

POWER

SOURCE

(EXTERNAL)

_

INPUT
DIODES

ON/OFF
MODE
SWITCH
(1/2)

CONTACTOR

DC

BUS

POWER

SUPPLY

BOARD

INPUT

CR1

INPUT

CAPACITORS

40
VDC

LEFT AND RIGHT
CHOPPER MODULES

CHOPPER MODULE

CHOPPER MODULE

20
VDC
x 2

ANALOG

CONTROL

POWER

SUPPLY

BOARD

15 VDC

PERIPHERAL

BOARD

IGBT

IGBT

GATE
SIGNALS

REGULATED
VOLTAGES

FAN

40 VDC

FREEWHEELING DIODE

FREEWHEELING DIODE

ON/OFF
MODE
SWITCH
(1/2)

CONTROL

ARC
FORCE
CONTROL

CR1
COIL

INPUT
INDICATOR
LIGHT

CHOKE

VOLTS

WELD

BOARD

OUTPUT

CONTROL

HOT
START

AMPS

THERMAL
LIGHT

SHUNT

CURRENT FEEDBACK
TO WELD CONTROL BOARD

REMOTE

RECEPTACLE

CC SLOPE

(STICK/GOUGE or PIPE)

TO ELECTRODE

CABLE

+

WORK

-

ANALOG CONTROL POWER
SUPPLY BOARD AND WELD
CONTROL BOARD

The Analog Control Power Supply Board, which is pow­ered by 40 VDC delivered from the DC Buss Power
Supply Board, supplies various regulated DC voltages
to operate the Weld Control Board circuitry. It also pro­vides two regulated 20 VDC supplies to operate the
electronics on the Chopper Module Boards and applies
a 15 VDC supply to the Peripheral Board.

The Weld Control Board monitors the operator controls
(arc control, output control, hot start control, mode
selector switch, CC Slope switch and the remote con­trol receptacle). It compares these commands to the

current and voltage feedback information it receives
from the shunt and output terminal circuits. The cir­cuitry on the Weld Control Board determines how the
output should be controlled to optimize welding results,
and it sends the correct PWM gate signals to the IGBT
driver circuits. The Weld Control Board commands the
voltmeter and ammeter, which display both preset and
actual (while welding) voltage and current. The Weld
Control Board also controls the cooling fan motor and
the thermal indicator (light).

E-4 E-4

THEORY OF OPERATION

MULTI-WELD 350

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NOTE: Unshaded areas of Block Logic Diagram are the subject of discussion.

FIGURE E-4 – ANALOG CONTROL POWER SUPPLY BOARD AND WELD CONTROL BOARD

MULTI-WELD 350 BLOCK LOGIC DIAGRAM

+

DC

POWER

SOURCE

(EXTERNAL)

_

INPUT
DIODES

ON/OFF
MODE
SWITCH
(1/2)

CONTACTOR

DC

BUS
POWER
SUPPLY

BOARD

INPUT

CR1

INPUT

CAPACITORS

40
VDC

LEFT AND RIGHT
CHOPPER MODULES

CHOPPER MODULE

CHOPPER MODULE

20
VDC
x 2

ANALOG

CONTROL

POWER

SUPPLY

BOARD

15 VDC

PERIPHERAL

BOARD

IGBT

IGBT

GATE
SIGNALS

REGULATED
VOLTAGES

FAN

40 VDC

FREEWHEELING DIODE

FREEWHEELING DIODE

ON/OFF
MODE
SWITCH
(1/2)

CONTROL

ARC
FORCE
CONTROL

CR1
COIL

INPUT
INDICATOR
LIGHT

CHOKE

VOLTS

WELD

BOARD

OUTPUT

CONTROL

HOT
START

AMPS

THERMAL
LIGHT

SHUNT

CURRENT FEEDBACK
TO WELD CONTROL BOARD

REMOTE

RECEPTACLE

CC SLOPE

(STICK/GOUGE or PIPE)

TO ELECTRODE

CABLE

+

WORK

-

MODE SELECTOR AND OUTPUT
CONTROLS

In CC mode, machine output is at open circuit voltage.
The OUTPUT control presets amps in the 30 to 350 A
range and then adjusts actual welding current to match
the preset when welding. In CV mode, machine output
is at the voltage level set at the OUTPUT control. The
OUTPUT control presets volts, then adjusts the actual
arc voltage to match the preset when welding.

A HOT START control is provided to enhance arc start­ing with an adjustable output “boost” in either CC or CV
mode. The ARC FORCE control (CC mode only) pro­vides extra weld current to prevent electrode “stubbing”
An additional CC SLOPE switch improves “fast-freeze”
stick electrode performance during vertical pipe weld­ing when set to the PIPE position.

E-5 E-5

THEORY OF OPERATION

MULTI-WELD 350

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NOTE: Unshaded areas of Block Logic Diagram are the subject of discussion.

FIGURE E.5 – MODE SELECTOR AND OUTPUT CONTROLS

MULTI-WELD 350 BLOCK LOGIC DIAGRAM

+

DC

POWER

SOURCE

(EXTERNAL)

_

INPUT
DIODES

ON/OFF
MODE
SWITCH
(1/2)

CONTACTOR

DC

BUS

POWER

SUPPLY

BOARD

INPUT

CR1

INPUT

CAPACITORS

40
VDC

LEFT AND RIGHT
CHOPPER MODULES

CHOPPER MODULE

CHOPPER MODULE

20
VDC
x 2

ANALOG

CONTROL

POWER

SUPPLY

BOARD

15 VDC

PERIPHERAL

BOARD

IGBT

IGBT

GATE
SIGNALS

REGULATED
VOLTAGES

FAN

40 VDC

FREEWHEELING DIODE

FREEWHEELING DIODE

ON/OFF
MODE
SWITCH
(1/2)

CONTROL

ARC
FORCE
CONTROL

CR1
COIL

INPUT
INDICATOR
LIGHT

CHOKE

VOLTS

WELD

BOARD

OUTPUT

CONTROL

HOT
START

AMPS

THERMAL
LIGHT

SHUNT

CURRENT FEEDBACK
TO WELD CONTROL BOARD

REMOTE

RECEPTACLE

CC SLOPE

(STICK/GOUGE or PIPE)

TO ELECTRODE

CABLE

+

WORK

-

PROTECTION FEATURES

The Multi-Weld 350 design features electronic protec­tion systems to help assure reliable operation even
under adverse conditions. These systems include:

FAN AS NEEDED (F.A.N.)

The cooling fan will turn on when the arc starts and
remain on for about a minute after the arc is out to cool
down the power components.

This feature electronically controls the fan so it does
not run continuously when the power switch is turned
on. This will minimize the amount of contaminate and
clogging debris that may be drawn into the converter.
The “Central-Air” system design intakes lower velocity
air through the higher side louvers and blows it out
through the lower back louvers with higher velocity.

OVER-TEMPERATURE SHUTDOWN

The Multi-Weld 350 has a temperature sensing ther­mostat on the input diode heat sink to protect the
power components within the converter from overheat­ing. If this thermostat temperature exceeds about 95
degrees C (203 degrees F), the converter will electron­ically shut off the output and turn on the Thermal
Shutdown (yellow) Light until the thermostat is cooled
enough to reset.

When the thermostat resets, the converter output will
reactivate. Switching OFF input power prevents reac­tivation but also shuts off the cooling fan, which pro­longs the reset time.

During over-temperature shutdown the panel displays
will be appropriate for the non-welding mode.
However, the fan will remain running and the Thermal
Shutdown Light will be lit until reset.

OVER-CURRENT PROTECTION

The maximum output current of the Multi-Weld 350 is
electronically limited so as not to exceed 375 amps
average and 500 amps peak to protect internal power
components. When the current load starts to exceed
these limits, the output is reduced (lower voltage) to
sustain maximum levels until the current is reduced,
even to a shorted output.

Prolonged output at this maximum current limit level
may eventually over heat the converter’s internal
power components, causing over-temperature shut­down.

Short circuit protection is also provided to reduce max­imum output current to about 200 amps if the output
voltage is reduced, by loading or current limiting, to
below 14 volts for over 7 seconds (indicating a shorted
output). The output current must be interrupted to
reset this reduced protective level.

This maximum 200 amp short circuit level will allow
using the Multi-Weld 350 for “pipe-thawing” applica­tions without causing over-temperature shutdown.

When the contactor recloses, the converter output will
reactivate. Switching OFF input power prevents unex­pected reactivation.

This feature protects internal components of the con­verter from excessive voltage levels.

OVER-VOLTAGE PROTECTION

The Multi-Weld 350 input contactor will open if the input
supply voltage is above 113 VDC, and it will automati­cally reclose if the voltage drops back to 113 VDC.
During over-voltage shutdown the panel displays will
be as appropriate for the non-welding mode.

E-6 E-6

THEORY OF OPERATION

MULTI-WELD 350

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CAUTION

CAUTION

INSULATED GATE BIPOLAR
TRANSISTOR (IGBT) OPERATION

An IGBT is a type of transistor. IGBTs are semicon­ductors well suited for high frequency switching and
high current applications.

Drawing Ashows an IGBT in a passive mode. There is
no gate signal, zero volts relative to the source, and
therefore, no current flow. The drain terminal of the
IGBT may be connected to a voltage supply; but since
there is no conduction the circuit will not supply current
to components connected to the source. The circuit is
turned off like a light switch in the OFF position.

Drawing B shows the IGBT in an active mode. When
the gate signal, a positive DC voltage relative to the
source, is applied to the gate terminal of the IGBT, it is
capable of conducting current. A voltage supply con­nected to the drain terminal will allow the IGBT to con­duct and supply current to circuit components coupled
to the source. Current will flow through the conducting
IGBT to downstream components as long as the posi­tive gate signal is present. This is similar to turning ON
a light switch.

E-7 E-7

THEORY OF OPERATION

MULTI-WELD 350

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FIGURE E.6 – IGBT OPERATION

DRAIN

SOURCE

GATE

INJECTING LAYER

BUFFER LAYER

DRAIN DRIFT REGION

BODY REGION

p +

n +

n -

p

n + n +

DRAIN

SOURCE

GATE

INJECTING LAYER

BUFFER LAYER

DRAIN DRIFT REGION

BODY REGION

p +

n +

n -

p

n + n +

POSITIVE
VOLTAGE
APPLIED

B. ACTIVE

A. PASSIVE

PULSE WIDTH MODULA TION

The term PULSE WIDTH MODULATION is used to
describe how much time is devoted to conduction in the
cycle. Changing the pulse width is known as MODU­LA TION. Pulse Width Modulation (PWM) is the varying
of the pulse width over the allowed range of a cycle to
affect the output of the machine.

MINIMUM OUTPUT

By controlling the duration of the gate signal, the IGBT
is turned on and off for different durations during a
cycle. The top drawing shows the minimum output sig­nal possible over a 50-microsecond time period.

The positive portion of the signal represents one IGBT
group conducting for 2 microsecond. The dwell time (off
time) is 48 microseconds. Since only 2 microseconds of
the 50-microsecond time period is devoted to conduct­ing, the output power is minimized.

MAXIMUM OUTPUT

By holding the gate signals on for 48 microseconds and
allowing only 2 microseconds of dwell time (off time)
during the 50-microsecond cycle, the output is maxi­mized. The darkened area under the top curve can be
compared to the area under the bottom curve. The
more darkened area under the curve, the more power
is present.

E-8 E-8

THEORY OF OPERATION

MULTI-WELD 350

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FIGURE E.7 – TYPICAL IGBT OUTPUTS



MINIMUM OUTPUT

(Dwell or Off Time)

sec

2

MAXIMUM OUTPUT

48

50

sec

sec

(Dwell or Off Time)

sec

48

sec

50

CHOPPER TECHNOLOGY
FUNDAMENTALS

The new era of welding machines such as the Multi­Weld 350 employ a technology whereby a DC source
is turned on and off (chopped up) at high speed, then
smoothed through an inductor to control an arc.

Hence the name “Chopper.” The biggest advantage of
chopper technology is the high-speed control of the
arc, similar to how inverter machines operate. Ablock
diagram for this is as follows:

In this system, current from a DC source such as the
MUL TI-SOURCE is applied through a solid state switch
to an inductor. By turning the switch on and of f, current

in the inductor and the arc can be controlled. The fol­lowing diagram depicts the current flow in the system
when the switch is open and closed:

When the switch is closed, current is applied through
the inductor to the arc. When the switch opens, current
stored in the inductor sustains flow in the arc and
through the diode. The repetition rate of switch closure
is 20Khz, which allows ultra-fast control of the arc. By

varying the ratio of on time versus off time of the switch
(Duty Cycle), the current applied to the arc is con­trolled. This is the basis for Chopper Technology:
Controlling the switch in such a way as to produce
superior welding.

E-9 E-9

THEORY OF OPERATION

MULTI-WELD 350

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EXTERNAL DC

SOURCE

INDUCTOR

AND DIODE

ARC

ARC

CONTROL

SOLID STATE

SWITCH

INDUCTOR

SWITCH

DIODE

ARC

CURRENT WITH SWITCH OPEN

CURRENT WITH SWITCH CLOSED

70-80VDC

E-10 E-10

NOTES

MULTI-WELD 350

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Troubleshooting & Repair Section......................................................................................Section F

How to Use Troubleshooting Guide ...........................................................................................F-2

PC Board Troubleshooting Procedures ......................................................................................F-3

Troubleshooting Guide ....................................................................................................F-4 - F-12

Test Procedures .......................................................................................................................F-13

Case Cover Assembly Removal and Replacement Procedure .........................................F-13

Power Module Capacitor Discharge Procedure ................................................................F-15

Input Contactor Coil Resistance and Supply Voltage Test .................................................F-17

Analog Control Power Supply PC Board Test ....................................................................F-20

DC Buss Power Supply PC Board Test..............................................................................F-23

Chopper PC Board Input Voltages and Resistance Tests..................................................F-26

Oscilloscope Waveforms ........................................................................................................ ..F-29

Normal Open Circuit Voltage Waveform (CC Mode) –

Input Voltage Applied 75 VDC ...........................................................................................F-29

Normal Open Circuit Voltage Waveform (CV Mode) –

Output Control at Maximum ................................................................................................F-30

Normal Weld Voltage Waveform (CC Stick Mode) –

Machine Loaded to 350 Amps at 34 Volts..........................................................................F-31

Normal Weld Voltage Waveform (CV Mode) –

Machine Loaded to 350 Amps at 34 Volts..........................................................................F-32

Normal Open Circuit Voltage Waveform (CV Mode) –

Output Control at Maximum ................................................................................................F-33

Replacement Procedures .........................................................................................................F-34

Case Front Assembly Removal and Replacement.............................................................F-34

Weld Control Board Removal and Replacement ...............................................................F-36

Amps/Volts Digital Meter and Potentiometer Removal and Replacement.........................F-39

Input Contactor Removal and Replacement.......................................................................F-42

Input Diode Removal and Replacement .............................................................................F-45

Fan Motor Assembly Removal and Replacement..............................................................F-48

Power Capacitor Removal and Replacement.....................................................................F-51

Chopper PC Board and Diode Module Removal and Replacement .................................F-54

Diode Module Removal and Replacement.........................................................................F-57

Retest After Repair ...................................................................................................................F-60

Section F-1 Section F-1

TABLE OF CONTENTS

- TROUBLESHOOTING & REPAIR SECTION -

MULTI-WELD 350

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This Troubleshooting Guide is provided to help
you locate and repair possible machine malfunc­tions. Simply follow the three-step procedure list­ed below.

Step 1. LOCATE PROBLEM (SYMPTOM). Look
under the column labeled “PROBLEM” (SYMP­TOMS). This column describes possible symp­toms that the machine may exhibit. Find the list­ing that best describes the symptom that the
machine is exhibiting. Symptoms are grouped
into four main categories: Output Problems,
Function Problems and Welding Problems.

Step 2. PERFORM EXTERNAL TESTS. The
second column, labeled “POSSIBLE AREAS OF
MISADJUSTMENT(S)”, lists the obvious external
possibilities that may contribute to the machine
symptom. Perform these tests/checks in the
order listed. In general, these tests can be con­ducted without removing the case cover.

Step 3. PERFORM COMPONENT TESTS. The
last column, labeled “Recommended Course of
Action” lists the most likely components that may
have failed in your machine. It also specifies the
appropriate test procedure to verify that the sub­ject component is either good or bad. If there are
a number of possible components, check the
components in the order listed to eliminate one
possibility at a time until you locate the cause of
your problem.

All of the referenced test procedures referred to in
the Troubleshooting Guide are described in detail
at the end of this section. Refer to the
Troubleshooting and Repair Table of Contents to
locate each specific Test Procedure. All of the
referred to test points, components, terminal
strips, etc., can be found on the referenced elec­trical wiring diagrams and schematics. Refer to
the Electrical Diagrams Section Table of Contents
to locate the appropriate diagram.

F-2 F-2

TROUBLESHOOTING & REPAIR

MULTI-WELD 350

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HOW TO USE TROUBLESHOOTING GUIDE

Service and repair should be performed by only Lincoln Electric Factory Trained Personnel.
Unauthorized repairs performed on this equipment may result in danger to the technician and machine
operator and will invalidate your factory warranty. For your safety and to avoid Electrical Shock, please
observe all safety notes and precautions detailed throughout this manual.

WARNING

CAUTION

If for any reason you do not understand the test procedures or are unable to perform the test/repairs
safely, contact the Lincoln Electric Service Department for electrical troubleshooting assistance before
you proceed. Call 1-800-833-9353.

ELECTRIC SHOCK can kill.

Have an electrician install and service
this equipment. Turn the machine OFF
before working on equipment. Do not

touch electrically hot parts.

Sometimes machine failures appear to be due to PC
board failures. These problems can sometimes be
traced to poor electrical connections. To avoid prob­lems when troubleshooting and replacing PC boards,
please use the following procedure:

1. Determine to the best of your technical ability that
the PC board is the most likely component causing
the failure symptom.

2. Check for loose connections at the PC board to
assure that the PC board is properly connected.

3. If the problem persists, replace the suspect PC
board using standard practices to avoid static elec­trical damage and electrical shock. Read the warn­ing inside the static resistant bag and perform the
following procedures:

PC Board can be damaged by
static electricity.

• Remove your body’s static charge
before opening the static-shielding
bag. Wear an anti-static wrist
strap. For safety, use a 1 Meg
ohm resistive cord connected to a
grounded part of the equipment
frame.

• If you don’t have a wrist strap,
touch an unpainted, grounded,
part of the equipment frame. Keep
touching the frame to prevent sta­tic build-up. Be sure not to touch
any electrically live parts at the
same time.

• Tools which come in contact with the PC Board must
be either conductive, anti-static or static-dissipative.

• Remove the PC Board from the static-shielding bag
and place it directly into the equipment. Don’t set the
PC Board on or near paper, plastic or cloth which
could have a static charge. If the PC Board can’t be
installed immediately, put it back in the static­shielding bag.

• If the PC Board uses protective shorting jumpers,
don’t remove them until installation is complete.

• If you return a PC Board to The Lincoln Electric
Company for credit, it must be in the static-shielding
bag. This will prevent further damage and allow prop­er failure analysis.

4. Test the machine to determine if the failure symp-

tom has been corrected by the replacement PC
board.

NOTE: Allow the machine to heat up so that all electri­cal components can reach their operating temperature.

5. Remove the replacement PC board and substitute

it with the original PC board to recreate the original
problem.

a. If the original problem does not reappear

by substituting the original board, then the
PC board was not the problem. Continue
to look for bad connections in the control
wiring harness, junction blocks, and termi­nal strips.

b. If the original problem is recreated by the

substitution of the original board, then the
PC board was the problem. Reinstall the
replacement PC board and test the
machine.

6. Always indicate that this procedure was followed

when warranty reports are to be submitted.

NOTE: Following this procedure and writing on the
warranty report, “INSTALLED AND SWITCHED PC
BOARDS TO VERIFY PROBLEM,” will help avoid
denial of legitimate PC board warranty claims.

F-3 F-3

TROUBLESHOOTING & REPAIR

MULTI-WELD 350

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Return to Master TOC Return to Master TOC Return to Master TOC Return to Master TOC

PC BOARD TROUBLESHOOTING PROCEDURES

WARNING

ATTENTION
Static-Sensitive
Devices
Handle only at
Static-Safe
Workstations

Reusable
Container
Do Not Destroy

Observe Safety Guidelines TROUBLESHOOTING GUIDE
detailed in the beginning of this manual.

CAUTION

If for any reason you do not understand the test procedures or are unable to perform the test/repairs safely,
contact the Lincoln Electric Service Department for electrical troubleshooting assistance before you proceed. Call
1-800-833-9353.

PROBLEMS
(SYMPTOMS)

POSSIBLE AREAS OF
MISADJUSTMENT(S)

RECOMMENDED
COURSE OF ACTION

OUTPUT PROBLEMS

Major physical or electrical damage is evident.

1. Contact your local Lincoln
Authorized Field Service
Facility.

1. Contact the Lincoln Electric
Service Department at 1-800­833-9353 (WELD)

The Multi-Weld 350 is completely
dead. The meters do not light and
the input contactor does not acti­vate when the ON/OFF Mode
Selector switch is turned on.

1. Make sure the power source is
working properly and supplying
at least 50VDC to the Multi­Weld 350. The electrode cable
must be positive polarity and the
work cable negative polarity.

2. Check the electrode and work
cables for loose or faulty con­nections.

1. Measure the input voltage to the
Multi-Weld 350. It must be
between 50 and 113VDC.

2. The ON/OFF Mode Selector
switch (S1) may be faulty.
Check and replace if faulty . See
the Wiring Diagram. Also check
associated wiring.

3. The input diode D1/D2 may be
open. Check. See the Wiring
Diagram.

4. Perform the DC Buss Supply

Board Test.

5. Perform the Analog Control
Power Supply Board Test.

6. The W eld Control Board may be
faulty. Replace.

F-4 F-4

TROUBLESHOOTING & REPAIR

MULTI-WELD 350

Return to Section TOC Return to Section TOC Return to Section TOC Return to Section TOC

Return to Master TOC Return to Master TOC Return to Master TOC Return to Master TOC

TROUBLESHOOTING GUIDE Observe Safety Guidelines

detailed in the beginning of this manual.

CAUTION

If for any reason you do not understand the test procedures or are unable to perform the test/repairs safely,
contact the Lincoln Electric Service Department for electrical troubleshooting assistance before you proceed. Call
1-800-833-9353.

PROBLEMS
(SYMPTOMS)

POSSIBLE AREAS OF
MISADJUSTMENT(S)

RECOMMENDED
COURSE OF ACTION

OUTPUT PROBLEMS

The meters light, but the input con­tactor does not activate when the
ON/OFF Mode Selector switch is
turned on. The Multi-Weld 350
does not have output.

1. Make sure the input voltage
applied to the Multi-Weld 350 is
not greater than 113VDC.

1. Check leads 330 and 303A for
loose or faulty connections.
See the Wiring Diagram.

2. Perform the Input Contactor

Coil Resistance and Supply
Voltage Test.

3. The Peripheral Board may be
faulty.

4. The W eld Control Board may be
faulty.

The Thermal Light is on. The Multi­Weld 350 does not have output.
The fan operates normally.

1. The output rating of the
machine may be exceeded.
See the Technical

Specifications.

2. Wait until the machine cools and
the Thermal Light goes out. The
machineís output should be
restored.

1. The Thermostat, located on the
input diode heat sink, may be
faulty.

2. Check leads 306, 307, 206, 207
and plugs J22 and J11 for loose
or faulty connections. See the
Wiring Diagram.

F-5 F-5

TROUBLESHOOTING & REPAIR

MULTI-WELD 350

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Return to Master TOC Return to Master TOC Return to Master TOC Return to Master TOC

Observe Safety Guidelines TROUBLESHOOTING GUIDE
detailed in the beginning of this manual.

CAUTION

If for any reason you do not understand the test procedures or are unable to perform the test/repairs safely,
contact the Lincoln Electric Service Department for electrical troubleshooting assistance before you proceed. Call
1-800-833-9353.

PROBLEMS
(SYMPTOMS)

POSSIBLE AREAS OF
MISADJUSTMENT(S)

RECOMMENDED
COURSE OF ACTION

OUTPUT PROBLEMS

The Multi-Weld 350 does not have output. The meters turn on, the input contactor activates and the Thermal light is off.

1. Check the welding cables for
loose or faulty connections.

1. Check for loose or faulty con­nections at the Control box, the
Chopper boards, and the
Analog Power Supply Board.
See the Wiring Diagram.

2. Check the heavy current carry­ing leads at the choke, the
chopper boards, the shunt and
the output terminals for loose or
faulty connections. See the
Wiring Diagram.

3. Perform the Chopper Board

Input Voltage and Resistance
Test.

4. Perform the Analog Control
Power Supply Board Test.

5. The W eld Control Board may be
faulty. Replace.

F-6 F-6

TROUBLESHOOTING & REPAIR

MULTI-WELD 350

Return to Section TOC Return to Section TOC Return to Section TOC Return to Section TOC

Return to Master TOC Return to Master TOC Return to Master TOC Return to Master TOC

TROUBLESHOOTING GUIDE Observe Safety Guidelines

detailed in the beginning of this manual.

CAUTION

If for any reason you do not understand the test procedures or are unable to perform the test/repairs safely,
contact the Lincoln Electric Service Department for electrical troubleshooting assistance before you proceed. Call
1-800-833-9353.

PROBLEMS
(SYMPTOMS)

POSSIBLE AREAS OF
MISADJUSTMENT(S)

RECOMMENDED
COURSE OF ACTION

FUNCTION PROBLEMS

The preset amps (CC mode) or volts (CV mode) are not adjustable.

1. The panel Output Control is dis­abled when a remote control
device is plugged into the 6-pin
remote receptacle.

1. The Output Control (R1) may be
faulty. Check or replace. Also
check associated leads for
loose or faulty connections.

2. Check all the plug connections
to the Weld Control Board for
loose or faulty connections.
See the Wiring Diagram.

3. The W eld Control Board may be
faulty. Replace.

The preset range is not correct. 1. The panel Output Control is dis-

abled when a remote control
device is plugged into the 6-pin
remote receptacle.

1. Make sure plug P3 is connected
securely to receptacle J3 on the
Weld Control Board. See the
Wiring Diagram. Make certain
all the jumper leads are in place.

2. Check all the plug connections
to the Weld Control Board for
loose or faulty connections.
See the Wiring Diagram.

3. The W eld Control Board may be
faulty. Replace.

F-7 F-7

TROUBLESHOOTING & REPAIR

MULTI-WELD 350

Return to Section TOC Return to Section TOC Return to Section TOC Return to Section TOC

Return to Master TOC Return to Master TOC Return to Master TOC Return to Master TOC

Observe Safety Guidelines TROUBLESHOOTING GUIDE
detailed in the beginning of this manual.

CAUTION

If for any reason you do not understand the test procedures or are unable to perform the test/repairs safely,
contact the Lincoln Electric Service Department for electrical troubleshooting assistance before you proceed. Call
1-800-833-9353.

PROBLEMS
(SYMPTOMS)

POSSIBLE AREAS OF
MISADJUSTMENT(S)

RECOMMENDED
COURSE OF ACTION

FUNCTION PROBLEMS

The meters do not light in either CV or CC modes.

1. In the CC mode, only the AMPS
meter will light. In the CV mode,
only the VOLTS meter will light.

1. Check all the plug connections
to the Weld Control Board for
loose or faulty connections.
See the Wiring Diagram.

2. Check the leads and connec­tions between the meters and
the Weld Control Board. See
the Wiring Diagram.

3. Perform the Analog Control

Power Supply Board Test.

4. The meters may be faulty.

5. The W eld Control Board may be
faulty. Replace.

One or both of the meter’s readings are not accurate.

1. Make sure the test or external
meter is reliable and accurate.

1. Check shunt feedback leads
R326, 327, R226, 227, plugs
P21 and P6 for loose or faulty
connections. See the Wiring
Diagram.

2. Check the integrity of lead 237
at plug P12 on the Weld Control
Board and also at plug P31 on
the Peripheral Board.

3. See the Digital Meter Calibra-
tion and Adjustment Test in
the Maintenance section.

4. Perform the Analog Control

Power Supply Board Test.

5. The W eld Control Board may be
faulty. Replace.

F-8 F-8

TROUBLESHOOTING & REPAIR

MULTI-WELD 350

Return to Section TOC Return to Section TOC Return to Section TOC Return to Section TOC

Return to Master TOC Return to Master TOC Return to Master TOC Return to Master TOC

TROUBLESHOOTING GUIDE Observe Safety Guidelines

detailed in the beginning of this manual.

CAUTION

If for any reason you do not understand the test procedures or are unable to perform the test/repairs safely,
contact the Lincoln Electric Service Department for electrical troubleshooting assistance before you proceed. Call
1-800-833-9353.

PROBLEMS
(SYMPTOMS)

POSSIBLE AREAS OF
MISADJUSTMENT(S)

RECOMMENDED
COURSE OF ACTION

FUNCTION PROBLEMS

The fan motor does not run when the machine is turned on.

1. Normal operation. The Multi­Weld 350 utilizes a Fan On
Demand system. The fan
should activate when welding.

1. Carefully check for approxi­mately 40VDC at the fan motor
leads (303+ to 300-). This test
must be performed while the
machine is connected to a resis­tive load or welding. If the
40VDC is NOT present, check
the associated leads and plugs
for loose or faulty connections.
See the Wiring Diagram. If the
correct voltage IS present and
the fan is not running, the fan
motor may be faulty.

2. If the correct voltage (40VDC) is
not present in the above test,
perform the DC Buss Supply

Board Test.

3. The W eld Control Board may be
faulty. Replace.

The fan does not run when welding. 1. The fan should turn on when the

arc starts and remain on for
about a minute after the arc is
out.

F-9 F-9

TROUBLESHOOTING & REPAIR

MULTI-WELD 350

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Observe Safety Guidelines TROUBLESHOOTING GUIDE
detailed in the beginning of this manual.

CAUTION

If for any reason you do not understand the test procedures or are unable to perform the test/repairs safely,
contact the Lincoln Electric Service Department for electrical troubleshooting assistance before you proceed. Call
1-800-833-9353.

PROBLEMS
(SYMPTOMS)

POSSIBLE AREAS OF
MISADJUSTMENT(S)

RECOMMENDED
COURSE OF ACTION

WELDING PROBLEMS

The welding output is high with no control.

1. Check all input and output
cables for shorts. Check the
positive input and output cables
for “grounded” connections to
the machine’s case.

1. Check shunt feedback leads
R326, 327, R226, 227, plugs
P21 and P6, for loose or faulty
connections. See the Wiring
Diagram.

2. Check the continuity of leads
401, 301, 201, plugs P20, P22
and P31. See the Wiring
Diagram.

3. Check the Output Control R1
and the associated leads. See
the Wiring Diagram.

4. The W eld Control Board may be
Faulty.

No control of welding output. 1. The panel Output Control is dis-

abled when a remote control
device is plugged into the 6-pin
remote receptacle.

2. Check the welding cables for
loose or faulty connections.

1. Check the Output Control (R1)
and the associated leads for
loose or faulty connections.

2. Check all the plug connections
to the Weld Control Board for
loose or faulty connections.
See the Wiring Diagram.

3. The W eld Control Board may be
faulty. Replace.

F-10 F-10

TROUBLESHOOTING & REPAIR

MULTI-WELD 350

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Return to Master TOC Return to Master TOC Return to Master TOC Return to Master TOC

TROUBLESHOOTING GUIDE Observe Safety Guidelines

detailed in the beginning of this manual.

CAUTION

If for any reason you do not understand the test procedures or are unable to perform the test/repairs safely,
contact the Lincoln Electric Service Department for electrical troubleshooting assistance before you proceed. Call
1-800-833-9353.

PROBLEMS
(SYMPTOMS)

POSSIBLE AREAS OF
MISADJUSTMENT(S)

RECOMMENDED
COURSE OF ACTION

WELDING PROBLEMS

When welding in the Stick Mode, the current changes with arc length.

1. Make sure the machine settings
are correct for the process
being used. When stick weld­ing, the CC Slope Switch (S2)
should be in the Stick/Gouge
position.

2. Check the welding cables for
loose or faulty connections.

1. Check the CC Slope Switch
(S2) and the associated lead
connections.

2. Check all the plug connections
to the Weld Control Board for
loose or faulty connections.
See the Wiring Diagram

3. The W eld Control Board may be
faulty. Replace.

When using “fast freeze” type elec­trodes such as E6010 or E7010,
the welding performance is poor.

1. Make sure the machine settings
are correct for the process
being used. When stick welding
with “fast freeze” type elec­trodes, the CC Slope Switch
(S2) should be in the Pipe posi­tion.

2. Check the welding cables for
loose or faulty connections.

1. Check the CC Slope Switch
(S2) and the associated lead
connections.

2. Check all the plug connections
to the Weld Control Board for
loose or faulty connections.
See the Wiring Diagram.

3. The W eld Control Board may be
faulty. Replace.

F-11 F-11

TROUBLESHOOTING & REPAIR

MULTI-WELD 350

Return to Section TOC Return to Section TOC Return to Section TOC Return to Section TOC

Return to Master TOC Return to Master TOC Return to Master TOC Return to Master TOC

Observe Safety Guidelines TROUBLESHOOTING GUIDE
detailed in the beginning of this manual.

CAUTION

If for any reason you do not understand the test procedures or are unable to perform the test/repairs safely,
contact the Lincoln Electric Service Department for electrical troubleshooting assistance before you proceed. Call
1-800-833-9353.

PROBLEMS
(SYMPTOMS)

POSSIBLE AREAS OF
MISADJUSTMENT(S)

RECOMMENDED
COURSE OF ACTION

WELDING PROBLEMS

The arc starting is not satisfactory. 1. The Hot Start Control may not

be set correctly for the process
being used.

2. Make sure the Output Control is
adjusted correctly for the
process being used.

1. Check the Hot Start Control
(R2) and associated leads and
connections. Note: The Arc
Force Control and Hot Start
Control are interchangeable and
may be switched to aid in trou­bleshooting. See the Wiring
Diagram.

2. The W eld Control Board may be
faulty.

When stick welding the electrode “stubs”.

1. The Arc Force Control may not
be set correctly for the process
being used. Increase the Arc
Force.

2. Make sure the Output Control is
adjusted correctly for the
process being used.

3. Check the welding cables for
loose or faulty connections.

1. Check the Arc Force Control
(R3) and associated leads and
connections. Note: The Arc
Force Control and Hot Start
Control are interchangeable and
may be switched to aid in trou­bleshooting. See the Wiring
Diagram.

2. The W eld Control Board may be
faulty.

F-12 F-12

TROUBLESHOOTING & REPAIR

MULTI-WELD 350

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TROUBLESHOOTING & REPAIR

F-13 F-13

MULTI-WELD 350

CASE COVER ASSEMBLY REMOVAL

AND REPLACEMENT PROCEDURE

WARNING

Service and repair should be performed by only Lincoln Electric factory trained personnel.
Unauthorized repairs performed on this equipment may result in danger to the technician
or machine operator and will invalidate your factory warranty . For your safety and to avoid
electrical shock, please observe all safety notes and precautions detailed throughout this
manual.

If for any reason you do not understand the test procedures or are unable to perform the
test/repairs safely, contact the Lincoln Electric Service Department for electrical trou­bleshooting assistance before you proceed. Call 1-800-833-9353 (WELD).

TEST DESCRIPTION

This procedure will aid the technician in the removal and replacement of the case sheet
metal cover.

MATERIALS NEEDED

3/8" Wrench or socket wrench

This procedure should take approximately 5 minutes to perform.

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Return to Master TOC Return to Master TOC Return to Master TOC Return to Master TOC

TROUBLESHOOTING & REPAIR

F-14 F-14

MULTI-WELD 350

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Return to Master TOC Return to Master TOC Return to Master TOC Return to Master TOC

MUL

TI-WELD 350

FIGURE F.1 – COVER REMOVAL DETAILS

CASE COVER ASSEMBLY REMOVAL

AND REPLACEMENT PROCEDURE (CONTINUED)

REMOVAL PROCEDURE

1. Set the CC/CV power switch to OFF.

2. Remove input power to the machine.

ELECTRIC SHOCK can kill.

Disconnect input power before removing the
case cover and performing tests or making
repairs to the machine.

3. Using the 3/8" nut driver, remove the 13
sheet metal screws holding the case cover
assembly in place.

4. Carefully lift the cover off the machine.

REPLACEMENT PROCEDURE

1. Be sure that the toroid rings on the top of
the tunnel assembly are lying flat and will
not restrict placement of the machine cover.
See Figure F.1.

2. The cover fits on in one direction only.
Verify front/back orientation, then carefully
lower the cover into place.

3. Install the 13 sheet metal screws that hold
the case cover in place.

WARNING

CASE COVER

TI-WELD 350

MUL

FRONT

TOROID
RING

SCREW
HOLE (13)

LOCATION

A

M

P

S

A

V

O

MULTI-WELD 350

CHOPPER TECHNOLOGY

L

T

S

V

ELECTRODE

WORK

LINCOLN

ELECTRIC

INPUT

TROUBLESHOOTING & REPAIR

F-15 F-15

MULTI-WELD 350

POWER MODULE CAPACITOR DISCHARGE PROCEDURE

WARNING

Service and repair should be performed by only Lincoln Electric factory trained personnel.
Unauthorized repairs performed on this equipment may result in danger to the technician
or machine operator and will invalidate your factory warranty . For your safety and to avoid
electrical shock, please observe all safety notes and precautions detailed throughout this
manual.

If for any reason you do not understand the test procedures or are unable to perform the
test/repairs safely, contact the Lincoln Electric Service Department for electrical trou­bleshooting assistance before you proceed. Call 1-800-833-9353 (WELD).

TEST DESCRIPTION

This procedure will insure that the large capacitor in each chopper power module has
been discharged. This procedure should be performed whenever work is to be attempt­ed on or near the power modules.

MATERIALS NEEDED

3/8" Wrench or socket wrench
Volt/Ohmmeter
Resistor (25-1000 ohms and 25 watts minimum)
Jumper leads

This procedure should take approximately 15 minutes to perform.

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TROUBLESHOOTING & REPAIR

F-16 F-16

MULTI-WELD 350

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Return to Master TOC Return to Master TOC Return to Master TOC Return to Master TOC

FIGURE F.2 – POWER MODULE CAPACITOR TERMINAL DISCHARGE

POWER MODULE CAPACITOR DISCHARGE PROCEDURE (CONTINUED)

PROCEDURE

1. Set the CC/CV power switch to OFF.

2. Remove input power to the machine.

ELECTRIC SHOCK can kill.

Disconnect input power before removing the
case cover and performing tests or making
repairs to the machine.

3. Perform the Case Cover Assembly
Removal procedure.

4. Locate the power module capacitors on the
right and left sides of the tunnel assembly.
See Figure F.2.

5. Using the resistor and jumper leads, CARE­FULLY discharge the capacitor terminals.

NEVER USE A SHORTING STRAP FOR
THIS PURPOSE. DO NOT TOUCH THE

TERMINALS WITH YOUR BARE HANDS.
Repeat the procedure for the second
capacitor.

6. Using the volt/ohmmeter, check the voltage
across the capacitor terminals. It should be
zero volts.

WARNING

AMPS

LINCOLN

INPUT

ELECTRIC

A

MULTI-WELD 350

CHOPPER TECHNOLOGY

VOL

TS

V

POWER
MODULE
CAPACITOR
TERMINALS

ELECTRODE

WORK

TROUBLESHOOTING & REPAIR

F-17 F-17

MULTI-WELD 350

INPUT CONTACTOR COIL RESISTANCE AND SUPPLY VOLTAGE TEST

WARNING

Service and repair should be performed by only Lincoln Electric factory trained personnel.
Unauthorized repairs performed on this equipment may result in danger to the technician
or machine operator and will invalidate your factory warranty . For your safety and to avoid
electrical shock, please observe all safety notes and precautions detailed throughout this
manual.

If for any reason you do not understand the test procedures or are unable to perform the
test/repairs safely, contact the Lincoln Electric Service Department for electrical trou­bleshooting assistance before you proceed. Call 1-800-833-9353 (WELD).

TEST DESCRIPTION

This test will determine if the input contactor is functioning properly.

MATERIALS NEEDED

Volt/Ohmmeter
3/8" Nut driver
Needle nose pliers
Wiring Diagram
External, isolated 40 VDC power supply

This procedure should take approximately 40 minutes to perform.

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TROUBLESHOOTING & REPAIR

F-18 F-18

MULTI-WELD 350

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FIGURE F.3 – INPUT CONTACTOR DETAILS

INPUT CONTACTOR COIL RESISTANCE AND

SUPPLY VOLTAGE TEST (CONTINUED)

COIL TEST PROCEDURE

1. Set the CC/CV power switch to OFF.

2. Remove input power to the machine.

ELECTRIC SHOCK can kill.

Disconnect input power before removing the
case cover and performing tests or making
repairs to the machine.

3. Perform the Case Cover Removal proce-
dure.

4. Perform the Power Module Capacitor
Discharge procedure.

5. Locate the input contactor and coil leads
#303A and #330. See Figure F.3.

6. Label and disconnect leads #303A and
#330 at their in-line connectors.

7. Check the coil resistance. Normal coil
resistance is approximately 100 ohms. If
the coil resistance is abnormally high or
low, the contactor may be faulty. Replace
the contactor.

8. Reconnect leads #303A and #330 to the
coil leads.

WARNING

LEADS
#303A
#330

TROUBLESHOOTING & REPAIR

F-19 F-19

MULTI-WELD 350

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INPUT CONTACTOR COIL RESISTANCE AND

SUPPLY VOLTAGE TEST (CONTINUED)

ELECTRIC SHOCK can kill.

With the input power ON, there are high volt­ages inside the machine. Do not reach into the
machine or touch any internal part of the
machine while power is on.

9. Carefully apply the correct input power to
the Multi-Weld 350 (50 – 113 VDC).

10. Set the Multi-Weld 350 to either CC or CV
mode. The contactor should activate. If it
does not, increase the input voltage but do
not exceed 113 VDC.

11. Carefully check for approximately 40 VDC
at leads #303A to #330. If the 40 VDC is
applied to the coil leads, the contactor
should activate.

12. If the reading is less than 40 VDC or not
present, perform the DC Buss Power

Supply PC Board Test.

13. Also check leads #303A, #330, #303, #403,
#230 and their associated plugs for loose or
faulty connections. See the Wiring
Diagram.

TEST FOR CONTACT CONTINUITY

1. Disconnect input power to the Multi-Weld

350.

ELECTRIC SHOCK can kill.

Disconnect input power before removing the
case cover and performing tests or making
repairs to the machine.

2. Perform the Power Module Capacitor
Discharge procedure.

3. Locate the input contactor and coil leads
#303A and #330. See Figure F.3.

4. Label and disconnect leads #303A and
#330 at their in-line connectors.

5. Using the external, isolated 40 VDC power
supply, carefully apply 40 VDC to the coil
leads. The contactor should activate.

6. With the contactor activated, check the con­tinuity across the large contacts. (Zero
ohms or very low resistance is normal.)
See Figure F.3. If the resistance is high,
the input contactor is faulty. Replace the
input contactor.

7. When the contactor is not activated, the
resistance should be infinite or very high
across the contacts. If the resistance is low,
the input contactor is faulty. Replace the
input contactor.

8. Remove the 40 VDC external supply and
reconnect the coil leads previously
removed.

9. If finished testing, perform the Case Cover
Replacement procedure.

WARNING

WARNING

TROUBLESHOOTING & REPAIR

F-20 F-20

MULTI-WELD 350

ANALOG CONTROL POWER SUPPLY PC BOARD TEST

WARNING

Service and repair should be performed by only Lincoln Electric factory trained personnel.
Unauthorized repairs performed on this equipment may result in danger to the technician
or machine operator and will invalidate your factory warranty . For your safety and to avoid
electrical shock, please observe all safety notes and precautions detailed throughout this
manual.

If for any reason you do not understand the test procedures or are unable to perform the
test/repairs safely, contact the Lincoln Electric Service Department for electrical trou­bleshooting assistance before you proceed. Call 1-800-833-9353 (WELD).

TEST DESCRIPTION

This test will determine if the Analog Control Power Supply PC Board is receiving and
passing the proper signal voltages.

MATERIALS NEEDED

3/8" Nut driver
Analog Volt/Ohmmeter
Wiring Diagram

This procedure should take approximately 30 minutes to perform.

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TROUBLESHOOTING & REPAIR

F-21 F-21

MULTI-WELD 350

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FIGURE F.4 – ANALOG CONTROL POWER SUPPLY PC BOARD

ANALOG CONTROL POWER SUPPLY PC BOARD TEST (CONTINUED)

TEST PROCEDURE

1. Set the CC/CV power switch to OFF.

2. Remove input power to the machine.

ELECTRIC SHOCK can kill.

Disconnect input power before removing the
case cover and performing tests or making
repairs to the machine.

3. Perform the Case Cover Removal proce-
dure.

4. Perform the Power Module Capacitor
Discharge procedure.

5. Locate the Analog Control Power Supply
PC Board and plugs P41 and P42. See
Figure F.4.

6. Carefully apply the correct input power to
the Multi-Weld 350 (50 – 113 VDC).

7. Set the Multi-Weld 350 to either CC or CV
mode. Make sure the input contactor acti­vates. If it does not, increase the input volt­age but do not exceed 113 VDC. The LED
on the DC Buss Power Supply PC Board
should light.

8. Check the Analog Control Power Supply PC
Board input and output voltages according
to Table F.1. See Figure F.4 and the Wiring
Diagram.

WARNING

P41

1 2

3 4

1 2 3 4 5

6 7 8 9 10

AMPS

A

LINCOLN

ELECTRIC

MULTI-WELD 350

INPUT

CHOPPER TECHNOL OGY

P42

V

WORK

VOLTS

ELECTRODE

P42

P41

ANALOG
CONTROL
POWER
SUPPLY
PC BOARD

TROUBLESHOOTING & REPAIR

F-22 F-22

MULTI-WELD 350

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TABLE F.1

ANALOG CONTROL POWER SUPPLY PC BOARD VOLTAGE TABLE

Positive Meter Probe Negative Meter Probe Acceptable Voltage

Conditions/Comments

Test Point Test Point Reading

Plug P41 – Pin 1 Plug P41 – Pin 2 38.0 – 42.0 VDC

Supply from DC Buss
Power Supply Board

Plug P42 – Pin 1 Plug P42 – Pin 6 18.0 – 21.0 VDC

Supply for right side
Chopper PC Board

Plug P42 – Pin 3 Plug P42 – Pin 8 18.0 – 21.0 VDC

Supply for left side
Chopper PC Board

Plug P42 – Pin 10 Plug P42 – Pin 4 14.0 – 16.0 VDC

+15 VDC Supply to
Peripheral Board

Plug P42 – Pin 5 Plug P42 – Pin 7 14.0 – 16.0 VDC

+15 VDC Supply to
Weld Control Board

Plug P42 – Pin 2 Plug P42 – Pin 7 4.5 – 5.5 VDC

+5 VDC Supply to
Weld Control Board

Plug P42 – Pin 9 Plug P42 – Pin 7 -14.0 – 16.0 VDC

-15 VDC Supply to
Weld Control Board

ANALOG CONTROL POWER SUPPLY PC BOARD TEST (CONTINUED)

9. If all the voltages are correct, the Analog
Control Power Supply PC Board is operat­ing properly.

10. If any of the output voltages are not correct
and the input voltage is correct, the Analog
Control Power Supply PC Board may be
faulty.

11. If the input voltage is not correct, check
leads #436, #437 and their associated
plugs for loose or faulty connections. See
the Wiring Diagram. Perform the DC Buss

Power Supply PC Board Test.

12. If finished testing, perform the Case Cover
Replacement procedure.

TROUBLESHOOTING & REPAIR

F-23 F-23

MULTI-WELD 350

DC BUSS POWER SUPPLY PC BOARD TEST

WARNING

Service and repair should be performed by only Lincoln Electric factory trained personnel.
Unauthorized repairs performed on this equipment may result in danger to the technician
or machine operator and will invalidate your factory warranty . For your safety and to avoid
electrical shock, please observe all safety notes and precautions detailed throughout this
manual.

If for any reason you do not understand the test procedures or are unable to perform the
test/repairs safely, contact the Lincoln Electric Service Department for electrical trou­bleshooting assistance before you proceed. Call 1-800-833-9353 (WELD).

TEST DESCRIPTION

This test will determine if the DC Buss Power Supply PC Board is receiving and process­ing the proper signal voltages.

MATERIALS NEEDED

3/8" Nut driver
Analog Volt/Ohmmeter
Wiring Diagram

This procedure should take approximately 30 minutes to perform.

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TROUBLESHOOTING & REPAIR

F-24 F-24

MULTI-WELD 350

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FIGURE F.5 – DC BUSS POWER SUPPLY PC BOARD

DC BUSS POWER SUPPLY PC BOARD TEST(CONTINUED)

TEST PROCEDURE

1. Set the CC/CV power switch to OFF.

2. Remove input power to the machine.

ELECTRIC SHOCK can kill.

Disconnect input power before removing the
case cover and performing tests or making
repairs to the machine.

3. Perform the Case Cover Removal proce-

dure.

4. Perform the Power Module Capacitor
Discharge procedure.

5. Locate the DC Buss Power Supply PC
Board and plugs P46 and P47. See Figure
F.5.

6. Carefully apply the correct input power to
the Multi-Weld 350 (50 – 113 VDC).

7. Set the Multi-Weld 350 to either CC or CV
mode. Make sure the input contactor acti­vates. If it does not, increase the input volt­age but do not exceed 113 VDC. The LED
on the DC Buss Power Supply PC Board
should light.

WARNING

P46

P47

1 2 1 2 3 4

5 6 7 8 3 4

AMPS

INPUT

LINCOLN

ELECTRIC

A

MULTI-WELD 350

CHOPPER TECHNOLOGY

VOL

TS

V

ELECTRODE

WORK

P46

P47

DC BUSS
POWER
SUPPLY
PC BOARD

TROUBLESHOOTING & REPAIR

F-25 F-25

MULTI-WELD 350

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DC BUSS POWER SUPPLY PC BOARD TEST(CONTINUED)

8. Check the DC Buss Power Supply PC
Board input and output voltages according
to Table F.2. See Figure F.5 and the
Wiring Diagram.

9. If all the voltages are correct, the DC Buss
Power Supply PC Board is operating prop­erly.

10. If any of the output voltages are not correct
and the input voltage is correct, the DC
Buss Supply Board may be faulty.

11. If the input voltage is not correct, check
leads #401A, #402, #302, #202, #231 and
the On/Off mode switch (SW1). See the
Wiring Diagram.

NOTE: The input voltage to the DC Buss Power
Supply PC Board should be the same as the
input voltage applied to the Multi-Weld 350.

12. If finished testing, perform the Case Cover
Replacement procedure.

TABLE F.2

DC BUSS POWER SUPPLY PC BOARD VOLTAGE TABLE

Positive Meter Probe Negative Meter Probe Acceptable Voltage

Conditions/Comments

Test Point Test Point Reading

Plug P46 – Pin 1 Plug P46 – Pin 3 50 – 113 VDC

Should be same as input
voltage supplied to
Multi-Weld 350

Plug P47 – Pin 7 Plug P47 – Pin 1 38.0 – 42.0 VDC

Supply to Analog Control
Power Supply PC Board

Plug P47 – Pin 8 Plug P47 – Pin 6 38.0 – 42.0 VDC

Supply for Fan and Input
Contactor

Plug P47 – Pin 4 Plug P47 – Pin 6 38.0 – 42.0 VDC

Output to Peripheral
Board

TROUBLESHOOTING & REPAIR

F-26 F-26

MULTI-WELD 350

CHOPPER PC BOARD INPUT VOLTAGES AND RESISTANCE TEST

WARNING

Service and repair should be performed by only Lincoln Electric factory trained personnel.
Unauthorized repairs performed on this equipment may result in danger to the technician
or machine operator and will invalidate your factory warranty . For your safety and to avoid
electrical shock, please observe all safety notes and precautions detailed throughout this
manual.

If for any reason you do not understand the test procedures or are unable to perform the
test/repairs safely, contact the Lincoln Electric Service Department for electrical trou­bleshooting assistance before you proceed. Call 1-800-833-9353 (WELD).

TEST DESCRIPTION

This test will determine if there are shorted IGBTs or Chopper PC Boards. This test will
also verify that the Chopper PC Boards are receiving the correct operating voltages.

MATERIALS NEEDED

Volt/Ohmmeter
3/8"Nut driver
7/16" Wrench
Wiring Diagram

This procedure should take approximately 50 minutes to perform.

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TROUBLESHOOTING & REPAIR

F-27 F-27

MULTI-WELD 350

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FIGURE F.6 – POWER MODULE ASSEMBLY DETAILS

CHOPPER PC BOARD INPUT VOLTAGES AND

RESISTANCE TEST (CONTINUED)

TEST PROCEDURE

1. Set the CC/CV power switch to OFF.

2. Remove input power to the machine.

ELECTRIC SHOCK can kill.

Disconnect input power before removing the
case cover and performing tests or making
repairs to the machine.

3. Perform the Case Cover Removal proce-
dure.

4. Perform the Power Module Capacitor
Discharge procedure.

WARNING

CLAMP

P45/45A

1 2 3

4 5 6

BRACKET

IGBT
HEAT
SINK

AMPS

A

LINCOLN

ELECTRIC

MULTI-WELD 350

INPUT

CHOPPER TECHNOLOGY

DIODE
MODULE
D3

REMOVE CASE
BACK PANEL
TO ACCESS
HEAT SINK
TEST POINT
(4 SCREWS)

+

-

COPPER

VOLTS

V

DIODE
D5

ELECTRODE

WORK

CAPACITOR
POSITIVE
STRAP

COPPER
CAPACITOR
NEGATIVE
STRAP
LEADS
#X1
#X4
#401
#401A

TROUBLESHOOTING & REPAIR

F-28 F-28

MULTI-WELD 350

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CHOPPER PC BOARD INPUT VOLTAGES AND

RESISTANCE TEST (CONTINUED)

Test Procedure for the Left Side
Power Module

1. Locate the Power Module Capacitor termi­nals. Using the 7/16" wrench, disconnect
leads #X1, #X4, #401, #401A and the cop­per straps. Carefully electrically isolate
these leads and straps from the capacitor
terminals and heat sink assembly. See

Figure F.6.

2. Using the 3/8" nut driver, remove the four
screws holding the case back to the tunnel
assembly. This will provide access to the
IGBT heat sinks.

3. Using the analog ohmmeter, connect the
positive meter probe to the positive copper
strap and the negative meter probe to the
IGBT heat sink. (This is the inner heat
sink.) See Figure F.6 for test point loca-
tions. The resistance should be very high
(over 20,000 ohms). If the resistance is
low, then either the IGBT is shorted or the
diode D5 is shorted. Disconnect the small
D5 cathode lead to isolate the problem. It
is possible that both devices may be faulty.

4. Reverse the meter leads. The resistance
should be low (approximately 100 ohms). If
the resistance is high, the diode D5 may be
open.

5. Using the analog ohmmeter, check diode
module D3. Connect the negative meter
probe to the negative copper strap connect­ed to the diode module and the positive
probe to the heat sink. See Figure F.6 for
the test point locations. The resistance
should be very high (over 20,000 ohms). If
the resistance is low, the diode module D3
may be shorted.

6. Reverse the meter leads. The resistance
should be low (approximately 100 ohms). If
the resistance is high, the diode module D3
may be open.

7. Repeat Steps 1 through 5 for the Right
Side Power Module. See the Wiring
Diagram.

8. Replace all leads previously removed. See
Figure F.6 and the Wiring Diagram. Torque
the capacitor bolts to 50 to 60 inch pounds.

CHOPPER PC BOARD VOLTAGE
TESTS FOR BOTH LEFT AND
RIGHT SIDES

1. Locate Plug P45(A) and disconnect it from
J45(A). See Figure F.6.

ELECTRIC SHOCK can kill.

With the input power ON, there are high volt­ages inside the machine. Do not reach into the
machine or touch any internal part of the
machine while power is on.

2. Carefully apply the correct input voltage to
the Multi-Weld 350 (50 – 113 VDC). The
machine should be in the CC mode and the
CC Slope switch should be in the
Stick/Gouge position.

3. Turn the machine on and carefully check for

18.0 – 21.0 VDC at P45(A) pin 1 (+) to
P45(A) pin 3 (-). This is the 20 VDC supply
from the Analog Control Power Supply PC
Board to the Chopper PC Board.

NOTE: Be careful not to touch the capacitor
terminals.

4. Also carefully check for 11.0 – 14.0 VDC at
P45(A) pin 7 (+) to P45(A) pin 9 (-). This is
the Pulse Width Modulation Signal from the
Weld Control Board to the Chopper PC
board.

5. If any of the voltages are not present, check
associated leads and plugs for loose or
faulty connections. See the Wiring
Diagram.

6. Remove the input power and perform the

Power Module Capacitor Discharge

Procedure.

7. Reconnect the plugs previously discon­nected.

8. If finished testing, perform the Case Cover
Replacement procedure.

WARNING

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TROUBLESHOOTING & REPAIR

F-29 F-29

MULTI-WELD 350

This is the typical CC open circuit out­put voltage generated from a properly
operating machine. Note that each
vertical division represents 50 volts
and that each horizontal division rep­resents 5 µs in time.

SCOPE SETTINGS

Volts/Div.....................50V/Div.

Horizontal Sweep......5 µs/Div.

Coupling.............................DC

Trigger.........................Internal

NORMAL OPEN CIRCUIT VOLTAGE WAVEFORM

CC MODE – INPUT VOLTAGE APPLIED 75 VDC

0 volts0 volts

50V 5µs

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TROUBLESHOOTING & REPAIR

F-30 F-30

MULTI-WELD 350

This is the typical CV output voltage
generated from a properly operating
machine. Note that each vertical
division represents 50 volts and that
each horizontal division represents
5 µs in time.

SCOPE SETTINGS

Volts/Div.....................50V/Div.

Horizontal Sweep......5 µs/Div.

Coupling.............................DC

Trigger.........................Internal

NORMAL OPEN CIRCUIT VOLTAGE WAVEFORM

CV MODE – OUTPUT CONTROL AT MAXIMUM

0 volts

0 volts

50V 5µs

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TROUBLESHOOTING & REPAIR

F-31 F-31

MULTI-WELD 350

This is the typical CC output voltage
generated from a properly operating
machine. Note that each vertical divi­sion represents 50 volts and that each
horizontal division represents 50µs in
time.

The machine was loaded with a resis­tance grid bank to 350 amps at 34
volts.

SCOPE SETTINGS

Volts/Div.....................50V/Div.

Horizontal Sweep.....50µs/Div.

Coupling.............................DC

Trigger.........................Internal

NORMAL WELD VOLTAGE WAVEFORM

MACHINE LOADED TO 350 AMPS AT 34 VOLTS – CC-STICK MODE

0 volts

50V 50µs

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TROUBLESHOOTING & REPAIR

F-32 F-32

MULTI-WELD 350

NORMAL WELD VOLTAGE WAVEFORM

MACHINE LOADED TO 350 AMPS AT 34 VOLTS – CV MODE

This is the typical CV output voltage
generated from a properly operating
machine. Note that each vertical divi­sion represents 50 volts and that each
horizontal division represents 50µs in
time.

The machine was loaded with a resis­tance grid bank to 350 amps at 34
volts.

SCOPE SETTINGS

Volts/Div.....................50V/Div.

Horizontal Sweep.....50µs/Div.

Coupling.............................DC

Trigger.........................Internal

50V 50µs

0 volts

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TROUBLESHOOTING & REPAIR

F-33 F-33

MULTI-WELD 350

This is the typical CV open circuit out­put voltage generated from a properly
operating machine. Note that each
vertical division represents 50 volts
and that each horizontal division rep­resents 1 millisecond in time.

SCOPE SETTINGS

Volts/Div.....................50V/Div.

Horizontal Sweep.....1 ms/Div.

Coupling.............................DC

Trigger.........................Internal

NORMAL OPEN CIRCUIT VOLTAGE WAVEFORM

CV MODE – OUTPUT CONTROL AT MINIMUM

0 volts

0 volts

50V 1ms

TROUBLESHOOTING & REPAIR

F-34 F-34

MULTI-WELD 350

CASE FRONT ASSEMBLY REMOVAL AND REPLACEMENT

WARNING

Service and repair should be performed by only Lincoln Electric factory trained personnel.
Unauthorized repairs performed on this equipment may result in danger to the technician
or machine operator and will invalidate your factory warranty . For your safety and to avoid
electrical shock, please observe all safety notes and precautions detailed throughout this
manual.

If for any reason you do not understand the test procedures or are unable to perform the
test/repairs safely, contact the Lincoln Electric Service Department for electrical trou­bleshooting assistance before you proceed. Call 1-800-833-9353 (WELD).

DESCRIPTION

The following procedure will aid the technician in removing and replacing the case front
assembly on the Multi-Weld 350.

MATERIALS NEEDED

3/8" Nut driver, wrench or socket wrench
Wiring Diagram

This procedure should take approximately 15 minutes to perform.

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TROUBLESHOOTING & REPAIR

F-35 F-35

MULTI-WELD 350

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FIGURE F.7 – CASE FRONT ASSEMBLY REMOVAL

CASE FRONT ASSEMBLY REMOVAL AND REPLACEMENT (CONTINUED)

REMOVAL PROCEDURE

1. Set the CC/CV power switch to OFF.

2. Remove input power to the machine.

ELECTRIC SHOCK can kill.

Disconnect input power before removing the
case cover and performing tests or making
repairs to the machine.

3. Perform the Case Cover Assembly
Removal procedure.

4. Perform the Power Capacitor Discharge
procedure.

5. Label and disconnect the three wiring har­ness plug assemblies that connect to the
case front assembly. See Figure F.7 and
the Wiring Diagram.

6. Carefully turn the machine onto its side.
See Figure F.7 for location.

7. Using the 3/8" nut driver, remove the two
screws holding the case front assembly to
the machine base. Support the case front
assembly as you remove the second screw.

8. Carefully remove the case front assembly
and set the machine back upright.

REPLACEMENT PROCEDURE

1. Carefully turn the machine onto its side.

2. Position the case front assembly on the
base and attach it with two screws previ­ously removed.

3. Set the machine back upright. Connect the
three wiring harness plug assemblies.

4. Replace the case cover.

WARNING

PLUG
ASSEMBLIES
(3)

AMPS

A

MULTI-WELD 350

CHOPPER TECHNOLOGY

VOLTS

V

ELECTRODE

WORK

LINCOLN

ELECTRIC

INPUT

BASE SCREWS (2)
ACCESS FROM
BOTTOM

TROUBLESHOOTING & REPAIR

F-36 F-36

MULTI-WELD 350

WELD CONTROL OR PERIPHERAL PC BOARD

REMOVAL AND REPLACEMENT

WARNING

Service and repair should be performed by only Lincoln Electric factory trained personnel.
Unauthorized repairs performed on this equipment may result in danger to the technician
or machine operator and will invalidate your factory warranty . For your safety and to avoid
electrical shock, please observe all safety notes and precautions detailed throughout this
manual.

If for any reason you do not understand the test procedures or are unable to perform the
test/repairs safely, contact the Lincoln Electric Service Department for electrical trou­bleshooting assistance before you proceed. Call 1-800-833-9353 (WELD).

DESCRIPTION

The following procedure will aid the technician in removing and replacing the Weld Control
or Peripheral PC Board on the Multi-Weld 350.

MATERIALS NEEDED

3/8" Nut driver, wrench or socket wrench
5/16" Nut driver
Wiring Diagram

This procedure should take approximately 30 minutes to perform.

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TROUBLESHOOTING & REPAIR

F-37 F-37

MULTI-WELD 350

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FIGURE F.8 – CASE FRONT ASSEMBLY DETAILS

WELD CONTROL OR PERIPHERAL PC BOARD

REMOVAL AND REPLACEMENT (CONTINUED)

REMOVAL PROCEDURE

Refer to Figure F.8.

1. Set the CC/CV power switch to OFF.

2. Remove input power to the machine.

ELECTRIC SHOCK can kill.

Disconnect input power before removing the
case cover and performing tests or making
repairs to the machine.

3. Perform the Case Cover Assembly
Removal procedure.

4. Perform the Power Capacitor Discharge
procedure.

5. Perform the Case Front Assembly
Removal procedure.

6. Using the 5/16" nut driver, remove the
seven screws from the control box rear
panel.

WARNING

PLUG P31

PERIPHERAL
PC BOARD

JUMPER

AMPS

LINCOLN

ELECTRIC

4

5

3

6

2

7

4 4

8

0

6 6

HOT START ARC FORCE

9

10

8

INPUT

CC

OFF

A

V

MULTI-WELD 350

2

0

2

10

8

10

OTE

CHOPPER TECHNOLOGY

WORK

CV

VOLTS

STICK 7018
GOUGE

PIPE

SLOPE

ELECTRODE

PLUG P3

NUTS

L11141-2

CC

WELD
CONTROL
PC BOARD

SCREWS
(7)

TROUBLESHOOTING & REPAIR

F-38 F-38

MULTI-WELD 350

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WELD CONTROL OR PERIPHERAL PC BOARD

REMOVAL AND REPLACEMENT (CONTINUED)

7. Carefully label and remove the 12 molex
plugs from the Weld Control PC board.
Press and hold the keeper on each plug as
you remove it. Also remove plug P31 from
the Peripheral PC Board as shown in
Figure F.8. This will allow the assembly to
lie flat.

8. Using the 3/8" nut driver, remove the four
nuts holding the Weld Control PC Board in
place.

NOTE: Verify the orientation of the Weld Con­trol PC Board for replacement. You may need
to remove a nut on the Peripheral PC Board in
order to free the Weld Control PC Board.

9. Carefully remove the Weld Control PC
Board.

NOTE: It may be necessary to pry gently on the
PC Board to remove it.

REPLACEMENT PROCEDURE

1. Set the Weld Control PC Board squarely
onto the studs and press it in place. Verify
proper orientation. Replace any nuts
removed from the Peripheral PC Board at
disassembly.

2. Tighten the four 3/8" nuts holding the board
in place.

3. Attach the molex plugs, including the plug
removed from the Peripheral PC Board at
disassembly. See the Wiring Diagram.

NOTE: Make sure jumper plug P3 is in place.

4. Attach the rear panel with seven 5/16"
screws.

5. Perform the Case Front Assembly
Replacement procedure.

6. Perform the Case Cover Assembly
Replacement procedure.

TROUBLESHOOTING & REPAIR

F-39 F-39

MULTI-WELD 350

AMPS/VOLTS DIGITAL METER AND POTENTIOMETER

REMOVAL AND REPLACEMENT

WARNING

Service and repair should be performed by only Lincoln Electric factory trained personnel.
Unauthorized repairs performed on this equipment may result in danger to the technician
or machine operator and will invalidate your factory warranty . For your safety and to avoid
electrical shock, please observe all safety notes and precautions detailed throughout this
manual.

If for any reason you do not understand the test procedures or are unable to perform the
test/repairs safely, contact the Lincoln Electric Service Department for electrical trou­bleshooting assistance before you proceed. Call 1-800-833-9353 (WELD).

DESCRIPTION

The following procedure will aid the technician in removing and replacing the Amps or
Volts Digital Meter or the Output Control potentiometer on the Multi-Weld 350.

MATERIALS NEEDED

3/8" Nut driver, wrench or socket wrench
5/16" Nut driver
Phillips screw driver
Allen head wrench
Diagonal cutters
Wiring Diagram

This procedure should take approximately 30 minutes to perform.

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TROUBLESHOOTING & REPAIR

F-40 F-40

MULTI-WELD 350

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FIGURE F.9 – DIGITAL METER AND POTENTIOMETER DETAILS

AMPS/VOLTS DIGITAL METER AND POTENTIOMETER

REMOVAL AND REPLACEMENT (CONTINUED)

DIGITAL METER REMOVAL
PROCEDURE

Refer to Figure F.9.

1. Set the CC/CV power switch to OFF.

2. Remove input power to the machine.

ELECTRIC SHOCK can kill.

Disconnect input power before removing the
case cover and performing tests or making
repairs to the machine.

3. Perform the Case Cover Assembly
Removal procedure.

4. Perform the Power Capacitor Discharge
procedure.

5. Perform the Case Front Assembly
Removal procedure.

6. Using the 5/16" nut driver, remove the
seven screws from the control box rear
panel.

WARNING

DIGITAL
METER

KNOB

2

3

4

HOT START

5

INPUT

LINCOLN

ELECTRIC

6

10

7

8

9

AMPS

6 6

LENS

BEZEL

SPACER

SEAL

CC

OFF

A

MULTI-WELD 350

2

0

4 4

2

ARC FORCE

10

OTE

CHOPPER

TECHNOLOGY

WORK

CV

OUTPUT
CONTROL
POTENTIOMETER

VOLTS

V

STICK 7018
GOUGE

L11141-2

PIPE

CC

SLOPE

ELECTR

ODE

TROUBLESHOOTING & REPAIR

F-41 F-41

MULTI-WELD 350

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AMPS/VOLTS DIGITAL METER AND POTENTIOMETER

REMOVAL AND REPLACEMENT (CONTINUED)

7. Carefully remove the Amps or Volts Digital
Meter molex plug from the Weld Control
PC Board. Press and hold the keeper on
the plug as you remove it.

8. Using the 5/16" nut driver, remove the two
nuts and flat washers holding the Amps or
Volts Digital Meter in place.

9. Using the phillips screw driver, remove the
two screws holding the bezel and lens (and
the meter) to the front panel.

10. Carefully remove the Amps or Volts Digital
Meter. Do not damage the gasket.

REPLACEMENT PROCEDURE

1. Fit the meter into position, adjustable slot
side down. Verify that the gasket is in place.

2. Insert the two phillips screws through the
bezel, and with the lens in place, tighten
the screws into the meter.

3. Install the flat washers and 5/16" nuts onto
the screws and tighten them.

4. Attach the molex plug to the Weld Control
PC Board. See the Wiring Diagram.

5. Attach the rear panel with seven 5/16"
screws.

6. Perform the Case Front Assembly
Replacement procedure.

7. Perform the Case Cover Assembly
Replacement procedure.

OUTPUT CONTROL POTENTIOMETER
REMOV AL PROCEDURE

Refer to Figure F.9.

1. Set the CC/CV power switch to OFF.

2. Remove input power to the machine.

ELECTRIC SHOCK can kill.

Disconnect input power before removing the
case cover and performing tests or making
repairs to the machine.

3. Perform the Case Cover Assembly
Removal procedure.

4. Perform the Power Capacitor Discharge
procedure.

5. Perform the Case Front Assembly
Removal procedure.

6. Using the 5/16" nut driver, remove the
seven screws from the control box rear
panel.

7. Carefully remove the potentiometer molex
plug from the Weld Control PC Board.
Press and hold the keeper on the plug as
you remove it.

8. Using the diagonal cutters, cut the cable tie
holding the potentiometer to the back
panel.

9. Using the allen wrench, remove the set
screw holding the potentiometer knob to
the shaft.

10. Remove the knob, shaft seal, and spacer.
Pull the potentiometer out from the panel.

REPLACEMENT PROCEDURE

1. Fit the potentiometer into position, verifying
proper orientation. Install a new cable tie.

2. Install the spacer, shaft seal, and knob.

3. Tighten the knob onto the shaft with the set
screw.

4. Attach the molex plug to the Weld Control
PC Board. See the Wiring Diagram.

5. Attach the rear panel with seven 5/16"
screws.

6. Perform the Case Front Assembly
Replacement procedure.

7. Perform the Case Cover Assembly
Replacement procedure.

WARNING

TROUBLESHOOTING & REPAIR

F-42 F-42

MULTI-WELD 350

INPUT CONTACTOR REMOVAL AND REPLACEMENT

WARNING

Service and repair should be performed by only Lincoln Electric factory trained personnel.
Unauthorized repairs performed on this equipment may result in danger to the technician
or machine operator and will invalidate your factory warranty . For your safety and to avoid
electrical shock, please observe all safety notes and precautions detailed throughout this
manual.

If for any reason you do not understand the test procedures or are unable to perform the
test/repairs safely, contact the Lincoln Electric Service Department for electrical trou­bleshooting assistance before you proceed. Call 1-800-833-9353 (WELD).

DESCRIPTION

The following procedure will aid the technician in removing and replacing the input con­tactor on the Multi-Weld 350.

MATERIALS NEEDED

3/8" Nut driver, wrench or socket wrench
17 mm Wrench or socket wrench
Diagonal cutters
Wiring Diagram

This procedure should take approximately 30 minutes to perform.

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TROUBLESHOOTING & REPAIR

F-43 F-43

MULTI-WELD 350

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FIGURE F.10 – INPUT CONTACTOR ASSEMBLY DETAILS

INPUT CONTACTOR REMOVAL AND REPLACEMENT (CONTINUED)

REMOVAL PROCEDURE

Refer to Figure F.10.

1. Set the CC/CV power switch to OFF.

2. Remove input power to the machine.

ELECTRIC SHOCK can kill.

Disconnect input power before removing the
case cover and performing tests or making
repairs to the machine.

3. Perform the Case Cover Assembly
Removal procedure.

4. Perform the Power Capacitor Discharge
procedure.

5. Perform the Case Front Assembly
Removal procedure.

6. Label and disconnect leads #330 and
#303A at their in-line connectors. Cut any
necessary cable ties.

WARNING

LEAD #331

COPPER
STRAP

LEADS
#X1A
#X1
#XBP5

INPUT
CONTACTOR

LEADS
#303A
#330

BASE
BOLTS (2)

INPUT DIODE
HEAT SINK

HEAT SINK
BOLTS & NYLON
INSULATORS (2)

TROUBLESHOOTING & REPAIR

F-44 F-44

MULTI-WELD 350

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INPUT CONTACTOR REMOVAL AND REPLACEMENT (CONTINUED)

7. Using the 17 mm wrench, remove the nuts
from the input contactor terminal closest to
the machine front. Label the leads and
note their placement: bottom nut (not
removed), lead #X1A, Lead #X1, lead
#BP5.

NOTE: The top nut has grooves on the side that
faces up.

8. Using the 17 mm wrench, remove the nuts
from the other input contactor terminal.
Bottom nut (not removed), copper contac­tor strap, center nut, lead #331, top nut.

NOTE: The top nut has grooves on the side that
faces up.

9. With the 3/8" socket wrench, remove the
two bolts and nylon insulators holding the
input contactor to the input diode heat sink.

NOTE: The mylar insulation sheet fits between
the nylon insulators at replacement.

10. Using the 3/8" socket wrench, remove the
two screws holding the input contactor to
the machine base.

11. Carefully remove the input contactor.

REPLACEMENT PROCEDURE

1. Set the input contactor onto the machine
base and install two 3/8" screws in the base
mounting holes.

2. Install the two sets of 3/8" bolts and nylon
insulators, along with the mylar insulation
sheet, to the input diode heat sink. The
mylar sheet fits between the nylon insula­tors under the mounting bracket.

3. Install the copper contactor strap and lead
#331 to the input contactor rear terminal.
See Figure F.10.

4. Install leads #X1A, X1, and #BP5 to the
input contactor front terminal. See Figure
F.10. Be sure the top nut on each terminal
is the grooved nut, with the grooves facing
up.

5. Connect leads #330 and #303A at their in­line connectors.

6. Replace any cable ties cut at disassembly.

7. Perform the Case Front Assembly
Replacement procedure.

8. Perform the Case Cover Assembly
Replacement procedure.

TROUBLESHOOTING & REPAIR

F-45 F-45

MULTI-WELD 350

INPUT DIODE REMOVAL AND REPLACEMENT

WARNING

Service and repair should be performed by only Lincoln Electric factory trained personnel.
Unauthorized repairs performed on this equipment may result in danger to the technician
or machine operator and will invalidate your factory warranty . For your safety and to avoid
electrical shock, please observe all safety notes and precautions detailed throughout this
manual.

If for any reason you do not understand the test procedures or are unable to perform the
test/repairs safely, contact the Lincoln Electric Service Department for electrical trou­bleshooting assistance before you proceed. Call 1-800-833-9353 (WELD).

DESCRIPTION

The following procedure will aid the technician in removing and replacing stud type diodes
on the aluminum heat sinks of the Multi-Weld 350.

MATERIALS NEEDED

3/8" Nut driver, wrench or socket wrench
1/2" socket wrench and extension
17 mm Wrench or socket wrench
1

1

⁄4 " Open end wrench

Penetrox A13 joint compound
Loctite 271
“Slip” type torque wrench
No. 000 fine steel wool
Diagonal cutters
Wiring Diagram

This procedure should take approximately 45 minutes to perform.

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TROUBLESHOOTING & REPAIR

F-46 F-46

MULTI-WELD 350

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FIGURE F.11 – INPUT DIODE ASSEMBLY DETAILS

INPUT DIODE REMOVAL AND REPLACEMENT (CONTINUED)

REMOVAL PROCEDURE

Refer to Figure F.11.

1. Set the CC/CV power switch to OFF.

2. Remove input power to the machine.

ELECTRIC SHOCK can kill.

Disconnect input power before removing the
case cover and performing tests or making
repairs to the machine.

3. Perform the Case Cover Assembly
Removal procedure.

4. Perform the Power Capacitor Discharge
procedure.

5. Perform the Case Front Assembly
Removal procedure.

6. Perform the Input Contactor Removal
procedure.

7. Using the 3/8" socket wrench, remove the
bolt, nylon insulators and mylar insulation
sheet where the diode heat sink attaches to
the choke. Note order for replacement.

8. Using the 1/2" socket wrench and exten­sion, remove the nut, lock washer, flat
washer, and bolt holding the heat sink to the
input terminal strap. Note the flat washer
under the bolt head.

9. Using the 1/2" wrench, remove the bolt and
washers connecting the diode pig-tails to
the contactor strap if this was not done dur­ing input contactor removal.

WARNING

CONTACTOR
STRAP

PIGTAILS

HEAT
SINK

MYLAR

THERMOSTAT
(LEADS #306 ij)

CHOKE
ATTACHMENT
POINT

CHOKE

DIODE

MYLAR

INPUT

{

TERMINAL
STRAP
BOLT

}

TROUBLESHOOTING & REPAIR

F-47 F-47

MULTI-WELD 350

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INPUT DIODE REMOVAL AND REPLACEMENT (CONTINUED)

10. Disconnect thermostat leads #306 and
#307.

1 1. Carefully remove the input diode assembly.

12. Using the 1

1

⁄4" wrench, loosen the appropri-

ate diode and remove the diode that is to
be replaced.

13. Clean the area on the heat sink around the
diode mounting surface using a putty knife
or similar tool. DO NOT SCRATCH THE
DIODE MOUNTING SURFACE.

14. Polish the heat sink’s mounting surface to
provide a bright, clean surface where the
diode seats on the heat sink. Wipe the sur­face clean with a lint-free cloth or paper
towel.

15. Inspect the mounting surfaces of each new
diode. Remove all burrs and wipe clean.
Do not use steel wool or any abrasive
cleanser on the diode mounting surface.

16. Apply a thin (0.003" to 0.007") uniform
layer of Penetrox A13 joint compound to
the heat sink mounting surface.

17. Do not apply compound to the diode stud
or mounting threads.

18. Apply two drops of Loctite 271 to the diode
stud threads before tightening.

NOTE: The diode threads must be clean and
free of defects so that it can be finger tightened
before applying torque. A “slip” type torque
wrench must be used to tighten the diode.

19. Tighten the diode to the specifications in
the following table.

DIODE

STUD FOOT-POUNDS INCH-POUNDS

SIZE

3/4 - 16 25-27 300-324

REPLACEMENT PROCEDURE

Refer to Figure F.11.

1. Set the input diode assembly into the
machine base. Connect the heat sink to the
input terminal strap with the 1/2" bolt, wash­ers, and nut. Note order – see removal pro­cedures.

2. Install the heat sink to the choke, using the
3/8" bolt and nylon insulators, along with
the mylar insulation sheet. The mylar sheet
fits between the nylon insulators.

3. Connect thermostat leads #306 and #307.
See the Wiring Diagram.

4. Perform the Input Contactor Replace-
ment procedure. Be sure to connect the
input diode pig-tails to the contactor strap at
the contactor rear terminal.

5. Replace any cable ties cut at disassembly.

6. Perform the Case Front Assembly
Replacement procedure.

7. Perform the Case Cover Assembly
Replacement procedure.

TROUBLESHOOTING & REPAIR

F-48 F-48

MULTI-WELD 350

FAN MOTOR ASSEMBLY REMOVAL AND REPLACEMENT

WARNING

Service and repair should be performed by only Lincoln Electric factory trained personnel.
Unauthorized repairs performed on this equipment may result in danger to the technician
or machine operator and will invalidate your factory warranty . For your safety and to avoid
electrical shock, please observe all safety notes and precautions detailed throughout this
manual.

If for any reason you do not understand the test procedures or are unable to perform the
test/repairs safely, contact the Lincoln Electric Service Department for electrical trou­bleshooting assistance before you proceed. Call 1-800-833-9353 (WELD).

DESCRIPTION

The following procedure will aid the technician in removing and replacing the cooling fan
and motor of the Multi-Weld 350.

MATERIALS NEEDED

3/8" Nut driver, wrench or socket wrench
17 mm socket wrench and extension
Phillips head screw driver
Diagonal cutters

This procedure should take approximately 45 minutes to perform.

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TROUBLESHOOTING & REPAIR

F-49 F-49

MULTI-WELD 350

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FIGURE F.12 – FAN MOTOR ASSEMBLY DETAILS

FAN MOTOR ASSEMBLY REMOVAL AND REPLACEMENT(CONTINUED)

REMOVAL PROCEDURE

Refer to Figure F.12.

1. Set the CC/CV power switch to OFF.

2. Remove input power to the machine.

ELECTRIC SHOCK can kill.

Disconnect input power before removing the
case cover and performing tests or making
repairs to the machine.

WARNING

MOTOR
LEADS
#303A
#330

FAN
MOTOR

SCREWS (2)

TROUBLESHOOTING & REPAIR

F-50 F-50

MULTI-WELD 350

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FAN MOTOR ASSEMBLY REMOVAL AND REPLACEMENT(CONTINUED)

3. Perform the Input Diode Removal proce­dure.

4. Disconnect the red motor lead from leads
#303 and #303A and the blue motor lead
from lead #300 at their in-line connectors.
Cut any necessary cable ties.

5. Disconnect the two plug harness connec­tions at the top of the tunnel assembly.

6. Using the phillips head screw driver,
remove the two screws holding the fan
motor housing to the tunnel assembly.

7. Carefully remove the fan motor assembly.

REPLACEMENT PROCEDURE

1. Set the fan motor assembly into the
machine, against the tunnel assembly, with
the motor nameplate label facing into the
tunnel assembly.

2. Connect the red motor lead to leads #303
and #303A and the blue motor lead to lead
#300 at their in-line connectors.

3. Mount the fan motor housing to the tunnel
assembly with two phillips screws.

4. Connect the two plug harness connections
at the top of the tunnel assembly.

5. Replace any cable ties previously removed.

6. Perform the Input Diode Replacement
procedure.

TROUBLESHOOTING & REPAIR

F-51 F-51

MULTI-WELD 350

POWER CAPACITOR REMOVAL AND REPLACEMENT

WARNING

Service and repair should be performed by only Lincoln Electric factory trained personnel.
Unauthorized repairs performed on this equipment may result in danger to the technician
or machine operator and will invalidate your factory warranty . For your safety and to avoid
electrical shock, please observe all safety notes and precautions detailed throughout this
manual.

If for any reason you do not understand the test procedures or are unable to perform the
test/repairs safely, contact the Lincoln Electric Service Department for electrical trou­bleshooting assistance before you proceed. Call 1-800-833-9353 (WELD).

DESCRIPTION

This procedure will aid the technician in the removal and replacement of the power capac­itors on the Multi-Weld 350.

MATERIALS NEEDED

3/8" Wrench or socket wrench
Slot head screw driver
7/16" Wrench
Resistor (25 – 1000 ohms, 25 watts minimum)
Wiring Diagram

This procedure should take approximately 30 minutes to perform.

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TROUBLESHOOTING & REPAIR

F-52 F-52

MULTI-WELD 350

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FIGURE F.13 – POWER CAPACITOR MOUNTING DETAILS

POWER CAPACITOR REMOVAL AND REPLACEMENT (CONTINUED)

PROCEDURE

Refer to Figure F.13.

1. Set the CC/CV power switch to OFF.

2. Remove input power to the machine.

ELECTRIC SHOCK can kill.

Disconnect input power before removing the
case cover and performing tests or making
repairs to the machine.

3. Perform the Case Cover Assembly
Removal procedure.

4. Perform the Power Capacitor Discharge
procedure.

5. Disconnect the two plug harness connec­tions at the top of the tunnel assembly.

6. Disconnect the plug harness connection
above each Chopper PC board.

WARNING

CLAMP

BRACKET

ANALOG CONTROL
SUPPLY PC BOARD
(4 SCREWS)

SCREWS (2)

CHOPPER
PC BOARD

+

-

RIGHT
SIDE

CAPACITOR
POSITIVE
STRAP

CAPACITOR
NEGATIVE
STRAP
LEADS

#X4A
#X1A

#X4
#X1
#401
#401A

LEFT
SIDE

TROUBLESHOOTING & REPAIR

F-53 F-53

MULTI-WELD 350

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POWER CAPACITOR REMOVAL AND REPLACEMENT (CONTINUED)

7. Using the slot head screw driver, remove
the two screws and lock washers from the
tunnel assembly top cover. Then remove
the four screws, lock washers, and flat
washers that mount the Analog Control
Power Supply PC Board. This will allow
you to access the clamps that hold the
capacitors to their brackets in the heat
sinks.

8. Lift off the top cover of the tunnel assem­bly. Peel away the adhesive-backed rub­ber stripping (if present) as necessary.
Use care – the stripping may tear.

9. Using the slot head screw driver, loosen
the clamp from around the bracket of the
capacitor you want to remove.

10. Using the 7/16" wrench, remove heavy
leads #X1, #X4 and small leads #401 and
401A (left side) or #X1A and #X4A (right
side) of the capacitor terminals. Note the
fasteners for reassembly: bolt, lock wash­er, and flat washer. See the Wiring
Diagram.

11. Using the 7/16" wrench, remove the two
bolts holding the negative strap to the
diode module. Note the fasteners for
reassembly: bolt, lock washer, two flat
washers.

12. Using the 7/16" wrench, remove the two
nuts holding the positive strap to the
Chopper PC board. Hold the bolt head
behind the board to remove each nut.
Note the fasteners for reassembly: flat
washer, lock washer, nut. Note the place­ment of the reverse diode lead on the bot­tom bolt.

13. Push the capacitor from the inside, out of
the heat sink. Note that the bracket stays
in the heat sink.

REASSEMBLY

1. Slide the capacitor into the heat sink.

Position the positive (+) terminal next to
the Chopper PC board.

2. Tighten the bracket clamp.

3. Replace the leads and straps as labeled
(Figure F.13) and tighten the fasteners.
Use the 7/16" socket and torque wrench to
tighten the capacitor terminal bolt to 50-60
in-lbs. Tighten the nuts holding the positive
strap to the Chopper PC board to 50-60 in­lbs.

4. Tighten the two 7/16" screws that hold the
negative strap to the diode module to 30-40
in-lbs.

5. Replace any adhesive-backed rubber strip­ping, if present, that was damaged during
disassembly.

6. Replace the Analog Control Power Supply
PC Board.

7. Replace the tunnel assembly top cover.

8. Connect the wire harness plug assemblies
above each Chopper PC Board and above
the tunnel assembly (four plugs total).

9. Perform the Case Cover Assembly
Replacement procedure.

TROUBLESHOOTING & REPAIR

F-54 F-54

MULTI-WELD 350

CHOPPER PC BOARD AND DIODE MODULE

REMOVAL AND REPLACEMENT

WARNING

Service and repair should be performed by only Lincoln Electric factory trained personnel.
Unauthorized repairs performed on this equipment may result in danger to the technician
or machine operator and will invalidate your factory warranty . For your safety and to avoid
electrical shock, please observe all safety notes and precautions detailed throughout this
manual.

If for any reason you do not understand the test procedures or are unable to perform the
test/repairs safely, contact the Lincoln Electric Service Department for electrical trou­bleshooting assistance before you proceed. Call 1-800-833-9353 (WELD).

DESCRIPTION

This procedure will aid the technician in the removal and replacement of the Chopper PC
Board and the diode module assembly.

MATERIALS NEEDED

3/8" Wrench or socket wrench
7/16" Wrench or socket wrench
1/2" Wrench
3/16" Allen head wrench
9/64" Allen head wrench
Torque wrench with 7/16" hex and 1/4" and 9/64" allen head sockets
Phillips head screw driver
Diagonal cutters
Electrical thermal joint compound – Penetrox A-13
Resistor (25 – 1000 ohms, 25 watts minimum)
Small block of wood (approximately 1" x 3")

This procedure should take approximately 1 hour to perform.

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TROUBLESHOOTING & REPAIR

F-55 F-55

MULTI-WELD 350

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FIGURE F. 14 – CHOPPER PC BOARD AND DIODE MODULE CONNECTIONS

CHOPPER PC BOARD REMOVAL AND REPLACEMENT (CONTINUED)

REMOVAL

Refer to Figure F.14.

1. Set the CC/CV power switch to OFF.

2. Remove input power to the machine.

ELECTRIC SHOCK can kill.

Disconnect input power before removing the
case cover and performing tests or making
repairs to the machine.

WARNING

ALLEN-HEAD
SCREWS (2)

CHOPPER
PC BOARD

CAPACITOR
POSITIVE

+

-

STRAP

REVERSE
DIODE LEAD
CONNECTION

HEX-HEAD
BOLTS (2)

AMPS

A

V

MULTI-WELD 350

ELECTRODE

WORK

VOLTS

INPUT

LINCOLN

ELECTRIC

CHOPPER TECHNOLO GY

4 SCREWS
ACCESSED
FROM BOTTOM

TROUBLESHOOTING & REPAIR

F-56 F-56

MULTI-WELD 350

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CHOPPER PC BOARD REMOVAL AND REPLACEMENT (CONTINUED)

3. Perform the Case Cover Removal proce-
dure.

4. Perform the Power Capacitor Discharge
procedure.

5. Carefully turn the machine onto its side.

6. Using the 3/8" wrench, remove the four
screws holding the tunnel assembly to the
machine base. Support the tunnel assem­bly, then carefully turn the machine back
upright.

7. With the slot head screw driver, carefully
raise the tunnel assembly unit about one
inch and block it with the piece of wood.
This will allow access to the bottom allen
head screws on the Chopper PC Board.
Peel away the adhesive-backed rubber
stripping if present. Use care – the strip­ping may tear.

8. Disconnect the plug harness connection
above the Chopper PC Board. Slip the
wires out of the cord clip.

9. Using the 7/16" wrench, loosen the bolt at
the positive capacitor terminal. Then
remove the two nuts, lock washers and flat
washers holding the positive strap to the
Chopper PC Board. Hold the screw heads
behind the board with your finger to
remove the nuts. Note the placement of
the reverse diode lead on the bottom bolt.
Note the fastener order for reassembly: flat
washer, lock washer, nut.

10. With the 7/16" wrench, remove the two
hex-head bolts, lock washers, and flat
washers holding the Chopper PC Board to
the heat sink. Catch the copper stand-offs
behind the board.

1 1. Using the 3/16" allen head wrench, remove

the two allen-head screws and lock wash­ers holding the Chopper PC Board to the
heat sink.

12. Swing the positive capacitor strap out of
the way and remove the Chopper PC
Board.

REPLACEMENT

Refer to Figure F.14.

1. Make sure the mating surfaces between the
copper and the heat sink are clean, dry , and
free of grease.

2. Apply a thin coating of electrical thermal
joint compound (Penetrox A-13) to the mat­ing surfaces between the copper and the
aluminum heat sink.

3. Using the torque wrench and 3/16" allen
head socket, install the two allen-head
screws and lock washers that hold the
Chopper PC Board to the heat sink.
Tighten the screws finger tight, then to
between 24 and 28 in-lbs., then again to
between 40 and 48 in-lbs.

4. Using the 7/16" socket and torque wrench,
install the two bolts, lock washers, and flat
washers that hold the Chopper PC Board to
the heat sink. Note the two spacers
required. Tighten the bolts finger tight, then
to between 50 and 60 in-lbs.

5. Put the positive strap (+) in position and the
proper heavy lead. Using the 7/16" wrench,
tighten the bolt at the positive capacitor ter­minal to between 50 and 60 in-lbs. Then
put the flat washers, lock washers and nuts
on the board side of the strap with the
reverse diode lead on the bottom connec­tion. Tighten to between 50 and 60 in-lbs.

6. Remove the wooden blocking and carefully
lower the tunnel assembly onto the
machine base. Support the tunnel assem­bly and turn the machine onto its side.

7. With the 3/8" wrench, install the four screws
that hold the tunnel assembly to the
machine base. Turn the machine back
upright.

8. Connect the harness plug above the
Chopper PC board. Slip the wires into the
cord clip.

See the procedures following for removal and
replacement of the diode module. When proce­dures are complete, perform the Case Cover
Assembly Replacement procedure.

TROUBLESHOOTING & REPAIR

F-57 F-57

MULTI-WELD 350

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FIGURE F.15 – DIODE MODULE MOUNTING DETAILS

DIODE MODULE REMOVAL AND REPLACEMENT

REMOVAL

Refer to Figure F.15.

1. Set the CC/CV power switch to OFF.

2. Remove input power to the machine.

ELECTRIC SHOCK can kill.

Disconnect input power before removing the
case cover and performing tests or making
repairs to the machine.

WARNING

+

-

3/16"
ALLEN-HEAD
SCREWS (2)

AMPS

A

V

MULTI-WELD 350

E

W

O

R

K

VOLTS

L

E

C

T

R

O

D

E

IN

LINCOLN

P

ELECTRIC

U

T

CHOPPER TECHNOLOGY

DIODE
MODULE

CAPACITOR
NEGATIVE
STRAP

9/64"
ALLEN-HEAD

MOUNTING
BOLTS (2)

SCREW (1)

TROUBLESHOOTING & REPAIR

F-58 F-58

MULTI-WELD 350

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DIODE MODULE REMOVAL AND REPLACEMENT(CONTINUED)

3. Perform the Case Cover Removal proce-
dure.

4. Perform the Power Capacitor Discharge
procedure.

5. Carefully turn the machine onto its side.

6. Using the 3/8" wrench, remove the four
screws holding the tunnel assembly to the
machine base. Then carefully turn the
machine back upright.

7. With the slot head screw driver, carefully
raise the tunnel assembly unit about one
inch and block it with the piece of wood.
This will allow access to the bottom allen
head screw on the diode module. Peel
away the adhesive-backed rubber stripping
as necessary. Use care – the stripping
may tear.

8. Using the 7/16" wrench, remove the two
outer screws, lock washers, and flat wash­ers holding the negative capacitor strap to
the diode module. Note fastener order for
reassembly.

9. Using the 3/16" allen head wrench, remove
the two screws, flat washers, and spring
washers holding the diode module to the
heat sink.

10. Using the 9/64" allen wrench, remove the
set screw from the center of the diode
module.

11. Remove the diode module from the heat
sink.

REPLACEMENT

Refer to Figure F.15.

The proper tightening sequence is required to
mount the diode module to the heat sink in
order to avoid warping the base plate. Apply
the proper torque to all fasteners.

1. Be sure the heat sink mounting surface is
clean, dry, and free of grease.

2. Apply a thin, even coat (.1 to .25mm or .004
to .010 in) of Penetrox A13 thermal joint
compound to the diode module base plate
only, under the plastic body of the module.
Do not apply compound to the area under
the mounting holes.

3. Press the module firmly against the heat
sink, aligning the mounting holes.

CAUTION

TROUBLESHOOTING & REPAIR

F-59 F-59

MULTI-WELD 350

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FIGURE F.16 – DIODE MODULE TIGHTENING SEQUENCE

DIODE MODULE REMOVAL AND REPLACEMENT(CONTINUED)

Refer to Figure F.16.

4. Place a spring washer then a flat washer
over each outer mounting screw and insert
them into the holes. Insert the allen head
screw into the center hole. Tighten all three
screws 2 – 3 turns each, finger-tight only.
(1)

5. Using the torque wrench and 7/16" socket,
tighten the outer screws to between 5.0 and
10 in-lbs. (2)

6. Using the torque wrench and 9/64" allen
head socket, tighten the center screw
between 12 and 18 in-lbs. (3)

7. Now tighten the two outer screws between
30 and 40 in-lbs. (4)

8. Place the negative capacitor strap over the
diode module and align the mounting holes.
Place a lock washer and two flat washers

over each 7/16" screw and insert them into
the holes. Using the torque wrench and
7/16" socket, tighten each screw between
30 and 40 in-lbs.

9. Install the 7/16" bolt, lock washer, flat
washer, heavy lead and negative strap to
the negative terminal on the capacitor.
Tighten the bolt to 50-60 in-lbs.

10. Remove the wooden blocking and careful­ly lower the tunnel assembly onto the
machine base. Support the tunnel assem­bly and turn the machine onto its side.

11. With the 3/8" wrench, install the four
screws that hold the tunnel assembly to the
machine base. Turn the machine back
upright.

12. Perform the Case Cover Assembly
Replacement procedure.

1

SPRING WASHER

PLAIN WASHER

3

12-18 IN-LBS.

2 TO 3

TURNS EACH

2

5.0-10 IN-LBS.

FINGER TIGHT

5.0-10 IN-LBS.

4

30-40 IN-LBS.

TROUBLESHOOTING & REPAIR

F-60 F-60

MULTI-WELD 350

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RETEST AFTER REPAIR

Retest a machine:

• If it is rejected under test for any reason that requires you to remove any mechanical part which could affect the
machine’s electrical characteristics. OR

• If you repair or replace any electrical components.

IDLE AMPS

Input Volts Maximum Idle Amps

50 – 113 VDC 1 Amp

OPEN CIRCUIT VOLTAGES

Mode Input Voltage Open Circuit Voltage

CC Stick 72 – 113 VDC 74 – 78 VDC
CC Stick 60 – 72 VDC Volts In + 4 VDC

CC Pipe (200 Apreset) 72 – 113 VDC 73 – 78 VDC

CV Min. Preset 60 – 113 VDC 17 – 20 VDC

CV Max. Preset 60 – 113 VDC 50 – 54 VDC

LOAD TEST

Mode Input Voltage Output Amps and Volts

CC Stick/Gouge 60 – 113 VDC 100 Amps @ 24 VDC
CC Stick/Gouge 60 – 113 VDC 200 Amps @ 28 VDC
CC Stick/Gouge 60 – 113 VDC 350 Amps @ 34 VDC

FAN AS NEEDED (F.A.N.)

The fan should turn on when the machine is loaded and stay on for 50–70 seconds after the output load is
removed.