Lincoln Electric SVM129-B User Manual

SVM129-B

OCTOBER, 2006

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 CON­TAINED THROUGHOUT. And,

most importantly, think before
you act and be careful.

For use with machine code numbers:10151,10152,10153,10309,10381,10382,10383,11090,11091,11092,

11115,11116

INVERTEC

®

STT

TM

& STT II

TM

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SERVICE MANUAL

• 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 © 2006 Lincoln Global Inc.

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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 weld­ing 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.

i

SAFETY

i

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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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. The operation of welding fume control equipment is affected
by various factors including proper use and positioning of the
equipment, maintenance of the equipment and the specific
welding procedure and application involved. Worker expo­sure level should be checked upon installation and periodi­cally thereafter to be certain it is within applicable OSHA PEL
and ACGIH TLV limits.

5.c.

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.d. 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.e. 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.f. Also see item 1.b.

AUG 06

ii

SAFETY

ii

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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.

iii

SAFETY

iii

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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 soud

e 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

iv

SAFETY

iv

MASTER TABLE OF CONTENTS FOR ALL SECTIONS

v v

INVERTEC STT

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

STT Parts .......................................................................................................................................P257

STT II Parts....................................................................................................................................P294

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TABLE OF CONTENTS

- INSTALLATION SECTION -

Section A-1 Section A-1

INVERTEC STT

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

Technical Specifications (Codes 11092 & Below) .......................................................................A-2

Technical Specifications (Codes 11115 & 11116) ........................................................................A-3

Location.......................................................................................................................................A-4

Stacking.......................................................................................................................................A-4

Tilting...........................................................................................................................................A-4

Machine Grounding and High Frequency Interference Protection..............................................A-4

Input Connections .......................................................................................................................A-4

Supply Connections..............................................................................................................A-4

Input Cable Installation and Connection...............................................................................A-5

Ground Connection...............................................................................................................A-5

Input Voltage Reconnect Procedure ...........................................................................................A-6

Output Connections ....................................................................................................................A-6

Wire Feeder Output Connections .........................................................................................A-6

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INSTALLATION

A-2 A-2

INVERTEC STT

STANDARD VOLTAGE INPUT CURRENT AT RATED OUTPUT

208/230/460/3/60 HZ 32/30/16

200/220/380/415/440/3/50/60 HZ 33/30/18/17/16

TECHNICAL SPECIFICATIONS –Invertec STT & STT II (For Codes 11092 and BELOW)

INPUT- THREE PHASE ONLY

RATED OUTPUT

RECOMMENDED INPUT WIRE AND FUSE SIZES

INPUT VOLTAGE FUSE(SUPER LAG) INPUT AMPERE TYPE 75 C TYPE 75 C

AND FREQUENCY OR BREAKER RATING ON COPPER COPPER

SIZE NAMEPLATE SUPPLY WIRE GROUND WIRE

IN CONDUIT IN CONDUIT

AWG (IEC) SIZES AWG (IEC) SIZES

208/60 40 32
230/60 40 30
460/60 30 16
200/50/60 40 33

220/50/60 40 30 10 (6 mm2) 10 (6 mm2)
380/50/60 30 18
415/50/60 30 17
440/50/60 30 16

HEIGHT WIDTH DEPTH WEIGHT

23.2 in 13.2 in. 24.4 in. 100 lbs.

589 mm 336 mm 620 mm 46 kg

OUTPUT

DUTY CYCLE AMPS VOLTS AT RATED AMPS

60% Duty Cycle 225 29

100% Duty Cycle 200 28

CURRENT RANGE OPEN CIRCUIT VOLTAGE AUXILIARY POWER

Peak Current

1

0 - 450 Amps 85 VDC Maximum 115 2VAC @ 4 Amps

Background 0 - 125 Amps 42 VAC @ 4 Amps

1

At low input voltages (below 208 VAC) and input voltages of 380 VAC through 415 VAC there may be a 15% reduction in Peak Current.

2

115 VAC not present on European Models.

PHYSICAL DIMENSIONS

INSTALLATION

A-3 A-3

INVERTEC STT

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STANDARD VOLTAGE INPUT CURRENT AT RATED OUTPUT

200/208/3/50/60 HZ 36/34

200/208/380/400/415/3/50/60 HZ 36/34/20/19/18

TECHNICAL SPECIFICATIONS –Invertec STT II (For Codes 11115 AND 11116)

INPUT- THREE PHASE ONLY

RATED OUTPUT

RECOMMENDED INPUT WIRE AND FUSE SIZES

INPUT VOLTAGE FUSE(SUPER LAG) INPUT AMPERE TYPE 75 C TYPE 75 C

AND FREQUENCY OR BREAKER RATING ON COPPER COPPER

SIZE NAMEPLATE SUPPLY WIRE GROUND WIRE

IN CONDUIT IN CONDUIT

AWG (IEC) SIZES AWG (IEC) SIZES

200/50/60 40 36
208/50/60 40 34

380/50/60 30 20 10 (6 mm2) 10 (6 mm2)
400/50/60 30 19
415/50/60 30 18

HEIGHT WIDTH DEPTH WEIGHT

23.2 in 13.2 in. 24.4 in. 100 lbs.

589 mm 336 mm 620 mm 46 kg

OUTPUT

DUTY CYCLE AMPS VOLTS AT RATED AMPS

60% Duty Cycle 225 29

100% Duty Cycle 200 28

CURRENT RANGE OPEN CIRCUIT VOLTAGE AUXILIARY POWER

Peak Current 0 - 450 Amps 88 VDC Maximum 115

1

VAC @ 4 Amps

Background 0 - 125 Amps 42 VAC @ 4 Amps

1

115 VAC not present on European Models.

PHYSICAL DIMENSIONS

INSTALLATION

A-4 A-4

INVERTEC STT

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ELECTRIC SHOCK can kill.

• Only qualified personnel should
perform this installation.

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

•Turn the power switch on the Invertec
STT “OFF” before connecting or discon­necting input power lines, output cables,
or control cables.

• Do not touch electrically hot
parts.

• Always connect the ground terminal to a
good electrical earth ground.

WARNING

MACHINE GROUNDING AND HIGH
FREQUENCY INTERFERENCE
PROTECTION

The machine may not be suitable for use in an envi­ronment where high frequency is present. For exam­ple do not place the machine in close proximity to “TIG”
or “PLASMA” operations. To minimize high frequency
interference:

Locate the STT II power source more than 15
feet (4.5 m) away from high frequency units
and more than 25 feet (7.6 m) separation
between ground connections or welding arcs
of high frequency units.

Provide proper electrical ground to the
machine per local and national electrical
codes.

INPUT CONNECTIONS

FAILURE TO FOLLOW THESE INSTRUCTIONS
CAN CAUSE IMMEDIATE FAILURE OF COMPO­NENTS WITHIN THE WELDER.

Turn the input power off at the disconnect switch
before attempting to connect the input power lines.

Connect the green lead of the power cord to ground
per local and national electrical codes.

SUPPLY CONNECTIONS

Be sure the voltage, phase, and frequency of the input
supply is as specified on the rating plate. Input Power
supply line entry in provided on the case back of the
machine. See figure A.1 for location of the rating plate.

The Invertec STT II should be connected only by a
qualified electrician. Installation should be made in
accordance with local and national codes. Refer to the
“Technical Specifications” at the beginning of this
section for proper fuse sizes, ground wire, and input
supply power cable sizes.

Some models come from the factory with an input
power cord. If your model does not include the input
power cord install the proper size input cable and
ground cable according to “INPUT CABLE INSTAL-

LATION AND CONNECTION”.

SELECT SUITABLE LOCATION

Locate the machine where there is free circulation of
clean air. Place the machine so that air can freely cir­culate into the sides and out of the rear of the
machine. Dirt and dust that can be drawn into the
machine should be kept to a minimum. Failure to
observe these precautions can result in excessive
operating temperatures and nuisance shut down of the
Invertec STT II.

This machine carries an enclosure rating of IP21S. It
should not be placed in extremely damp or dirty loca­tions. It should not be exposed to rain or snow.

STACKING

The Invertec STT II cannot be stacked.

TILTING

Place the machine on a secure, level surface otherwise
the unit may topple over.

Read and understand entire Installation
Section before starting installation.

INSTALLATION

A-5 A-5

INVERTEC STT

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INPUT CABLE INSTALLATION AND CON­NECTION

A cable strain relief is provided at the supply line entry
and is designed to accommodate cable diameters of
.310 - 1.070 in. (7.9 - 27.2 mm). On European models
the strain relief is designed to accommodate cable
diameters of .709 - 1.000 in. (18.0 - 25.4 mm). Refer to
“Technical Specifications” at the beginning of this sec­tion for the proper input cable sizes. Refer to Figure A.1
and perform the following steps:

1. Remove the wraparound cover of the
Invertec STT II.

2. Feed the input cable through the input cable
entry access hole at the right rear of the
machine.

3. Route the cable through the cable hangers,
located along the lower right inside edge of
the machine, up to the power switch located on
the front panel.

4. Strip away 102 mm (4 in.) of the outer jacket.
Trim fillers and strip conductor jackets to
connect to the power switch.

5. Connect the three phase line con­ductors to the power switch termi­nals labeled U, V and W. Tighten
the connections to 3.0 Nm. (27 in.-lb.) torque.

6. Securely tighten the cable strain relief located

on the case back of the machine.

GROUND CONNECTION

1. Connect the ground terminal to earth
ground per National Electrical Code.

2. Replace the wraparound cover of the

Invertec STT II.

CASE BACK

RATING PLATE

INPUT CABLE
ENTRY ACCESS
& CABLE STRAIN RELIEF

FIGURE A.1 CASE BACK

A-6

INSTALLATION

A-6

INVERTEC STT II

FIGURE A.2 RECONNECT PANEL

I

NPUT VOLTAGE RECONNECT

PROCEDURE

As shipped from the factory, multiple voltage machines
are internally configured for the highest input voltage
(440-460 VAC), for Codes 11092 and below and (380­415 VAC), for Codes 11115 and 11116.

1. For Connections to 440 or 460 VAC verify

the inter­nal configurations to the procedures shown below and
refer to Figure A.2.

2. For Connections to 200,208,220,230,380,400 or 415
VAC follow the procedure shown below and refer to fig­ure A.2.

NOTE: Turn main power to the machine OFF

before performing the reconnect procedure.
Failure to do so will result in damage to the
machine. DO NOT switch the reconnect bar with
machine power ON.

------------------------------------------------------------------------

To Operate at Procedure

460 or 440 VAC 1. Open reconnect panel
(Codes 11092 and access door on wrap­around.
below) 2. Move input voltage switch

to Voltage = 380 -460V pos­ition.

3. Move lead “A” to 440-460
Terminal.

380 or 415 VAC 1. Open reconnect panel
(Codes 11092 and access door on wrap­around.
below)

2. Move input voltage switch
to Voltage = 380-460V
position.

3. Move lead “A” to 380-415
Terminal.

380,400 or 415 VAC 1. Open reconnect panel
(Codes 11115 and access door on wrap­around.

11116) 2. Move input voltage switch

to Voltage = 380-460V
position.

3. Move lead “A” to 380-415
Terminal.

220 or 230 VAC 1. Open reconnect panel
(Codes 11092 and access door on wrap­around.
below) 2. Move input voltage switch

to Voltage = 200 -230V
position.

3. Move lead “A” to 220-230
Terminal.

200 or 208 VAC 1. Open reconnect panel
(Codes 11092 and access door on wrap­around.
below) 2. Move input voltage switch

to Voltage = 200 -230V
position.

3. Move lead “A” to 200-208
Terminal.

200 or 208 VAC 1. Open reconnect panel
(Codes 11115 and access door on wrap-around.

11116) 2. Move input voltage switch
to Voltage = 200 -230V
position.

3. Move lead “A” to 200-208
Terminal.

OUTPUT CONNECTIONS

WIRE FEEDER OUTPUT CONNECTIONS

Refer to the Accessories section of this manual for
instructions on connecting a wire feeder to the Invertec
STT II.

The LN-742 or STT-10 wire feeder is the recommend­ed feeder for use with the Invertec STT II.

WARNING

4A

380-415
OR

OR
200-208

*

*

*

(NOT PRESENT ON ALL MODELS)

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Section B-1 Section B-1

INVERTEC STT

TABLE OF CONTENTS

- OPERATION SECTION -

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

Safety Precautions ......................................................................................................................B-2

General Description ....................................................................................................................B-3

Recommended Equipment..........................................................................................................B-3

Operating Controls ......................................................................................................................B-3

Design Features..........................................................................................................................B-3

Welding Capability ......................................................................................................................B-3

Limitations ...................................................................................................................................B-3

Operational Features and Controls.............................................................................................B-4

Welding Operation ......................................................................................................................B-5

Welding Parameters and Guidelines ..........................................................................................B-6

Recommended Settings for STT II..............................................................................................B-7

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B-2 B-2

INVERTEC STT

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.

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.

OPERATING INSTRUCTIONS

Read and understand entire section before
operating machine.

GENERAL WARNINGS

SAFETY PRECAUTIONS

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

WARNING

OPERATION

OPERATION

B-3 B-3

INVERTEC STT

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GENERAL DESCRIPTION

The Invertec STT II is a 225-ampere inverter based arc
welding power source specifically designed for the STT
welding process. It is neither a constant current (CC)
nor a constant voltage (CV) machine. It is a power
source that delivers current of a desired wave form and
characteristics that are superior to conventional short
circuiting GMAW. The process is optimized for short­circuiting GMAW welding.

RECOMMENDED EQUIPMENT

The LN-742 or STT-10 wire feeder is recommended for
use with the STT II. The LN-7 GMA, LN-9 GMA, NA-5,
and NA-5R can all be used with the STT II. However,
these units can only be used to feed wire since these
feeders have no provision for control of the STT output.

OPERATING CONTROLS

The Invertec STT II has the following controls as stan­dard: On/Off switch, Peak Current adjustment,
Background Current adjustment, Hot Start adjustment,
Tailout, and 2 toggle switches; one for wire size selec­tion and one for wire type selection.

DESIGN FEATURES AND ADVANTAGES

• State of the art inverter technology yields high power

efficiency, excellent welding performance, light­weight and compact design.

• Twist-Mate™ output terminals.

• Digital meters for procedure settings are standard.

• Automatic Inductance or Pinch Control.

• Solid state circuitry for extra long component life.

• Current feedback ensures that original procedure

settings all remain constant.

• Arc Sense lead assembly (Electrode and Work),

connects through a 4-pin case front connector.

• Peak Current and Background Current may be

remotely controlled.

• Thermostat and FET over current protector prevent

overheating from overloads, high ambient tempera­tures, or loss of air flow.

• High temperature Class H insulation.

• Protection circuits and ample safety margins prevent

damage to the solid state components from transient
voltages and high currents.

• Preset welding current capability.

• STT II offers improvements over the previous model.
Approximately 40% increase in deposition rate capa­bility, and a significant increase in travel speed.

WELDING CAPABILITY

The Invertec STT II is rated at 225 amps, 29 volts, at
60% duty cycle on a ten minute basis. It is capable of
higher duty cycles at lower output currents. If the duty
cycle(s) are exceeded, a thermal protector will shut off
the output until the machine cools to a reasonable
operating temperature.

LIMITATIONS

• May not be suitable for use in an environment with

High Frequency present. (“See Machine Grounding
and High Frequency Protection” in the Installation

section of this manual)

• Suitable for indoor use only (IEC IP21S).

OPERATION

B-4 B-4

INVERTEC STT

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1. POWER SWITCH: Turns output

power ON and OFF. This switch
also controls auxiliary power
available through the 14-pin Wire
Feeder Receptacle.

2A. BACKGROUND CURRENT OUTPUT CONTROL:

The output current is switched to the
Background level at the conclusion of the
preceding Peak Current pulse. This knob
allows preset adjustment of the amplitude
of the background current up to 125
amperes.

2B. BACKGROUND CURRENT DISPLAY METER:

This is a digital meter for displaying the
preset Background Current. This meter
displays in 1 amp increments. This meter
does not indicate the actual welding cur­rent, only the preset current.

3A. PEAK CURRENT OUTPUT CONTROL: The

beginning portion of the welding arc is a
pulse of current referred to as Peak
Current. This knob allows preset adjust­ment of the amplitude of the peak current
up to 450 amperes.

3B. PEAK CURRENT DISPLAY METER: This

is a digital meter for displaying the preset
Peak Current. This meter displays in 1
amp increments. This meter does not indi

­cate actual welding current only the preset
current.

4. HOT START CONTROL POTENTIOMETER:

“Hot Start” provides approximately 25% to
50% more current during the initial start of
the weld for improved arc starting and bead
appearance. This control adjusts the dura­tion of this “Hot Start” current. The control range is
from 0 to 10, where 0 corresponds to the zero or no
“Hot Start”, and 10 is maximum for a “Hot Start” last­ing for about four (4) seconds.

5. TAILOUT: Alters the current waveform to increase

deposit rate and travel speed. The Minimum setting
sets STT II to the original STT waveform. As tailout
is increased peak and Background current may
need to be reduced to maintain optimum perfor­mance.

OPERATIONAL FEATURES AND CONTROLS

All operator controls are located on the case front of the Invertec STT II. Refer to Figure B.1 for locations.

FIGURE B.1 CASE FRONT CONTROLS

4

1

2

3

7

6

8

10

9

11

14

15

12

13

5

ON

OFF

AAV

OPERATION

B-5 B-5

INVERTEC STT

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6. WIRE SIZE SELECT SWITCH: This toggle switch

selects between electrode diameters of .035” (1 mm)
and smaller or .045” (1.2 mm) and larger. The .035”
(1 mm) position provides improved performance of
smaller diameter wires at higher wire feed speeds.

7. WIRE TYPE SELECT SWITCH: This toggle switch

selects between mild or stainless steel. In the stain­less position, the pulse width of the Peak Current is
changed from 1 to 2 ms for better performance for
stainless steel welding.

8. THERMAL SHUT-DOWN INDICATOR: This light

will indicate that either the internal thermo­stat(s) or the FET over current sensor has
actuated. Machine output will return after
the internal components have returned to normal
operating temperature (if the thermostat(s)
“opened”) or after about 3-7 seconds (if the FET over
current sensor activated).

9.

REMOTE RECEPTACLE: This is a 10 pin MS-type
connector for remote control of Peak Current and
Background Current. Trigger switch connections
are also provided. The presence of the mating con­nector is automatically sensed, disabling the front panel Peak
and Background Current controls. Refer to “REMOTE CON­TROL CONNECTOR” in the ACCESSORIES Section of this
manual for more information.

10. WIRE FEEDER RECEPTACLE: This is 14

pin MS-type connector for the wire feeder
connection. 115 and 42 VAC along with
the trigger switch connections are provid­ed. (Only 42 VAC is available on European mod­els). There are no provisions for voltage control of
the power source by the wire feeder. Refer to the
Accessories section of this manual for wire feeder
connection instructions.

11. ARC SENSE RECEPTACLE:

This is a four pin MS­type connector for WORK and ELECTRODE sense
leads. The STT requires a WORK sense and ELEC­TRODE sense lead for proper operation. The
ELECTRODE sense lead is bolted together with
power source electrode lead at the wire feeder gun
block. The WORK sense lead is furnished with an
“alligator” type clip for connection to the work piece.
Refer to the LN 742 or STT-10 wire feeder connec­tion instructions in the Accessories section of this
manual for proper connection of these leads.

12. 42V AUXILIARY POWER CIRCUIT BREAKER:

The 42 VAC supply is protected from excessive current
draws with a 6 amp circuit breaker. When the
breaker “trips” its button will extend.
Depressing this button will reset the breaker.

13. 115V AUXILIARY POWER CIRCUIT BREAKER
(Not on European Models): The 115 VAC
supply is protected from excessive current
draws with a 6 amp circuit breaker. When
the breaker “trips” its button will extend.
Depressing this button will reset the breaker.

14. WORK TERMINAL: This twist-mate con-
nection is the negative output terminal for
connecting a work cable and clamp to the
workpiece.

15. ELECTRODE TERMINAL: This twist-mate
connection is the positive output terminal
for connecting an electrode cable to the
wire feeder conductor block. Refer to the
Accessories Section for wire feeder connection
instructions.

WELDING OPERATION

Familiarize yourself with the controls on the Invertec
STT II before beginning to weld.

Familiarize yourself with the operating manual for the
wire feeder and the wire feeder controls before begin­ning to weld.

Set the Wire Size and Wire Type selection switches per
the appropriate wire. Refer to “Operational Features
and Controls” in this section for the function of these
switches.

OPERATION

B-6 B-6

INVERTEC STT

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WELDING PARAMETERS AND GUIDE­LINES

The Invertec STT II is neither a constant current (CC)
nor a constant voltage (CV) power source. In general,
wire diameter will be increased one size compared to
conventional (CV) power sources. The larger the wire
diameter the higher the deposition rate (Up to 1/16”).
Wire sizes below .035” are unnecessary for most appli­cations. The Invertec STT II is a current controlled
machine which is capable of changing the electrode
current quickly in order to respond to the instantaneous
requirements of the arc and optimize performance.
By sensing changes in welding current, and hence the
electrode state, the power source will supply varying
output currents to minimize spatter. The Peak and
Background currents are two such current outputs that
can be adjusted.

Wire Feed Speed controls the deposition rate. Peak
Current controls the Arc Length. Background Current
controls the Bead Contour. And Tailout increases
Power in the Arc.

PEAK CURRENT

The Peak Current control acts similar to an “arc pinch”
control. Peak current serves to establish the arc length
and promote good fusion. Higher peak current levels
will cause the arc to broaden momentarily while
increasing the arc length. If set too high, globular type
transfer will occur. Setting this level to low will cause
instability and wire stubbing. In practice, this current
level should be adjusted for minimum spatter and pud­dle agitation.

Adjust Arc Length

with Peak Current

Note: In 100% CO2shielding gas applications the peak
current level should be set greater than in a corre-

sponding application using a gas blend with a high per­centage of Argon. Longer initial arc lengths with 100%
CO2are required to reduce spatter.

BACKGROUND CURRENT

The Background Current provides the control for the
overall heat input to the weld. Adjusting this level too
high will cause a large droplet to form and globular type
transfer to occur resulting in increased spatter.

Adjusting this level to low will cause wire stubbing and
also poor wetting of the weld metal. This is similar to a
low voltage setting on a standard CV machine

Adjust Bead Shape

using Background Current

Note: Background Current levels for applications using
100% CO2

is less than similar procedures involving gas
blends with high percentages of Argon. This is a result
of the greater heat generated in the 100% CO

2 arc.

(100% CO2 is 35 volts/cm and 100% Argon is 20
volts/cm. 75% Argon, 25% CO

2 is about 24 volts/cm.

Contact

Tip to W

ork Distance

HOT START

The Hot Start control can be set to enhance establish­ing the arc and provide the capability of increasing the
heat at the start of the weld to compensate for a cold
work piece. Hot start adjusts the time that additional
current is applied during the starting of the arc. Refer to
“Operational Features and Controls” in this section
for a description of this control.

TAILOUT

The tail out provides additional heat without the molten
droplet becoming too large. Increase as necessary to
add “Heat” to the arc without increasing arc length.
(This will allow for faster travel speeds and produce
improved wetting). As tailout is increased, the peal
and/or background current is usually reduced.

WELDING ARC PERFORMANCE

For optimum spatter reduction, the arc should be con­centrated on the puddle.

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OPERATION

B-7 B-7

INVERTEC STT

WELDING PROCEDURES FOR STT II -

(Steel) Horizontal Fillet (See Table B.1 and B.2)

Table B.1

100% CO

2

Gas Shield (Set for Steel Mode)

Table B.2

75% CO

2

- 25% Ar Gas Shield (Set for Steel Mode)

(Stainless Steel) Horizontal Fillet
(See Table B.3 and B.4)

Table B.3

90% He, 7.5% Ar, 2.5% CO

2

Gas Shield (Set for Steel Mode)

Table B.4

98% Ar, 2% O

2

Gas Shield (Set for Stainless Steel Mode)

45°

END VIEW

75°

FRONT VIEW

DIRECTION

OF

TRAVEL

75°

TOP VIEW

DIRECTION

OF

TRAVEL

Plate Thickness “ (mm) 20 ga 14 ga 10 ga

(0.9) (2.0) (3.25)

Electrode size “ (mm) 0.035 0.045 0.045

(0.9) (1.1) (1.1)

WFS “/min (m/min) 100 100 170

(2.5) (2.5) (4.2)
Peak Current 220 260 280
Background Current 30 40 65
Tailout setting 3 7 5
Average Amperage 60 105 120
Travel Speed “/min 12 12 12

(m/min) (0.3) (0.3) (0.3)
Gas Flow cfh (L/min) 25 (12)
Electrical Stickout “ 1/4 - 3/8

(mm) (6.4 - 10)

Plate Thickness “ (mm) 20 ga 14 ga 10 ga

(0.9) (2.0) (3.25)

Electrode size “ (mm) 0.035 0.045 0.045

(0.9) (1.1) (1.1)

WFS “/min (m/min) 100 100 120

(2.5) (2.5) (3.0)
Peak Current 225 270 310
Background Current 40 65 70
Tailout setting 8 4 6
Average Amperage 70 110 130
Travel Speed “/min 12 12 12

(m/min) (0.3) (0.3) (0.3)
Gas Flow cfh (L/min) 25 (12)
Electrical Stickout “ 1/4 - 3/8

(mm) (6.4 - 10)

45°

END VIEW

75°

FRONT VIEW

DIRECTION

OF

TRAVEL

75°

TOP VIEW

DIRECTION

OF

TRAVEL

Plate Thickness “ (mm) 20 ga 14 ga 10 ga

(0.9) (2.0) (3.25)

Electrode size “ (mm) 0.035 0.045 0.045

(0.9) (1.1) (1.1)

WFS “/min (m/min) 100 130 170

(2.5) (3.3) (4.2)
Peak Current 165 210 250
Background Current 35 60 85
Tailout setting 7 7 4
Average Amperage 40 95 120
Travel Speed “/min 12 16 16

(m/min) (0.3) (0.4) (0.4)
Gas Flow cfh (L/min) 25 (12)
Electrical Stickout “ 1/4 - 3/8

(mm) (6.4 - 10)

Plate Thickness “ (mm) 20 ga 14 ga 10 ga

(0.9) (2.0) (3.25)

Electrode size “ (mm) 0.035 0.045 0.045

(0.9) (1.1) (1.1)

WFS “/min (m/min) 100 130 170

(2.5) (3.3) (4.2)
Peak Current 145 190 280
Background Current 45 95 95
Tailout setting 7 8 7
Average Amperage 60 120 150
Travel Speed “/min 12 12 12

(m/min) (0.3) (0.3) (0.3)
Gas Flow cfh (L/min) 25 (12)
Electrical Stickout “ 1/4 - 3/8

(mm) (6.4 - 10)

NOTES

B-8 B-8

INVERTEC STT

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TABLE OF CONTENTS

- ACCESSORIES -

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

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

LN-742 Wire Feeder Connection Instructions.............................................................................C-3

Connection Diagram ...................................................................................................................C-4

Section C-1 Section C-1

INVERTEC STT

ACCESSORIES

C-2 C-2

INVERTEC STT

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STT control board to accept PEAK and BACK­GROUND inputs on this connector rather than from
the front panel controls. If this short is removed, the
front panel controls will be active. By adding a switch
between pins “J” and “B” a “LOCAL/REMOTE” con­trol switch can be created. (Switch open for “local”
and closed for “remote”)

3. For robotic control of the PEAK CURRENT, a 0 to

+10 volt DC signal is applied between pins “A” and
“G” with + applied to pin “G”. The BACKGROUND
CURRENT is controlled with a similar signal applied
between pins “A” and “C” with + applied to pin “C”.
In this application pins “J” and “B” must be shorted
as described in 2 above.

NOTE: These analog signals should be isolated
from the robot circuitry to prevent interference.

4. The trigger switch is connected between pins “D”

and “F”. These connections are in parallel with the
trigger switch from the wire feeder.

5. The digital meters for PEAK and BACKGROUND

currents will show preset values in both local and
remote operation.

OPTIONS / ACCESSORIES

K940 SENSE LEADS: These leads are used to accu-

rately sense arc voltage. One set is required for each
STT II power source. A 10 ft and 25 ft set are provid­ed as standard with the machine. Additional sets are
available in 10 ft (K940-10), 25 ft (K940-25) and 50 ft
(K940-50) lengths.

K942-1 REMOTE CONTROL: Allows remote adjust­ment of Peak and Background Current settings.

REMOTE RECEPTACLE (For optional remote interface,
Connection to the STT-10 Wire Feeder or Robotic Control)

1. The 10 pin MS connector labeled “Remote Control”
located on the front panel of the STT is used for
remote control of the power source. Control for the
PEAK (PB pot) and BACKGROUND (BG pot) cur­rent along with the trigger switch is provide through
this connector.

2. Refer to figure C.1 below for details about the
remote receptacle (J38). Note that pins “J” and “B”
are shorted together This “short circuit” tells the

+ ARC

- ARC

1
2

3
4

VOLTAGE
SENSE
CONNECTION

J19

290

291

(+)

(-)

J
B

C
G
A

D

F

H

E
I

TRIGGER

GND

BG

PB

10K

10K

OPTIONAL
REMOTE
INTERFACE

223

7

J38

33C

1

2
3
4

J37

8

6
1

5

8

4

3
2

212C

43A

212B

32C

3

1

2

10

9

12

4

11

J38

REMOTE
PROTECTION BOARD

PORTION OF G3136 WIRING DIAGRAM
REFER TO ACTUAL DIAGRAM PASTED INSIDE YOUR MACHINE

N

ELECTRODE SENSE LEAD

290A

J39

WIRE

FEEDER

ACCESSORIES

C-3 C-3

INVERTEC STT

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LN-742 or STT-10 WIRE FEEDER
CONNECTION INSTRUCTIONS

The LN-742 or STT-10 is the recommended wire feed­er for use with the Invertec STT II. Refer to the LN­742 or STT-10 Operator Manual for Wire Feed
Operation. Refer to Figure C.2 or C.3 and follow the
instructions below to connect the LN-742 or STT-10.

1. Turn the Invertec STT II power off.

2. Connect the ARC SENSE LEAD MS connector to
the mating connector on STT II front panel.

3. Connect the electrode lead (Twist-Mate) to (+) out­put terminal on STT II.

4. Connect the other end of electrode lead (Step #3)
and the ARC SENSE LEAD (lead with ring lug, step
#2) together to the gun block on the LN 742.

5. Connect work lead between STT (-) terminal and the
work piece.

6. Connect the ARC SENSE LEAD “WORK” (lead with
alligator clip) to work piece.

NOTE: For best welding performance make this

connection as close as possible to the
welding arc.

7. Connect the wire feeder control cable between the
LN-742 or STT-10 and the 14-pin Wire Feeder
Receptacle on the STT II. For the STT-10 Wire
Feeder: Connect the second wire feeder control
cable between the STT-10 and the 10-pin Remote
Receptacle on the STT II.

M17657

ARC SENSE LEAD
’ELECT"

CONNECT ELECTRODE LEAD AND "ELECT"
ARC SENSE LEAD TOGETHER TO ELECTRODE
TERMINAL OF WIRE FEEDER.

ELECTRODE LEAD

Only qualified persons should install,
use or service this machine.

WIRE FEEDER

LN 742
LN7 GMA
LN9 GMA
NA5R
NA5

WARNING

ELECTRIC
SHOCK
CAN KILL

Turn off input power to the Welding
Power source using the disconnnect
switch at the fuse box before
connecting the wire feeder.

REMOTE RECEPTACLE

WORK

WORK LEAD

CONTROL, ELECTRODE, ARC SENSE "ELECT"
AND ARC SENSE "WORK" CABLES SHOULD
BE TAPED TOGETHER.

WIRE FEEDER

CONTROL CABLE

ARC SENSE LEAD "WORK"
(SHOULD BE LOCATED
AS CLOSE AS POSSIBLE
TO THE WELDING ARC.)

CRM after 6-10-96

FIGURE C.2 LN-742 to STT II CONNECTION

WARNING

ELECTRIC SHOCK can kill.

• Only qualified personnel should perform
this installation.

•Turn the input power OFF at the discon­nect switch or fuse box before connecting
the wire feeder

C-4 C-4

INVERTEC STT

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ACCESSORIES

CONNECTION DIAGRAM - INVERTEC STT II

4-9-99

M17657-3

CABLES AND LEADS SHOULD

ELECTRODE LEAD

BE TAPED TOGETHER.

WORK

(SHOULD BE LOCATED
AS CLOSE AS POSSIBLE

FEEDER

REMOTE

REMOTE

ELECTRODE LEAD

TO THE WELDING ARC)

WORK LEAD

WIRE FEEDER

WIRE FEEDER CONTACT

ELECTRODE SENSE LEAD
IS BOLTED TOGETHER WITH
ELECTRODE LEAD ON THE

BLOCK

STT-10

WIRE FEEDER

WARNING

Turn off input power to the Welding
Power source using the disconnnect
switch at the fuse box before
connecting the wire feeder.

Only qualified persons should install,

ELECTRIC

use or service this machine.

SHOCK
CAN KILL

WIRE

ARC SENSE LEAD "WORK"

FIGURE C.3 STT-10 to STT II CONNECTION

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Section D-1 Section D-1

INVERTEC STT

TABLE OF CONTENTS

-MAINTENANCE-

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

Input Filter Capacitor Discharge Procedure................................................................................D-2

Preventive Maintenance .............................................................................................................D-3

Major Component Locations.......................................................................................................D-4

MAINTENANCE

D-2 D-2

INVERTEC STT

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WARNING

Failure to follow this
capacitor discharge proce­dure can result in electric
shock.

INPUT FILTER CAPACITOR
DISCHARGE PROCEDURE

1. Turn off input power or disconnect input
power lines.

2. Remove hex head screws from side and
top of machine and remove wrap-around
machine cover.

3. Be careful not to make contact with the
capacitor terminals that are located in the
center of the Switch Boards.

4. Obtain a high resistance and high
wattage resistor (25-1000 ohms and 25
watts minimum). This resistor is not sup­plied with machine. NEVER USE A

SHORTING STRAP FOR THIS PROCE­DURE.

5. Locate the two capacitor terminals (large
hex head cap screws) shown in Figure
D.1.

6. Use safety glasses, electrically insulated
gloves and insulated pliers. Hold body of
the resistor and connect resistor leads
across the two capacitor terminals. Hold
resistor in place for 10 seconds. DO NOT
TOUCH CAPACITOR TERMINALS WITH
YOUR BARE HANDS.

7. Repeat discharge procedure for capaci-

tor on other side of machine.

8. Check voltage across terminals of all
capacitors with a DC voltmeter. Polarity
of capacitor terminals is marked on PC
board above terminals. Voltage should be
zero. If any voltage remains, repeat this
capacitor discharge procedure.

FIGURE D.1 — LOCATION OF INPUT FILTER CAPACITOR TERMINALS.

MAINTENANCE

D-3 D-3

INVERTEC STT

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PREVENTIVE MAINTENANCE

1. Perform the following preventive mainte­nance procedures at least once every six
months. It is good practice to keep a pre­ventive maintenance record; a record tag
attached to the machine works best.

2. Remove the machine wraparound cover
and perform the input filter capacitor dis­charge procedure (detailed at the begin­ning of this chapter).

3. Clean the inside of the machine with a
low pressure airstream. Be sure to clean
the following components thoroughly.

• Power Switch, Driver, Protection, and

Control printed circuit boards

• Power Switch

• Main Transformer

• Input Rectifier

• Heat Sink Fins

• Input Filter Capacitors

• Output Terminals

• Lower base compartment

4. Examine capacitors for leakage or oozing.
Replace if needed.

5. Examine wraparound cover for dents or
breakage. Repair as needed. Cover must
be kept in good condition to assure high
voltage parts are protected and correct
spacings are maintained.

6. Check electrical ground continuity. Using
an ohmmeter, measure resistance
between either output stud and an unpaint­ed surface of the machine case. Meter
reading should be 500,000 ohms or more.
If meter reading is less than 500,000
ohms, check for electrical components that
are not properly insulated from the case.
Correct insulation if needed.

7. Replace machine cover and screws.

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MAINTENANCE

D-4 D-4

INVERTEC STT

12

4

17

5

6

9

8

7

10

16

15

13

18

14

19

11

1

3

2

FIGURE D.2 – MAJOR COMPONENT LOCATIONS

1. BASE ASSEMBLY

2. REAR NAMEPLATE

3. RESISTORS

4. FAN SHROUD ASSEMBLY

5. PROTECTION PC BOARD

6. DRIVER PC BOARD

7. CONTROL BOX

8. CONTROL PC BOARD

9. BLEEDER RESISTORS

10. RECONNECT PANEL

11. IGBT OR DARLINGTON MODULE

12. WRAPAROUND ASSEMBLY

13. CASE FRONT ASSEMBLY

14. OUTPUT TERMINALS

15. OUTPUT CHOKE ASSEMBLY

16. TRANSFORMER ASSEMBLY

17. OUTPUT RECTIFIER ASSEMBLY

18. AUXILIARY TRANSFORMER

19. FET HEAT SINK ASSEMBLY

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Section E-1 Section E-1

INVERTEC STT

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

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

Input Voltage..........................................................................................................................E-2

Reconnect, Protection Board, Rectification and Precharge ..................................................E-3

Switch Boards........................................................................................................................E-4

Main Transformer, Output Rectification and Choke...............................................................E-5

Control Board, IGBT Drive and Module.................................................................................E-6

Power Board ..........................................................................................................................E-7

Remote Protection Board ......................................................................................................E-7

Field Effect Transistor (FET) Operation.................................................................................E-8

Pulse Width Modulation.........................................................................................................E-9

Minimum Output ..............................................................................................................E-9

Maximum Output .............................................................................................................E-9

Protective Circuits................................................................................................................E-10

Overload Protection.......................................................................................................E-10

Thermal Protection ........................................................................................................E-10

TABLE OF CONTENTS

-THEORY OF OPERATION SECTION-

POSITIVE

OUTPUT

TERMINAL

TERMINAL

OUTPUT

NEGATIVE

CONTROL BOARD

IGBT
DRIVER
BOARD

P
O
W
E
R

B
O
A
R
D

FAN

TRANS

T1

TRANS

T4

S
W

I
T
C
H

B

O

A
R
D

S
W

I

T
C
H

B

O

A
R
D

R
E
C
O
N
N
E
C
T

P
R
O
T
E
C
T

I
O
N

INPUT

RECTIFIER

LINE

SWITCH

CR1

CR2

B
O

A
R
D

D
R

I

V
E
R

B
O

A
R
D

PRE -

CHARGE

PRE -

CHARGE

CHOKE

CURRENT

SENSOR

IGBT

MODULE

1 OHM

PEAK

CURRENT

METER

BACK-

METER

PEAK
CURRENT
CONTROL

BACK-

CONTROL

HOT

START

CONTROL

WIRE

SIZE

SWITCH

WIRE
TYPE

SWITCH

VOLTAGE

SENSING

RECEPTACLE

REMOTE

CONTROL

RECEPTACLE

WIRE

RECEPTACL

E

FEEDER

R

E
M
O

T

E

P
R
O

T

E
C
T

I
O

N

B
O
A

R

D

CURRENT

TRANS

T3

MAIN

TRANSFORMER

T2

115
VAC

18

VAC

2
4
V
A
C

"A"

LEAD

15VDC

T
H
E
R
M
O
S
T
A
T

CURRENT FEEDBACK

42VAC

VOLTAGE FEEDBACK

10VAC AND 6VAC

D
R

I
V
E

S

I
G

N

A
L

36VAC

GUN TRIGGER

LESS THAN 1VDC

PWM SIGNAL

PULSE TRANSFORMER SIGNAL

GROUND

GROUND

FET

FET

FET

FET

CAP

CAP

TAILOUT

CONTROL

(STT II ONLY)

FIGURE E.1 – INVERTEC STT

GENERAL DESCRIPTION

The Invertec STT is a 225 ampere, inverter based, arc
welding power supply specifically designed for the
Surface Tension Transfer (STT) welding process. It
cannot be classified as either a constant current (CC)
or a constant voltage (CV) machine. The STT pro­duces current of a desired waveform to reduce spatter
and fumes. The STT process is optimized for short ­circuit GMAW welding only.

INPUT VOLTAGE

The Invertec STT can be connected for a variety of
three-phase voltages. The initial input power is applied
to the STT through a line switch located on the front of
the machine. The AC input voltage is applied to the
input rectifier and the T1 auxiliary transformer. The T1
transformer develops the appropriate AC voltages to
operate the cooling fan, the power and control boards.
The T1 transformer also supplies primary voltage to the
T4 auxiliary transformer as well as 42 VAC to an exter­nal wire feeder. The T4 transformer supplies power to
the IGBT drive board and the control board.

THEORY OF OPERATION

E-2 E-2

INVERTEC STT

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FIGURE E.2 – INPUT VOLTAGE

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

POSITIVE

OUTPUT

TERMINAL

TERMINAL

OUTPUT

NEGATIVE

CONTROL BOARD

IGBT
DRIVER
BOARD

P
O
W
E
R

B
O
A
R
D

FAN

TRANS

T1

TRANS

T4

S
W

I
T
C
H

B
O
A
R
D

S
W

I

T
C
H

B
O
A
R
D

R
E
C
O
N
N
E
C
T

P
R
O
T
E
C
T
I
O
N

INPUT

RECTIFIER

LINE

SWITCH

CR1

CR2

B
O

A
R
D

D
R

I

V
E
R

B
O

A
R
D

PRE -

CHARGE

PRE -

CHARGE

CHOKE

CURRENT

SENSOR

IGBT

MODULE

1 OHM

PEAK

CURRENT

METER

BACK-

METER

PEAK
CURRENT
CONTROL

BACK-

CONTROL

HOT

START

CONTROL

WIRE
SIZE

SWITCH

WIRE

TYPE

SWITCH

VOLTAGE

SENSING

RECEPTACLE

REMOTE
CONTROL

RECEPTACLE

WIRE

RECEPTACL

E

FEEDER

R
E

M

O
T
E

P
R
O
T
E
C
T
I
O
N

B
O
A

R

D

CURRENT

TRANS

T3

MAIN

TRANSFORMER

T2

115
VAC

18

VAC

2
4
V
A
C

"A"

LEAD

15VDC

T
H
E
R
M
O
S
T
A
T

CURRENT FEEDBACK

42VAC

VOLTAGE FEEDBACK

10VAC AND 6VAC

D
R

I
V
E

S

I
G

N
A
L

36VAC

GUN TRIGGER

LESS THAN 1VDC

PWM SIGNAL

PULSE TRANSFORMER SIGNAL

GROUND

GROUND

FET

FET

FET

FET

CAP

CAP

TAILOUT

CONTROL

(STT II ONLY)

RECONNECT, PROTECTION
BOARD, RECTIFICATION AND
PRECHARGE

The reconnect panel allows the user to switch to low or
high input voltage to match the input line voltage. The
AC input voltage is rectified and applied to the driver
board. The driver board contains precharging circuitry
for safe charging of the input filter capacitors. Once the
capacitors are precharged, the input relays are ener­gized, connecting full input power to the input filter
capacitors. The protection board monitors the capaci­tors for voltage balance and/or overvoltage and will de­energize the input relays and precharge circuitry if
either occurs. The machine output will be disabled.

THEORY OF OPERATION

E-3 E-3

INVERTEC STT

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

FIGURE E.3 – RECONNECT, PROTECTION BOARD, RECTIFICATION AND PRECHARGE

POSITIVE

OUTPUT

TERMINAL

TERMINAL

OUTPUT

NEGATIVE

CONTROL BOARD

IGBT
DRIVER
BOARD

P
O
W
E
R

B
O
A
R
D

FAN

TRANS

T1

TRANS

T4

S
W

I
T
C
H

B
O
A
R
D

S
W

I
T
C
H

B
O
A
R
D

R
E
C
O
N
N
E
C
T

P
R
O
T
E
C
T

I
O
N

INPUT

RECTIFIER

LINE

SWITCH

CR1

CR2

B
O

A
R
D

D
R

I

V
E
R

B
O

A
R
D

PRE -

CHARGE

PRE -

CHARGE

CHOKE

CURRENT

SENSOR

IGBT

MODULE

1 OHM

PEAK

CURRENT

METER

BACK-

METER

PEAK
CURRENT
CONTROL

BACK-

CONTROL

HOT

START

CONTROL

WIRE
SIZE

SWITCH

WIRE
TYPE

SWITCH

VOLTAGE
SENSING

RECEPTACLE

REMOTE

CONTROL

RECEPTACLE

WIRE

RECEPTACL

E

FEEDER

R

E
M
O

T

E

P
R
O

T

E
C
T

I
O

N

B
O
A

R

D

CURRENT

TRANS

T3

MAIN

TRANSFORMER

T2

115
VAC

18

VAC

2
4
V
A
C

"A"

LEAD

15VDC

T
H
E
R
M
O
S
T
A
T

CURRENT FEEDBACK

42VAC

VOLTAGE FEEDBACK

10VAC AND 6VAC

D
R

I
V
E

S
I

G

N
A
L

36VAC

GUN TRIGGER

LESS THAN 1VDC

PWM SIGNAL

PULSE TRANSFORMER SIGNAL

GROUND

GROUND

FET

FET

FET

FET

CAP

CAP

TAILOUT

CONTROL

(STT II ONLY)

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THEORY OF OPERATION

E-4 E-4

INVERTEC STT

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

FIGURE E.4 – SWITCH BOARDS

SWITCH BOARDS

There are two switch boards in the Invertec STT, each
containing an input filter capacitor. The capacitors are
connected in parallel when the machine is connected
for "low" input voltage. The capacitors are connected
in series when the reconnect switch is configured for
"high" input voltage. When the capacitors are fully
charged, they act as power supplies for the switch
boards. The switch boards contain the Field Effect
Transistors (FETs) which, when switched on, supply
the main transformer primary windings with DC current
flow. See Field Effect Transistor (FET) Operation
discussion and diagrams. See Figure E.4.

POSITIVE

OUTPUT

TERMINAL

TERMINAL

OUTPUT

NEGATIVE

CONTROL BOARD

IGBT
DRIVER
BOARD

P
O
W
E
R

B
O
A
R
D

FAN

TRANS

T1

TRANS

T4

S
W

I
T
C
H

B
O
A
R
D

S
W

I

T
C
H

B
O
A
R
D

R
E
C
O
N
N
E
C
T

P
R
O
T
E
C
T

I
O
N

INPUT

RECTIFIER

LINE

SWITCH

CR1

CR2

B
O

A
R
D

D
R

I

V
E
R

B
O

A
R
D

PRE -

CHARGE

PRE -

CHARGE

CHOKE

CURRENT

SENSOR

IGBT

MODULE

1 OHM

PEAK

CURRENT

METER

BACK-

METER

PEAK
CURRENT
CONTROL

BACK-

CONTROL

HOT

START

CONTROL

WIRE
SIZE

SWITCH

WIRE
TYPE

SWITCH

VOLTAGE
SENSING

RECEPTACLE

REMOTE

CONTROL

RECEPTACLE

WIRE

RECEPTACL

E

FEEDER

R

E
M
O

T

E

P
R
O

T

E
C
T

I
O

N

B
O
A

R

D

CURRENT

TRANS

T3

MAIN

TRANSFORMER

T2

115
VAC

18

VAC

2
4
V
A
C

"A"

LEAD

15VDC

T
H
E
R
M
O
S
T
A
T

CURRENT FEEDBACK

42VAC

VOLTAGE FEEDBACK

10VAC AND 6VAC

D
R

I
V
E

S
I

G

N
A
L

36VAC

GUN TRIGGER

LESS THAN 1VDC

PWM SIGNAL

PULSE TRANSFORMER SIGNAL

GROUND

GROUND

FET

FET

FET

FET

CAP

CAP

TAILOUT

CONTROL

(STT II ONLY)

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THEORY OF OPERATION

E-5 E-5

INVERTEC STT

FIGURE E.5 – MAIN TRANSFORMER, OUTPUT RECTIFICATION AND CHOKE

MAIN TRANSFORMER, OUTPUT
RECTIFICATION AND CHOKE

Each switch board works as a switch pair. Each board
feeds a separate, oppositely wound primary winding of
the main transformer. The opposite directions of cur­rent flow through the main transformer primary and the
offset timing of the switch boards induce an AC square
wave output signal at the secondary of the main trans­former.

The DC current flow through each primary winding,
which is monitored by the current transformer T3, is
redirected or "clamped" back to each respective input
capacitor when the FETs are turned off. This is need­ed due to the inductance of the transformer primary
windings. The cross coupling of the primaries along
with the clamping action of the diode maintain capaci­tor balance when they are connected in the series (high
voltage) input configuration.

The firing of both switch board pairs occurs during
halves of 50 microsecond intervals, creating a constant
20 KHZ output.

The AC output from the main transformer secondary is
rectified to a DC output and is applied through a stabi­lizer output choke, current sensor, IGBT module and
remote protection board to the output terminals.

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

POSITIVE

OUTPUT

TERMINAL

TERMINAL

OUTPUT

NEGATIVE

CONTROL BOARD

IGBT
DRIVER
BOARD

P
O
W
E
R

B
O
A
R
D

FAN

TRANS

T1

TRANS

T4

S
W

I
T
C
H

B
O
A
R
D

S
W

I

T
C
H

B
O
A
R
D

R
E
C
O
N
N
E
C
T

P
R
O
T
E
C
T
I
O
N

INPUT

RECTIFIER

LINE

SWITCH

CR1

CR2

B
O

A
R
D

D
R

I

V
E
R

B
O

A
R
D

PRE -

CHARGE

PRE -

CHARGE

CHOKE

CURRENT

SENSOR

IGBT

MODULE

1 OHM

PEAK

CURRENT

METER

BACK-

METER

PEAK
CURRENT
CONTROL

BACK-

CONTROL

HOT

START

CONTROL

WIRE
SIZE

SWITCH

WIRE

TYPE

SWITCH

VOLTAGE

SENSING

RECEPTACLE

REMOTE
CONTROL

RECEPTACLE

WIRE

RECEPTACL

E

FEEDER

R
E

M

O
T
E

P
R
O
T
E
C
T
I
O
N

B
O
A

R

D

CURRENT

TRANS

T3

MAIN

TRANSFORMER

T2

115
VAC

18

VAC

2
4
V
A
C

"A"

LEAD

15VDC

T
H
E
R
M
O
S
T
A
T

CURRENT FEEDBACK

42VAC

VOLTAGE FEEDBACK

10VAC AND 6VAC

D
R

I
V
E

S

I
G

N

A

L

36VAC

GUN TRIGGER

LESS THAN 1VDC

PWM SIGNAL

PULSE TRANSFORMER SIGNAL

GROUND

GROUND

FET

FET

FET

FET

CAP

CAP

TAILOUT

CONTROL

(STT II ONLY)

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THEORY OF OPERATION

E-6 E-6

INVERTEC STT

FIGURE E.6 – CONTROL BOARD, IGBT DRIVE AND MODULE

CONTROL BOARD, IGBT DRIVE
AND MODULE

The control board monitors the directives of the various
controls and compares these commands to the current
and voltage feedback information received from the
current sensor and voltage sensing receptacle. This
data is processed and the suitable PWM signal is sent
to the power board. (See Pulse Width Modulation
discussion).

The control board also determines when the IGBT
module should be switched OFF to reduce weld spat­ter and fumes. The appropriate signal is sent to the
IGBT drive board which then applies, or removes, the
gate drive signal to the IGBT module. When the IGBT
module is in the OFF state, the welding current must
pass through the one ohm resistance. This reduces
the current and, subsequently, spatter and fumes.

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

POSITIVE

OUTPUT

TERMINAL

TERMINAL

OUTPUT

NEGATIVE

CONTROL BOARD

IGBT
DRIVER
BOARD

P
O
W
E
R

B
O
A
R
D

FAN

TRANS

T1

TRANS

T4

S
W

I
T
C
H

B
O
A
R
D

S
W

I

T
C
H

B
O
A
R
D

R
E
C
O
N
N
E
C
T

P
R
O
T
E
C
T

I
O
N

INPUT

RECTIFIER

LINE

SWITCH

CR1

CR2

B
O

A
R
D

D
R

I

V
E
R

B
O

A
R
D

PRE -

CHARGE

PRE -

CHARGE

CHOKE

CURRENT

SENSOR

IGBT

MODULE

1 OHM

PEAK

CURRENT

METER

BACK-

METER

PEAK
CURRENT
CONTROL

BACK-

CONTROL

HOT

START

CONTROL

WIRE
SIZE

SWITCH

WIRE
TYPE

SWITCH

VOLTAGE
SENSING

RECEPTACLE

REMOTE

CONTROL

RECEPTACLE

WIRE

RECEPTACL

E

FEEDER

R

E
M
O

T

E

P
R
O

T

E
C
T

I
O

N

B
O
A

R

D

CURRENT

TRANS

T3

MAIN

TRANSFORMER

T2

115
VAC

18

VAC

2
4
V
A
C

"A"

LEAD

15VDC

T
H
E
R
M
O
S
T
A
T

CURRENT FEEDBACK

42VAC

VOLTAGE FEEDBACK

10VAC AND 6VAC

D
R

I
V
E

S
I

G

N
A
L

36VAC

GUN TRIGGER

LESS THAN 1VDC

PWM SIGNAL

PULSE TRANSFORMER SIGNAL

GROUND

GROUND

FET

FET

FET

FET

CAP

CAP

TAILOUT

CONTROL

(STT II ONLY)

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THEORY OF OPERATION

E-7 E-7

INVERTEC STT

FIGURE E.7 – POWER BOARD AND REMOTE PROTECTION BOARD

POWER BOARD

The power board creates a pulse transformer drive sig­nal, which is derived from the PWM signal received
from the control board. See Pulse Width Modulation
discussion. This drive signal is applied to the primary
winding of the pulse transformer, which is located on
the driver board. The pulse transformer secondary
windings generate the proper gate pulse for the switch
board FETs. See Field Effect Transistor (FET)

Operation.

The power board supplies a 15VDC supply voltage for
the control board and also powers the input relays
(CR1 and CR2).

REMOTE PROTECTION BOARD

The remote protection board provides noise suppres­sion and by-pass filtering to protect the internal circuit­ry of the STT machine.

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

POSITIVE

OUTPUT

TERMINAL

TERMINAL

OUTPUT

NEGATIVE

CONTROL BOARD

IGBT
DRIVER
BOARD

P
O
W
E
R

B
O
A
R
D

FAN

TRANS

T1

TRANS

T4

S
W
I
T
C
H

B
O
A
R
D

S
W

I
T
C
H

B
O
A
R
D

R
E
C
O
N
N
E
C
T

P
R
O
T
E
C
T

I
O
N

INPUT

RECTIFIER

LINE

SWITCH

CR1

CR2

B
O

A
R
D

D
R

I

V
E
R

B
O

A
R
D

PRE -

CHARGE

PRE -

CHARGE

CHOKE

CURRENT

SENSOR

IGBT

MODULE

1 OHM

PEAK

CURRENT

METER

BACK-

METER

PEAK
CURRENT
CONTROL

BACK-

CONTROL

HOT

START

CONTROL

WIRE
SIZE

SWITCH

WIRE
TYPE

SWITCH

VOLTAGE

SENSING

RECEPTACLE

REMOTE

CONTROL

RECEPTACLE

WIRE

RECEPTACL

E

FEEDER

R
E

M

O
T
E

P
R
O
T
E
C
T

I
O
N

B
O
A

R

D

CURRENT

TRANS

T3

MAIN

TRANSFORMER

T2

115
VAC

18

VAC

2
4
V
A
C

"A"

LEAD

15VDC

T
H
E
R
M
O
S
T
A
T

CURRENT FEEDBACK

42VAC

VOLTAGE FEEDBACK

10VAC AND 6VAC

D
R

I
V
E

S

I
G

N
A

L

36VAC

GUN TRIGGER

LESS THAN 1VDC

PWM SIGNAL

PULSE TRANSFORMER SIGNAL

GROUND

GROUND

FET

FET

FET

FET

CAP

CAP

TAILOUT

CONTROL

(STT II ONLY)

FIELD EFFECT TRANSISTOR (FET)
OPERATION

An FET is a type of transistor. FETs are semiconduc­tors well suited for high-frequency switching.

Drawing A above shows an FET 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 FET may be connected to a voltage supply; but
since there is no conduction, the circuit will not supply
current to downstream components connected to the
source. The circuit is turned off like a light switch in the
OFF position.

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

THEORY OF OPERATIONS

E-8 E-8

INVERTEC STT

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SOURCE
TERMINAL

GATE
TERMINAL

DRAIN
TERMINAL

DRAIN (N)

N CHANNELSUBSTRATE (P)

SOURCE (N)

(0 VOLTS)

GATE
TERMINAL
(+ 6 VOLTS)

DRAIN (N)

ELECTRONS

SOURCE (N)

B. ACTIVE

A. PASSIVE

FIGURE E-8 – FIELD EFFECT TRANSISTOR OPERATION

PULSE WIDTH MODULATION

The term PULSE WIDTH MODULATION is used to
describe how much time is devoted to conduction in
the positive and negative portions of the cycle.
Changing the pulse width is known as MODULATION.
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 FET
is turned on and off for different durations during a
cycle. The top drawing above shows the minimum out­put signal possible over a 50-microsecond time period.

The positive portion of the signal represents one FET
group

1

conducting for 1 microsecond. The negative

portion is the other FET group

1

. The dwell time (off
time) is 48 microseconds (both FET groups off). 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 24 microseconds
each 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 dark area under the curve, the more power
is present.

THEORY OF OPERATION

E-9 E-9

INVERTEC STT

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MINIMUM OUTPUT

MAXIMUM OUTPUT

24

50

2

48

50

sec
sec

sec

sec

sec

sec

sec

24

sec

FIGURE E-9 – TYPICAL FET OUTPUTS

1

A FET group consists of the sets of FET modules grouped onto
one switch board.

PROTECTIVE CIRCUITS

Protective circuits are designed into the Invertec
machine to sense trouble and shut down the machine
before the trouble damages the internal machine com­ponents. Both overload and thermal protection circuits
are included.

OVERLOAD PROTECTION

The machine is electrically protected from producing
abnormally high output currents due to short electrode
“stick-out” or the nozzle shorting to the work. Should
the output current exceed 500 amps, an electronic pro­tection circuit will reduce the current to zero amps.
Five seconds after the “short” is removed the Invertec
STT will produce normal output.

A protection circuit is included to monitor the voltage
across input filter capacitors. In the event that the
capacitor voltage is too high, the protection circuit will
prevent output. The protection circuit may prevent out­put, if any of these circumstances occur:

1. Capacitor conditioning is required
(Required if machine has been off for prolonged
periods of time.)

2. Line surges over 500 VAC

3. Internal Component damage

4. Improper connections

THERMAL PROTECTION

Thermostats protect the machine from excessive oper­ating temperatures. Excessive temperatures may be
caused by a lack of cooling air or operating the
machine beyond the duty cycle and output rating. If
excessive operating temperature should occur, the
thermostat will prevent output voltage or current. The
meter will remain on during this time. (In addition, the
yellow thermo LED will light.)

Thermostats are self-resetting once the machine cools
sufficiently. If the thermostat shutdown was caused by
excessive output or duty cycle and the fan is operating
normally, the Power Switch may be left on and the
reset should occur within a 15-minute period. If the fan
is not turning or the air intake louvers were obstructed,
then the power must be switched off for 15 minutes in
order to reset. The fan problem or air obstruction must
also be corrected.

THEORY OF OPERATION

E-10 E-10

INVERTEC STT

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Section F-1 Section F-1

INVERTEC STT

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

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

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

Troubleshooting Guide .................................................................................................F4 - F-12

Te st Procedures...................................................................................................................F-13

T1 Auxiliary Transformer Test ........................................................................................F-13

T4 Auxiliary Transformer Test ........................................................................................F-19

Input Rectifier Test.........................................................................................................F-25

Capacitor Balance Test .................................................................................................F-29

Switch Board Test..........................................................................................................F-33

Snubber Resistors Test .................................................................................................F-37

Power Board Test ..........................................................................................................F-41

Protection Board Test ....................................................................................................F-45

Trigger Circuit Test ........................................................................................................F-49

Replacement Procedures ....................................................................................................F-53

IGBT Module Removal and Replacement.....................................................................F-53

Switch Board Replacement ...........................................................................................F-59

Capacitor Removal and Replacement Procedure.........................................................F-65

Output Rectifier Removal and Replacement.................................................................F-73

Retest After Repair...............................................................................................................F-77

TABLE OF CONTENTS

TROUBLESHOOTING & REPAIR SECTION

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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.

TROUBLESHOOTING & REPAIR

F-2 F-2

INVERTEC STT

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 two main categories: Output 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 wrap-around 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 chapter. 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.

WARNING

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

1-888-935-3877

.

OSCILLOSCOPE WARNING

Do not use oscilloscopes and other test equipment which are powered by 115 VAC. This equipment
should not be used with inverter-type machines, such as Invertec STT. There are high voltages pre­sent, which are “floating” off case ground (floating ground). Connecting the ground lead of a test probe
(which may be connected to the case of the test equipment) to a high voltage potential presents a shock
hazard as well as the possibility of damage to the equipment in question.

WARNING

CAUTION

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 static-shielding
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 electri-

cal 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.

TROUBLESHOOTING & REPAIR

F-3 F-3

INVERTEC STT

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PC BOARD TROUBLESHOOTING PROCEDURES

WARNING

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

Reusable
Container
Do Not Destroy

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TROUBLESHOOTING & REPAIR

F-4 F-4

INVERTEC STT

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

1-888-935-3877

.

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,

1-888-935-

3877

.

Machine has no open circuit volt­age. Wire feeds OK.

1. Check the control cable
between the feeder and the
STT unit. Make sure the #2 and
#4 leads are intact.

2. Put a jumper wire between Pins
"C" and "D" on the 14 pin
amphenol. If normal open cir­cuit voltage (85VDC) is
restored, the problem is in the
feeder control cable or the wire
feeder.

3. Make sure the reconnect switch
S7 is in the correct position for
the three-phase input voltage
being applied.

Do not switch reconnect switch
with input power applied to
machine.

1. Perform the T1 Auxiliary

Transformer Test.

2. Perform the T4 Auxiliary
Transformer Test.

3. Perform the Power Board Test.

4. Perform the Trigger Circuit

Test.

5. Perform Capacitor Balance
Test.

6. Perform the Protection Board
Test.

7. Perform the Switch Board
Test.

8. Check for loose or broken con­nections on the heavy current
carrying conductors (i.e., main
transformer, choke, output
diodes, IGBT module and out­put terminals).

9. The control PC board may be
faulty. Replace.

CAUTION

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TROUBLESHOOTING & REPAIR

F-5 F-5

INVERTEC STT

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

1-888-935-3877

.

PROBLEMS
(SYMPTOMS)

POSSIBLE AREAS OF
MISADJUSTMENT(S)

RECOMMENDED
COURSE OF ACTION

OUTPUT PROBLEMS

Machine has no welding output (no open circuit voltage), and the wire feeder does not feed wire when the gun trigger is pulled.

1. The 42VAC circuit breaker CB1
may be tripped. Reset if neces­sary.

2. Check the 4 amp slow blow fuse
located on the reconnect panel.
Replace if faulty.

3. Put a jumper between pins "A"
and "C" on the 5 pin amphenol
located on the LN-742 wire
feeder. If wire feeds, check the
gun trigger. Repair or replace if
necessary.

4. Check for the presence of
42VAC at pins "K" and "I" on the
14 pin amphenol. If the 42VAC
is present and the feeder does
not work, the problem is in the
feeder control cable or the wire
feeder.

1. If 42VAC is NOT present at pins
"K" and "I" on the 14 pin amphe­nol, perform the T1 Auxiliary

Transformer Test.

2. Check leads #43 and #212C for
loose or faulty connections
between the T1 auxiliary trans­former and the remote protec­tion board. See the Wiring
Diagram. Also check the conti­nuity through the remote protec­tion board to the 14 pin amphe­nol. See the Remote Protection
Board Schematic.

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TROUBLESHOOTING & REPAIR

F-6 F-6

INVERTEC STT

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

1-888-935-3877

.

PROBLEMS
(SYMPTOMS)

POSSIBLE AREAS OF
MISADJUSTMENT(S)

RECOMMENDED
COURSE OF ACTION

OUTPUT PROBLEMS

Machine is dead - no output - no fan - no display.

1. The power switch must be in the
"ON" position.

2. Check the input voltage. Make
sure all three phases are
applied to the machine.

3. With input power removed,
check that the input voltage set­up switch and jumper "A" (the
reconnect auxiliary jumper) are
in the proper position for the
input voltage being used.

4. With input power removed,
check the continuity of the 4
amp slow blow fuse located on
the reconnect panel.

1. The input power switch (S1)
may be faulty. Check or
replace.

2. Perform the T1 Auxiliary

Transformer Test.

No output or reduced output the first time power is applied to the machine.

1. Check input voltages, fuses and
input voltage reconnect proce­dures. See the Installation
section.

2. If high input voltage (380VAC or
higher) is applied, the capaci­tors may need conditioning. Let
the "unloaded" machine idle for
30 minutes.

1. Contact the Lincoln Electric
Service Department.

1-888-935-

3877

.

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TROUBLESHOOTING & REPAIR

F-7 F-7

INVERTEC STT

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

1-888-935-3877

.

PROBLEMS
(SYMPTOMS)

POSSIBLE AREAS OF
MISADJUSTMENT(S)

RECOMMENDED
COURSE OF ACTION

OUTPUT PROBLEMS

No output. Main fuses are open, indicating excessive current draw.

1. With the input power removed,
inspect input leads for possible
shorts or grounds or miscon­nections.

2. Install new fuses and reapply
power. If fuses open again,
contact your local Lincoln
Authorized Field Service
Facility.

1. Check the input power switch
(S1) and the reconnect switch
for "shorted" or "grounded"
wires or connections.

2. Perform the Input Rectifier

Test.

3. Perform the Switch Board
Test.

Machine loses output when gun trigger is pulled or arc is struck. Machine output returns after a few seconds and trigger is pulled again. The thermal indicator light is lit.

1. The overcurrent sensor is acti­vated, indicating that too much
output current is being drawn
from the machine. Reduce
welding current demands or
remove the "fault" in welding
cables.

2. Make sure that the gun tip is not
"shorted" to the work surface
and that the proper welding pro­cedures are being used.

1. The current sensor may be
faulty.

2. The control PC board may be
faulty.

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F-8 F-8

INVERTEC STT

TROUBLESHOOTING & REPAIR

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

1-888-935-3877

.

PROBLEMS
(SYMPTOMS)

POSSIBLE AREAS OF
MISADJUSTMENT(S)

RECOMMENDED
COURSE OF ACTION

OUTPUT PROBLEMS

Machine loses output while weld­ing. The thermal indicator light is
lit. Normal welding output returns
after about 10 minutes.

1. Check to make sure the fan is
running and operating correctly.

2. Welding application may
exceed recommended duty
cycle.

3. Dirt and dust may have clogged
the cooling channels. Blow out
the unit with clean, dry com­pressed air.

4. Air intake and exhaust louvers
may be blocked due to inade­quate clearance around the
machine.

1. The IGBT heat sink thermostat
or fan thermostat may be defec-

tive. Check or replace.

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TROUBLESHOOTING & REPAIR

F-9 F-9

INVERTEC STT

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

1-888-935-3877

.

PROBLEMS
(SYMPTOMS)

POSSIBLE AREAS OF
MISADJUSTMENT(S)

RECOMMENDED
COURSE OF ACTION

WELDING PROBLEMS

Porosity in the weld. 1. Make sure the gas type and

flow rate is correct for the pro­cedure being used. Shield the
work from excessive outside air
currents.

2. Check the gun and nozzle for
leaks or obstructions.

3. Make certain the machine and
wire feed settings are correct for
the process.

1. Contact the Lincoln Electric
Service Department.

1-888-935-

3877

.

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TROUBLESHOOTING & REPAIR

F-10 F-10

INVERTEC STT

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

1-888-935-3877

.

PROBLEMS
(SYMPTOMS)

POSSIBLE AREAS OF
MISADJUSTMENT(S)

RECOMMENDED
COURSE OF ACTION

WELDING PROBLEMS

Weld bead appears "cold." 1. One or more of the machine

settings may be wrong. Check
the Background, Peak Current,
Tailout (STT II Only), and Wire
Speed controls for proper set­tings. Adjust for optimum weld­ing performance.

2. Make sure the Wire Type and
Wire Size switches are in the
correct position for the elec­trode wire being used.

1. Check for the correct open cir­cuit voltage (approximately
85VDC). If the correct open cir­cuit voltage IS present, the
Background control (R12) or
the Peak Current (R11) and
associated wiring may be faulty.
See the Wiring Diagram. The
control PC board may be faulty.
Also check for loose or faulty
connections on the heavy cur­rent carrying conductors (i.e.,
main transformer, choke, output
diodes, IGBT module and out­put terminals).

2. If the correct open circuit volt­age is NOT present, perform
the Switch Board Test.

3. The output diodes may be
faulty. Check or replace if nec­essary.

4. The driver PC board and or
control PC board may be faulty.

5. The IGBT module may be
faulty. Check or replace.

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TROUBLESHOOTING & REPAIR

F-11 F-11

INVERTEC STT

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

1-888-935-3877

.

PROBLEMS
(SYMPTOMS)

POSSIBLE AREAS OF
MISADJUSTMENT(S)

RECOMMENDED
COURSE OF ACTION

WELDING PROBLEMS

Molten weld puddle appears exces­sively "violent."

1. The Wire Type switch may be in
the wrong position for the elec­trode wire being used.

2. The Peak Current or Back­ground Setting may be too high.
Adjust for optimum welding per­formance.

3. The Tailout may not be set cor­rectly for the process. (STT II
Only)

1. The IGBT module may be faulty.
Check or replace.

2. The IGBT driver PC board may
be faulty.

3. The control PC board may be
faulty.

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TROUBLESHOOTING & REPAIR

F-12 F-12

INVERTEC STT

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

1-888-935-3877.

PROBLEMS
(SYMPTOMS)

POSSIBLE AREAS OF
MISADJUSTMENT(S)

RECOMMENDED
COURSE OF ACTION

WELDING PROBLEMS

Excessive weld spatter. Arc sounds and looks like a standard MIG process.

1. Check the Arc Sense leads for
loose or faulty connections.

2. Make sure the Arc Sense
"WORK" lead is as close as
possible to the welding arc.

3. Make sure the machine and
wire feed settings are correct for
the process and wire being
used.

1. The IGBT module may be faulty.
Check or replace.

2. The IGBT driver PC board may
be faulty.

3. The control PC board may be
faulty.

Poor welding, weld settings drift, or output power is low.

1. Make sure the machine settings
are correct for the welding
process being used.

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

3. Make sure the reconnect switch
S7 is in the correct position for
the three-phase input voltage
being applied.

Do not switch reconnect switch with
input power applied to machine.

1. The current sensor may be
faulty. Check associated leads
for loose or faulty connections.

2. The control PC board may be
faulty.

CAUTION

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TROUBLESHOOTING & REPAIR

F-13 F-13

INVERTEC STT

T1 AUXILIARY TRANSFORMER 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

1-888-935-3877

TEST DESCRIPTION

This test will determine if the correct voltages are being:

a. applied to the primary of the T1 auxiliary transformer.

b. induced upon the secondary windings of the T1 auxiliary transformer.

MATERIALS NEEDED

Volt/Ohmmeter (Multimeter)
Invertec STT wiring diagrams
5/16" Nut driver
3/8" Wrench
Slot head screw driver

Note: Component locations and disassembly procedures may

vary slightly on STT II models

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TROUBLESHOOTING & REPAIR

F-14 F-14

INVERTEC STT

T1 AUXILIARY
TRANSFORMER

PLUG

J31

PLUG

J30

FIGURE F.1 – T1 AUXILIARY TRANSFORMER AND J30/J31 LOCATION

T1 AUXILIARY TRANSFORMER TEST (continued)

TEST PROCEDURE

1. Turn off Invertec STT and disconnect main
AC input power to the machine.

2. Using the 5/16" nut driver, remove the case
wraparound cover.

3. Perform the Input Filter Capacitor

Discharge Procedure. See the
Maintenance section.

ELECTRIC SHOCK can kill.

• Before continuing with
the test procedure, per­form the capacitor dis­charge procedure to
avoid electric shock.

4. Locate the T1 auxiliary transformer and sec­ondary lead molex plugs (J30 and J31) on
the left side, just in front of the main trans­former assembly. Check for broken or loose
wires. See Figure F.1.

WARNING

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TROUBLESHOOTING & REPAIR

F-15 F-15

INVERTEC STT

5. Locate the primary lead molex plug (J21)
just behind the reconnect panel assembly on
the right side of the machine. Check for bro­ken or loose wires. See Figure F.2.

6. Disconnect plugs J30 and J31 from the
wiring harness.

ELECTRIC SHOCK can kill.

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

7. Apply the correct input power to the machine
and test for the correct secondary voltages
at plugs J30 and J31. (Make sure the recon­nect panel is configured properly for the
input voltage being applied.) See Table F.1.

T1 AUXILIARY TRANSFORMER TEST (continued)

RECONNECT

PANEL

PLUG J21

LOCATION BEHIND

RECONNECT PANEL

FIGURE F.2 – PRIMARY LEAD PLUG J21 LOCATION

WARNING

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TROUBLESHOOTING & REPAIR

F-16 F-16

INVERTEC STT

8. If the correct secondary voltages are present
(according to Table F.1), the T1 transformer
is functioning properly.

9. If the secondary voltages are missing or
incorrect, the primary voltages must be
checked.

10. Remove input power to the STT machine.

11. Perform the Input Filter Capacitor

Discharge Procedure.

12. Reconnect Plugs J30 & J31.

ELECTRIC SHOCK can kill.

• Before continuing with
the test procedure, per­form the capacitor dis­charge procedure to
avoid electric shock.

13. Gain access to the primary lead plug J21 by
removing the reconnect panel assembly
from the upper support panel using the 3/8"
wrench and slot head screwdriver. This will
allow the reconnect panel assembly to be
moved out of the way. Be careful NOT to
stress the leads connected to the reconnect
panel. See Figure F.2.

14. Before applying input power make certain
the reconnect panel assembly is insulated
and supported for safe operation.

T1 AUXILIARY TRANSFORMER TEST (continued)

TABLE F.1 – T1 AUXILIARY TRANSFORMER VOLTAGES

TEST POINTS

PLUG J30 PINS 1 TO 2

(LEADS 32 TO 33)

PLUG J31 PINS 1 TO 4

(LEADS 501 TO 504)

PLUG J31 PINS 2 TO 3

(LEADS 212 TO 503)

PLUG J31 PINS 2 TO 5

(LEADS 212 TO 43A)

PLUG J21 PINS 1 TO 4

(LEADS H1 TO H2)

PLUG J21 PINS 1 TO 2

(LEADS H1 TO H3)

PLUG J21 PINS 1 TO 3

(LEADS H1 TO H4)

PLUG J21 PINS 1 TO 6
(LEADS H1 TO H5) (H6)

NORMAL VOLTAGE

115VAC

18VAC

24VAC

42VAC

200/208VAC

220/230VAC

380/415VAC

440/460VAC

WARNING

NOTE: If the main AC input supply voltage varies, the auxiliary transformer voltages will vary by

the same percentages.

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TROUBLESHOOTING & REPAIR

F-17 F-17

INVERTEC STT

ELECTRIC SHOCK can kill.

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

15. Apply the correct input power and carefully
test for the correct primary voltages at plug
J21. See Table F.1.

16. If the correct AC input voltages are applied
to the primary windings and any or all of the
secondary voltages are missing or not cor­rect, the T1 auxiliary transformer may be
faulty.

17. After all tests are complete, reconnect plugs
J30 and J31.

18. Install the case wraparound cover.

T1 AUXILIARY TRANSFORMER TEST (continued)

WARNING

NOTES

F-18 F-18

INVERTEC STT

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T4 AUXILIARY TRANSFORMER TEST

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

1-888-935-3877

.

TEST DESCRIPTION

This test will determine if the correct voltages are being:

a. applied to the primary of the T4 auxiliary transformer.
b. induced on the secondary windings of the T4 auxiliary transformer.

MATERIALS NEEDED

Volt/Ohmmeter (Multimeter)
Invertec STT Wiring Diagrams
Isolated 115VAC supply
5/16" Nut driver
7/16" Wrench

TROUBLESHOOTING & REPAIR

F-19 F-19

INVERTEC STT

WARNING

Note: Component locations and disassembly procedures may

vary slightly on STT II models

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TROUBLESHOOTING & REPAIR

F-20 F-20

INVERTEC STT

T4 AUXILIARY TRANSFORMER TEST (continued)

FIGURE F.3 – OUTPUT CHOKE/IGBT MODULE SPLICED CONNECTION

LOWER

TRAY

AREA

OUTPUT CHOKE/
DARLINGTON MODULE
SPLICED CONNECTION

TEST PROCEDURE

1. Turn off the Invertec STT and disconnect
main AC input power to the machine.

2. Using the 5/16" nut driver, remove the case
wraparound cover.

3. Perform the Input Filter Capacitor

Discharge Procedure. See the
Maintenance section.

ELECTRIC SHOCK can kill.

• Before continuing with
the test procedure, per­form the capacitor dis­charge procedure to
avoid electric shock.

4. Locate the lead connection splice from the
output choke to the IGBT module. Remove
the insulating sleeve. Cut any necessary
cable ties. Using the 7/16" wrench, discon­nect the lead splice. Thread the lower lead
down into the lower tray assembly area.
See Figure F.3.

WARNING

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TROUBLESHOOTING & REPAIR

F-21 F-21

INVERTEC STT

T4 AUXILIARY TRANSFORMER TEST (continued)

5. Disconnect the current sensing Plug J1 from
the control PC board. Carefully remove Plug
J1 and associated leads from control board
compartment. See Figure F.4.

FIGURE F.4 – PLUG J1 LOCATION

LOWER

TRAY
AREA

OUTPUT CHOKE/
DARLINGTON MODULE
SPLICED CONNECTION

J1 CURRENT
SENSING PLUG

6. Locate and disconnect plug J22 from the
wiring harness. See Figure F.5.

FIGURE F.5 – PLUG J22 LOCATION

PLUG J22

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TROUBLESHOOTING & REPAIR

F-22 F-22

INVERTEC STT

T4 AUXILIARY TRANSFORMER TEST (continued)

7. Carefully lift and tilt the Invertec STT
machine onto its right side. See Figure F.6.

8. Using the 7/16" wrench, remove the five
bolts holding the lower tray assembly to the
case bottom.

9. Carefully slide out and support the lower tray
assembly for testing purposes.

10. Locate and remove plug J13 from the

IGBT drive board. See Figure F.7.

FIGURE F.6 – STT ON ITS RIGHT SIDE

MOUNTING
BOLTS (5)

FIGURE F.7 – PLUG J13 LOCATION

T4 AUXILIARY
TRANSFORMER

PLUG J13

IGBT

DRIVE BOARD

STT II

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TROUBLESHOOTING & REPAIR

F-23 F-23

INVERTEC STT

T4 AUXILIARY TRANSFORMER TEST (continued)

11. Locate and remove leads #32A, #32B and
#33A, #33B from the T4 transformer tabs.
See Figure F.8.

ELECTRIC SHOCK can kill.

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

12. Carefully apply the 115VAC isolated supply
to the T4 transformer at the #32 and #33
tabs.

FIGURE F.8 – T4 TRANSFORMER LEAD CONNECTIONS

LEADS

32A, 32B, 33A, 33B

T4 AUXILIARY

TRANSFORMER

STT

STT II

T4 AUXILIARY

TRANSFORMER

LEADS

32A, 32B, 33A, 33B

WARNING

13. Check the secondary AC voltages accord­ing to Table F.2.

14. With the correct 115VAC applied to the pri­mary winding (#32 to #33), if any or all of
the secondary voltages are missing or low,
the T4 auxiliary transformer may be faulty.
Replace the T4 auxiliary transformer.

15. After all tests are completed, reconnect the
following:

Leads #32A, #32B, #33A, #33B to the
T4 transformer tabs

Plug J13 to the IGBT drive board

Plug J22 to the wiring harness

Reinstall lower tray assembly using
7/16” wrench and 5 bolts

Plug J1 to the control PC board

Reconnect lead splice from the output
choke to the IGBT module. Reposition
insulating sleeve.

16. Install the case wraparound cover.

TROUBLESHOOTING & REPAIR

F-24 F-24

INVERTEC STT

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TABLE F.2 – T4 AUXILIARY TRANSFORMER VOLTAGES

TEST POINTS

PLUG J13 PINS 5 TO 6

PLUG J13 PINS 2 TO 3

PLUG J22 PINS 1 TO 2

(LEADS 240 TO 241)

PLUG J22 PINS 2 TO 9

(LEADS 241 TO 242)

PLUG J22 PINS 3 TO 4

(LEADS 243 TO 244)

PLUG J22 PINS 12 TO 13

(LEADS 245 TO 246)

NORMAL VOLTAGES

6VAC

10VAC

18VAC

18VAC

18VAC

18VAC

T4 AUXILIARY TRANSFORMER TEST (continued)

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INPUT RECTIFIER TEST

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

1-888-935-3877

.

TEST DESCRIPTION

This test will help determine if the input rectifier and associated components are functioning
properly.

MATERIALS NEEDED

5/16" Nut driver
Analog Voltmeter/ohmmeter (Multimeter)
Inverter STT Wiring Diagrams

TROUBLESHOOTING & REPAIR

F-25 F-25

INVERTEC STT

WARNING

Note: Component locations and disassembly procedures may

vary slightly on STT II models

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TROUBLESHOOTING & REPAIR

F-26 F-26

INVERTEC STT

INPUT RECTIFIER TEST (continued)

FIGURE F.9 - INPUT RECTIFIER LOCATION

INPUT
RECTIFIER

CA

9

12

B

TEST PROCEDURE

1. Turn off the Invertec STT and disconnect
main AC input power to the machine.

2. Using the 5/16" nut driver, remove the case
wraparound cover.

3. Perform the Input Filter Capacitor

Discharge procedure. See the
Maintenance section.

ELECTRIC SHOCK can kill.

• Before continuing with
the test procedure, per­form the capacitor dis­charge procedure to
avoid electric shock.

4. Locate the input rectifier. See Figure F.9.

5. Locate the leads needed to perform the
tests. See Figure F.9.

6. Use an ANALOG ohmmeter to perform the
tests shown in Table F.3.

WARNING

6. Replace the input rectifier when any of the
tests are NOT OK.

NOTE: When installing a new input rectifier,
torque the mounting nuts (in a cross-tightening
pattern) to 6 inch-pounds (.7 Nm). Torque ter­minals to 26 inch-pounds (3 Nm). PROCEED
TO STEP 7 TO CHECK RELATED COMPO­NENTS.

7. Inspect main power switch S1 and replace
if faulty. Go to step 8.

8. Test capacitors C1 and C2 and replace both
capacitors if either is faulty.

NOTE: Faulty capacitors could be the reason
for input rectifier failure.

Visually inspect the capacitors for leakage,
damage, etc., and use appropriate test equip­ment to determine component integrity.

9. Perform the Switch Board Test.

10. After all tests are completed, install the
case wraparound cover.

TROUBLESHOOTING & REPAIR

F-27 F-27

INVERTEC STT

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INPUT RECTIFIER TEST (continued)

TABLE F.3 – INPUT RECTIFIER TEST

TEST POINTS

+PROBE -PROBE ACCEPTABLE METER READING

9AGreater than 100K ohms
9BGreater than 100K ohms
9CGreater than 100K ohms

A9 Less than 100 ohms
B9 Less than 100 ohms

C9 Less than 100 ohms

12 A Less than 100 ohms
12 B Less than 100 ohms
12 C Less than 100 ohms

A12Greater than 100K ohms
B12Greater than 100K ohms

C12Greater than 100K ohms

NOTES

F-28 F-28

INVERTEC STT

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CAPACITOR BALANCE TEST

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

1-888-935-3877

.

TEST DESCRIPTION

This test will help determine if the capacitors, bleeder resistors and switch boards are func­tioning properly.

MATERIALS NEEDED

5/16" Nut driver
Analog Volt/ohmmeter (Multimeter)

TROUBLESHOOTING & REPAIR

F-29 F-29

INVERTEC STT

WARNING

Note: Component locations and disassembly procedures may

vary slightly on STT II models

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TROUBLESHOOTING & REPAIR

F-30 F-30

INVERTEC STT

CAPACITOR BALANCE TEST (continued)

FIGURE F.10 – SWITCH BOARD TEST POINTS

L8441

L8441

SWITCH

SWITCH

9

9

12

12

TEST PROCEDURE

1. Turn off the Invertec STT and disconnect
main AC input power to the machine.

2. Using the 5/16" nut driver, remove the
case wraparound cover.

ELECTRIC SHOCK can kill.

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

3. Carefully apply the correct input power to
the machine.

NOTE: This test should only be conducted
when the machine reconnect switch and
jumper are set for high voltage (above
380VAC) and the proper line voltage is applied.

4. Test for VDC across terminals #9 and #12 of
one switch board and repeat the test for the
other switch board. See Table F.4 in this
procedure for expected voltage readings.
See Figure F.10.

A. If less than 25VDC difference is mea-

sured between each switch board, the
capacitive balance is OK. This indi­cates that capacitors C1, C2, and resis­tors R1 and R9 are functioning proper­ly. Proceed to Step #5.

B. If more than 25VDC difference is mea-

sured between each switch board, test
each of the following components:
Capacitors C1, C2 and resistors R1
and R9. See the Invertec STT Wiring
Diagram.

WARNING

5. Adjust the Peak and Background controls to
the minimum settings (controls on case
front).

6. Jumper together pins "C" and "D" on the 14

pin amphenol. This will energize the output
terminals.

7. Test for VDC across terminals #9 and #12 of

one switch board and repeat the test for the
other switch board. See Table F.4 in this
procedure for expected voltage readings.
See Figure F.10.

A. If less than 15VDC difference is mea-

sured between each switch board, the
test is OK.

B. If more than 15VDC difference is mea-

sured between each switch board, the
switch board(s) and or power PC board
may be faulty. Perform the Switch

Board Test. Perform the Power Board
Test.

8. After all tests are completed, remove the
jumper between pins C and D on the 14-pin
amphenol.

9. Install the case wraparound cover.

TROUBLESHOOTING & REPAIR

F-31 F-31

INVERTEC STT

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CAPACITOR BALANCE TEST (continued)

TABLE F.4 – EXPECTED VOLTAGE READINGS

If VAC Input is:

460 VAC
440 VAC
415 VAC

380 VAC

VDC at terminals #9 (+) and #12 (-)

should be approximately:

325VDC
311VDC
293VDC
269VDC

NOTES

F-32 F-32

INVERTEC STT

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SWITCH BOARD TEST

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

1-888-935-3877

.

TEST DESCRIPTION

The Switch Board Test determines if the switch boards are operating properly. This resistance
test is preferable to a voltage test with the machine energized because these boards can be
damaged easily. In addition, it is dangerous to work on these boards with machine power ON.

MATERIALS NEEDED

Analog Volt/ohmmeter (Multimeter)
5/16" Nut driver

TROUBLESHOOTING & REPAIR

F-33 F-33

INVERTEC STT

WARNING

Note: Component locations and disassembly procedures may

vary slightly on STT II models

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TROUBLESHOOTING & REPAIR

F-34 F-34

INVERTEC STT

SWITCH BOARD TEST (continued)

FIGURE F.11 - SWITCH BOARD RESISTANCE TEST

TEST PROCEDURE

NOTE: There are two switch boards. One is

located on each side of the machine.
NOTE: The switch boards are designed to

receive gate (turn-on) signals from the driver
board (pulse transformer secondaries). The
internal board circuitry processes the signals and
outputs them to the FETs. The switch board cir­cuitry contains snubber circuitry to protect the
FETs. This protection is supplemented by off­board resistors. The switch board design accom­modates the connection point(s) for the capaci­tor(s), main transformer primary windings, input
rectifier, and reconnect switches.

1. Turn off Invertec STT and disconnect main
AC input power to the machine.

2. Using the 5/16" nut driver, remove the case
wraparound cover.

3. Perform the Input Filter Capacitor

Discharge Procedure. See the
Maintenance section.

ELECTRIC SHOCK can kill.

• Before continuing with the
test procedure, perform
the capacitor discharge
procedure to avoid electric
shock.

4. Disconnect all wiring harness leads
(401/403, 1/8, 9, 12, 4/5, 402/404) from the
switch board.

5. Fold the leads up so they do not interfere with

the exposed terminals. See Figure F.11.

6. Using an analog ohmmeter, perform the resis-

tance tests detailed in Table F.5 and shown in
Figure F.11. If any test fails, replace both
switch boards. See the Switch Board
Removal and Replacement procedure.

7. If the switch boards appear to be burned or

overheated, or if the machine was supplied by
a 380 VAC or higher voltage supply when the
failure occurred, replace the capacitors and
the switch boards.

WARNING

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TROUBLESHOOTING & REPAIR

F-35 F-35

INVERTEC STT

SWITCH BOARD TEST (continued)

Apply Positive Apply Negative
Test Probe to Test Probe to
Terminal Terminal Test Result Conclusion Repair Action Next Procedure Notes

1/8 12 Greater than OK None Continue

1K ohm

Less than Shorted Replace both Snubber Test
100 ohms switch boards

12 1/8 Less than OK None Continue

100 ohms

Greater than Open Replace both Snubber Test
1K ohm switch boards

9 4/5 Greater than OK None Continue

1K ohm

Less than Shorted Replace both Snubber Test
100 ohms switch boards

4/5 9 Less than OK None Continue

100 ohms

Greater than Open Replace both Snubber Test
1K ohm switch boards

1/8 9 Less than OK None Continue

100 ohms

Greater than Open Replace both Snubber Test
1K ohm switch boards

9 1/8 Greater than OK None Continue

1K ohm

Less than Shorted Replace both Snubber Test
100 ohms switch boards

12 4/5 Less than OK None Continue

100 ohms

Greater than Open Replace both Snubber Test
1K ohm switch boards

4/5 12 Greater than OK None Continue

1K ohm

Less than Shorted Replace both Snubber Test
100 ohms switch boards

Continued . . .

NOTE: K ohm = ohm reading multiplied by 1000.
NOTE: Always make sure that switch boards are changed in matched pairs. Never mix an old style (different

part number) switch board with a new switch board (new part number).

TABLE F.5 – SWITCH BOARD RESISTANCE TEST

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TROUBLESHOOTING & REPAIR

F-36 F-36

INVERTEC STT

Apply Positive Apply Negative
Test Probe to Test Probe to
Terminal Terminal Test Result Conclusion Repair Action Next Procedure Notes

12 401/403 Greater than OK None Continue

1K ohm

Less than Shorted Replace both Snubber Test
100 ohms switch boards

401/403 12 Less than OK None Continue

100 ohms

Greater than Open Replace both Snubber Test
1K ohm switch boards

9 402/404 Less than OK None Continue

100 ohms

Greater than Open Replace both Snubber Test
1K ohm switch boards

402/404 9 Greater than OK None Continue

1K ohm

Less than Shorted Replace both Snubber Test
100 ohms switch boards

SWITCH BOARD TEST (continued)

NOTE: K ohm = ohm reading multiplied by 1000.
NOTE: Always make sure that switch boards are changed in matched pairs. Never mix an old style (different

part number) switch board with a new switch board (new part number).

TABLE F.5 – SWITCH BOARD RESISTANCE TEST (continued)

8. Reconnect all wiring harness leads (401/403,
1/8, 9, 12, 4/5, 402/404) to the switch board.

9. Install the case wraparound cover.

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SNUBBER RESISTORS TEST

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

1-888-935-3877.

DESCRIPTION

This test will determine if the snubber resistors (R4, R5, R6, R7) are functioning properly.

MATERIALS NEEDED

Analog Volt/ohmmeter (Multimeter)
STT Wiring Diagrams
5/16” Nut driver

TROUBLESHOOTING & REPAIR

F-37 F-37

INVERTEC STT

WARNING

Note: Component locations and disassembly procedures may

vary slightly on STT II models

TROUBLESHOOTING & REPAIR

F-38 F-38

INVERTEC STT

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SNUBBER RESISTORS TEST (continued)

FIGURE F.12 - REMOVING LEADS

TEST PROCEDURE

1. Turn off Invertec STT and disconnect main
AC input power to the machine.

2. Using the 5/16" nut driver, remove the case
wraparound cover.

3. Perform the Input Filter Capacitor

Discharge Procedure. See the
Maintenance section.

ELECTRIC SHOCK can kill.

• Before continuing with the
test procedure, perform
the capacitor discharge
procedure to avoid electric
shock.

4. Locate and gain access to the switch board.

5. Remove leads from terminals 401/403,
402/404 on the switch board. See Figure
F.12.

WARNING

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TROUBLESHOOTING & REPAIR

F-39 F-39

INVERTEC STT

SNUBBER RESISTORS TEST (continued)

FIGURE F.13 - SWITCH BOARD TEST POINTS

6. Test for 25 ohms resistance from lead termi­nal 401 to terminal 12 on the switch board.
See Figure F.13.

a. If 25 ohms is measured, resistor R4 is OK.

b. If 30 ohms or more is measured, resistor

R4 is faulty and must be replaced.

c. If 20 ohms or less is measured, resistor

R4 is faulty and must be replaced.

7. Repeat the same procedures to test R5, R6,
and R7 according to Table F.6.

8. Reconnect leads 401/403 and 402/404 to the
switch board.

9. Install the case wraparound cover.

L8441 L8441 SWITCHSWITCH

401401/403 1212

9

12402/404

Check Test Result Conclusion Next Test Step Repair Action

Lead 401 to 25 ohms OK Continue
Terminal 12 >30 ohms R4 open Replace R4

<20 ohms R4 faulty

Lead 402 to 25 ohms OK Continue
Terminal 9 >30 ohms R5 open Replace R5

<20 ohms R5 faulty

Lead 403 to 25 ohms OK Continue
Terminal 12 >30 ohms R6 open Replace R6

<20 ohms R6 faulty

Lead 404 to 25 ohms OK Continue
Terminal 9 >30 ohms R7 open Replace R7

<20 ohms R7 faulty

> = GREATER THAN < = LESS THAN

TABLE F.6 – SNUBBER RESISTORS TEST

NOTES

F-40 F-40

INVERTEC STT

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POWER BOARD TEST

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

1-888-935-3877

.

TEST DESCRIPTION

This test will help determine if the power PC board is receiving the correct AC voltages and
also if the correct DC voltages are being generated on the power PC board.

MATERIALS NEEDED

5/16" Nut driver
Volt/ohmmeter (Multimeter)
Wiring diagram

TROUBLESHOOTING & REPAIR

F-41 F-41

INVERTEC STT

WARNING

Note: Component locations and disassembly procedures may

vary slightly on STT II models

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TROUBLESHOOTING & REPAIR

F-42 F-42

INVERTEC STT

POWER BOARD TEST (continued)

FIGURE F.14 – REMOVING THE FRONT PANEL ASSEMBLY

POWER
PC BOARD

(Located
on Back of
Case Front)

QUICK CHECK PROCEDURE

1. Turn off the Invertec STT and disconnect
main AC input power to the machine.

2. Using the 5/16" nut driver, remove the case
wraparound cover.

3. Locate relays CR1 and CR2 just to the front of
the fan motor.

ELECTRIC SHOCK can kill.

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

4. Apply the correct input power and turn ON the
Invertec STT machine.

5. After about a 5 second delay the relays
should activate. This can be determined by
an audible click which can be heard when the
relays are activated. If the relays are being
activated, the power PC board is most likely

OK. If the relays are NOT being activated, the
power PC board could be faulty. Continue
with the voltage tests.

VOLTAGE TEST PROCEDURE

1. Remove input power to the Invertec STT.

2.

Perform the Input Filter Capacitor Discharge
Procedure. See the Maintenance section.

ELECTRIC SHOCK can kill.

• Before continuing with the
test procedure, perform
the capacitor discharge
procedure to avoid electric
shock.

3. Using the 5/16" nut driver, loosen the front
control panel by removing the four sheet
metal screws from the top and bottom of the
front panel. Carefully move the front panel
assembly to the right to gain access to the
power PC board. See Figure F.14.

WARNING

WARNING

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TROUBLESHOOTING & REPAIR

F-43 F-43

INVERTEC STT

POWER BOARD TEST (continued)

FIGURE F.15 – POWER PC BOARD TEST POINTS

POWER BOARD

J6

J7

J14

L8033

501

504

302

275

211A

305

311

313

309

310

301

212A

4. Secure and insulate the front panel assembly
for POWER ON testing.

ELECTRIC SHOCK can kill.

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

5. Apply the correct input power and turn ON the
machine.

6. Carefully test for 18VAC input from the T1
Auxiliary Transformer between plug J7 pin 5
(lead#501) and plug J7 pin 6 (lead #504) at
the power PC board. See Figure F. 15.

NOTE: If the 18VAC is NOT present, perform
the T1 Auxiliary Transformer Test. Also check
associated wiring. See the Wiring Diagram.

WARNING

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TROUBLESHOOTING & REPAIR

F-44 F-44

INVERTEC STT

POWER BOARD TEST (continued)

FIGURE F.16 – SIMPLIFIED TRIGGER CIRCUIT

FROM PROTECTION
BOARD OVERVOLTAGE

PWM

OUTPUTS

TO POWER

BOARD

7J6

2J6

11J4

3J4

13J36

5J36

8J33

6J34

9J4

12J4

3J31

6J22

6J4

POWER BOARD CONTROL BOARD

REMOTE

PROTECTION

BOARD

14 AMPHENOL

#301

#305

#503A

#224

#210

#212

#223

#212C

#413

#405

C

D

T1 AUXILIARY

TRANSFORMER

2
4

V
A
C

P

W

M

5J4

TO
POWER
BOARD

2J31

3.5 ohms

3.5 ohms

STT II Only

#379

7. Carefully test for 15VDC output from the
power PC board at plug J6 pin1 (lead #275)
(-) and plug J6 pin 6 (lead #302)(+). See

Figure F.15.

NOTE: If the 18VAC is present but the 15VDC is
NOT, the power PC board may be faulty.

8. Carefully test for 24VAC input from the T1
Auxiliary Transformer between plug J6 pin 4
(lead#211A) and plug J6 pin 9 (lead#212A).
See Figure F.15.

NOTE: If the 24VAC is NOT present, perform the
T1 Auxiliary Transformer Test. Also check the
associated wiring. See the Wiring Diagram. The
control PC board or thermostats may be faulty.
See Figure F.16, the Simplified Trigger Circuit
diagram.

9. Carefully test for 24VDC at the power PC
board at plug J7 pin 2 (lead #309)(+) to plug
J14 pin2 (lead #313)(-). See Figure F.15.

NOTE: If the 24VAC is present but the 24VDC is
NOT, the power PC board may be faulty.

10. Carefully test for approximately 24VDC at
plug J7 pin 2 (lead#309)(+) to plug J7 pin 4
(lead#310)(-). If the 24VDC is NOT present,
test for approximately 1VDC at plug J14 pin1
(lead#311)(+) to plug J14 pin 2 (lead#313)(-).
See Figure F.15.

NOTE: If more than 1VDC is measured, perform
the Protection Board Test.

NOTE: If approximately 1VDC IS present and
the 24VDC is NOT present at leads #309 to
#310, the power PC board may be faulty.

11. After all tests are completed, install the front

panel assembly.

12. Install the case wraparound cover.

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PROTECTION BOARD TEST

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

1-888-935-3877

.

TEST DESCRIPTION

This test will help determine if the protection PC board is functioning properly.

MATERIALS NEEDED

5/16" Nut driver
Volt/ohmmeter (Multimeter)
Wiring Diagrams

TROUBLESHOOTING & REPAIR

F-45 F-45

INVERTEC STT

WARNING

Note: Component locations and disassembly procedures may

vary slightly on STT II models

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TROUBLESHOOTING & REPAIR

F-46 F-46

INVERTEC STT

PROTECTION BOARD TEST (continued)

FIGURE F.17 – PROTECTION PC BOARD TEST POINTS

PROTECTION

L7915-[ ]

313

311

J8

J15

315

317

314

316

TEST PROCEDURE

1. Turn off the Invertec STT and disconnect
main AC input power to the machine.

2. Using the 5/16" nut driver, remove the case
wraparound cover.

3.

Perform the Input Filter Capacitor Discharge
Procedure. See the Maintenance section.

ELECTRIC SHOCK can kill.

• Before continuing with
the test procedure, per­form the capacitor dis­charge procedure to
avoid electric shock.

4. Locate the protection PC board just in front
of the input rectifier and relay mountings.

ELECTRIC SHOCK can kill.

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

5. Apply the correct input power and turn the
machine ON.

6. Test for approximately 1VDC from plug J8
pin 1 (lead #311)(+) to plug J8 pin 3 (lead
#313) (-). See Figure F.17.

A. If approximately 1VDC is present, the

protection PC board is functioning prop­erly.

B. If more than 5 VDC is measured, per-

form the Capacitor Balance Test.

WARNING

WARNING

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TROUBLESHOOTING & REPAIR

F-47 F-47

INVERTEC STT

FIGURE F.18 - LEADS #309, #309A AT CR1, CR2 RELAYS

CR2

CR1

309A

309

PROTECTION BOARD TEST (continued)

7. If the Capacitor Balance Test is OK and

more than 5VDC is present at leads #311 to
#313 (Step 6), the protection PC board may
be faulty.

NOTE: The above voltage checks pertain only
to the over voltage signal from the protection
PC board to the power PC board. The capaci­tor precharge circuits are also incorporated
within the protection PC board. If the problem
has not been identified, carefully proceed with
the following steps.

8. Remove input power to the Invertec STT
machine.

9.

Perform the Input Filter Capacitor Discharge
Procedure. See the Maintenance section.

ELECTRIC SHOCK can kill.

• Before continuing with
the test procedure, per­form the capacitor dis­charge procedure to
avoid electric shock.

10. Locate and remove leads #309 and #309A
from CR1 and CR2 relays. See Figure
F.18.

ELECTRIC SHOCK can kill.

•

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

11. Apply correct input power and turn ON the
machine.

12. Check for approximately 12VDC from plug
J15 pin 1 (lead #314)(+) to plug J15 pin 4
(lead#315) (-). See Figure F.17.

13. Check for approximately 12VDC from plug
J15 pin 3 (lead #316)(+) to plug J15 pin 6
(lead#317) (-). See Figure F.17.

14. If a low voltage is present in either steps 12
or 13 (approximately 1VDC), perform the

Capacitor Balance Test.

15. If the Capacitor Balance Test is OK, the
protection PC board may be faulty.

16. Be certain to replace leads #309 and #309A
onto the CR1 and CR2 relays.

17. After all tests are completed, install the
case wraparound cover.

WARNING

WARNING

NOTES

F-48 F-48

INVERTEC STT

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TRIGGER CIRCUIT TEST

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

1-888-935-3877

.

TEST DESCRIPTION

This test includes a few quick checks to troubleshoot the machine trigger circuit. The
Simplified Trigger Circuit Diagram will enable the technician to view the trigger circuit in an
abbreviated, uncomplicated format.

MATERIALS NEEDED

5/16" Nut driver
Volt/ohmmeter (Multimeter)
Wiring Diagram and board Schematics

TROUBLESHOOTING & REPAIR

F-49 F-49

INVERTEC STT

WARNING

Note: Component locations and disassembly procedures may

vary slightly on STT II models

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TROUBLESHOOTING & REPAIR

F-50 F-50

INVERTEC STT

TRIGGER CIRCUIT TEST (continued)

FIGURE F.19 – PLUG J31 LOCATION

PLUG

J31

TEST PROCEDURE

1. Turn off the Invertec STT and disconnect main
AC input power to the machine.

2. Using the 5/16" nut driver, remove the case
wraparound cover.

3. Perform the Input Filter Capacitor
Discharge Procedure. See the Maintenance
section.

ELECTRIC SHOCK can kill.

• Before continuing with the
test procedure, perform
the capacitor discharge
procedure to avoid electric
shock.

4. Locate plug J31 at the left side of the
machine. See Figure F.19.

WARNING

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TROUBLESHOOTING & REPAIR

F-51 F-51

INVERTEC STT

TRIGGER CIRCUIT TEST (continued)

FIGURE F.20 – 14 PIN AMPHENOL AND PLUG J31 PIN ASSIGNMENTS

K

B

I

H

N

L

C

D

M

G

E

F

J

A

5. Using the ohmmeter check for approximately

3.5 ohms resistance from pin "D" of the 14 pin
amphenol to plug J31 pin 2 (lead #212). See
Figure F.20, and Figure F.22, Simplified

Trigger Circuit Diagram.

FIGURE F.21 – CONTROL PC BOARD MOLEX PLUG

J4

223

210

G2782-[ ]

STT CONTROL

J1

J3J2

J28J27

J17

J5

6. Using the ohmmeter, check for approximately

3.5 ohms resistance from pin "C" of the 14 pin
amphenol (see Figure F.20) to plug J4 pin 9

(lead#223) at the control PC board. See
Figure F.21 and Figure F.22, Simplified

Trigger Circuit Diagram.

PLUG J31

212

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TROUBLESHOOTING & REPAIR

F-52 F-52

INVERTEC STT

TRIGGER CIRCUIT TEST (continued)

FIGURE F.22 – SIMPLIFIED TRIGGER CIRCUIT DIAGRAM

FROM PROTECTION
BOARD OVERVOLTAGE

PWM

OUTPUTS

TO POWER

BOARD

7J6

2J6

11J4

3J4

13J36

5J36

8J33

6J34

9J4

12J4

3J31

6J22

6J4

POWER BOARD CONTROL BOARD

REMOTE

PROTECTION

BOARD

14 AMPHENOL

#301

#305

#503A

#224

#210

#212

#223

#212C

#413

#405

C

D

T1 AUXILIARY

TRANSFORMER

2
4

V
A
C

P

W

M

5J4

TO

POWER

BOARD

2J31

3.5 ohms

3.5 ohms

STT II Only

#379

7. Using the ohmmeter check for continuity (zero
ohms) from plug J31 pin 3 (lead#503A) to plug
J4 pin 6 (lead#210). See Figure F.22,
Simplified Trigger Circuit Diagram.

8. If any of the resistance checks are abnormal­ly high in steps 5, 6 or 7, check for broken or
loose wires, connections or "open" ther­mostats. Also check the small inductors on
the Remote Protection Board. See Figure
F.22, Simplified Trigger Circuit Diagram.

ELECTRIC SHOCK can kill.

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

9. Apply the correct input power to the machine
and turn ON.

10. Locate plug J6 on the power PC board. See

Figure F. 15. in the Power Board Test.

11. Carefully check for approximately 1VDC from
plug J6 pin 2 (lead #305)(+) to plug J6 pin 7
(lead #301) (-). If the approximately 1VDC is
present the power PC board and protection
PC board are functioning properly for the trig­ger circuit to operate. If the correct DC volt­age is NOT present, perform the Protection
Board Test and the Power Board Test.

12. Test to make sure the T1 auxiliary trans-

former is producing 24VAC. See Figure F.22,
Simplified Trigger Circuit Diagram.

13. If the above tests do not reveal the problem,

the control PC board or associated wiring
may be faulty. See Figure F.22, Simplified
Trigger Circuit Diagram.

WARNING

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IGBT MODULE

REMOVAL AND REPLACEMENT

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

1-888-935-3877

.

DESCRIPTION

The following procedure will aid the technician in the removal and replacement of the IGBT
module located in the lower tray assembly.

MATERIALS NEEDED

5/16" Nut driver
Phillips head screw driver
7/16" wrench
Needle nose pliers
1/2" Wrench
12mm Wrench
3/16" Allen type wrench
Dow Corning 340 Heat Sink Compound (Lincoln E1868).
Silicone Rubber RTV Coating (Lincoln E2861 or Dow 3140)

TROUBLESHOOTING & REPAIR

F-53 F-53

INVERTEC STT

WARNING

Note: Component locations and disassembly procedures may

vary slightly on STT II models

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TROUBLESHOOTING & REPAIR

F-54 F-54

INVERTEC STT

IGBT MODULE REMOVAL

AND REPLACEMENT (continued)

FIGURE F.23 – OUTPUT CHOKE LEAD DISCONNECTION

LOWER

TRAY

AREA

OUTPUT CHOKE/
IGBT MODULE
SPLICED CONNECTION

PROCEDURE

1. Turn off the Invertec STT and disconnect main
AC input power to the machine.

2. Using the 5/16" nut driver, remove the case
wraparound cover.

3. Perform the Input Filter Capacitor
Discharge Procedure. See the Maintenance
section.

ELECTRIC SHOCK can kill.

• Before continuing with the
test procedure, perform
the capacitor discharge
procedure to avoid electric
shock.

4. Locate the lead connection splice from the
output choke to the IGBT module. Remove
the insulating sleeve. Using the 7/16" wrench
disconnect the lead splice. Thread the lower
lead down into the lower tray assembly area.
See Figure F.23.

WARNING

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TROUBLESHOOTING & REPAIR

F-55 F-55

INVERTEC STT

IGBT MODULE REMOVAL

AND REPLACEMENT (continued)

FIGURE F.24 – PLUG J1 DISCONNECTION

LOWER

TRAY

AREA

OUTPUT CHOKE/
IGBT MODULE
SPLICED CONNECTION

J1 CURRENT
SENSING PLUG

5. Disconnect the current sensing plug J1 from
the control PC board. Carefully remove plug

J1 and associated leads from the control PC
board compartment. See Figure F.24.

FIGURE F.25 – PLUG J22 DISCONNECTION

PLUG J22

6. Locate and disconnect plug J22 from the
wiring harness. See Figure F.25.

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TROUBLESHOOTING & REPAIR

F-56 F-56

INVERTEC STT

IGBT MODULE REMOVAL

AND REPLACEMENT (continued)

FIGURE F.26 – STT PLACED ON ITS RIGHT SIDE

MOUNTING
BOLTS (5)

7. Carefully lift and tilt the Invertec STT
machine onto its right side. See Figure F.26.

8. Using the 7/16" wrench, remove the five
bolts holding the lower tray assembly to the
case bottom.

9. Carefully slide out and support the lower tray
assembly.

10. Using the needle nose pliers, remove the
strain relief holding the J22 lead harness to
the case bottom.

11. Using the 1/2" wrench, remove the IGBT
cable from the negative output terminal.

12. Carefully remove the lower tray assembly
clear from the machine.

13. Remove the rubber RTV coating from the
IGBT module.

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TROUBLESHOOTING & REPAIR

F-57 F-57

INVERTEC STT

IGBT MODULE REMOVAL

AND REPLACEMENT (continued)

FIGURE F.27 – IGBT MODULE CONNECTIONS

E

E

IGBT
MODULE

C

G

STT II

For steps 14-18, see Figure F.27.

14. Using the phillips head screw driver, remove
the small leads from the small "E" and "B"
terminals. Note lead placement for reassem­bly.

15. Using the 12mm wrench, remove the large
lead and the #289 lead from the large "E" ter­minal. Note lead placement for reassembly.

16. Using the 12mm wrench, remove the large
lead and the #287 lead from the large "C"
terminal. Note lead placement for reassem­bly.

17. Using the 3/16" Allen type wrench, remove
the four socket head cap screws that mount
the module to the heat sink.

18. Carefully remove the IGBT module.

19. Upon reassembly, use Dow Corning 340
Heat Sink Compound (Lincoln E1868)
between the module and the heat sink.

20. Mount the new module using the socket
head cap screws and torque to 35 inch
pounds.

Note: The torque should be rechecked after

three hours.

21. Using the 12mm wrench, assemble the large
lead and the smaller #289 lead to the large
"E" terminal. Torque to 86 inch pounds.

22. Using the 12mm wrench, assemble the large

lead and the smaller #287 lead to the large
"C" terminal. Torque to 86 inch pounds.

23. Using the phillips head screw driver,
reassemble the small leads to the small "E"
and "G" terminals. Torque to 13 inch
pounds.

24. Apply the Silicone Rubber RTV Coating
(Lincoln E2861 or Dow 3140) to the termi­nals and lead connections as was previously
removed.

25. Replace the lower tray assembly.

26. Connect plug J22 to the wiring harness and
plug J1 to the control PC board.

27. Connect the lead splice between the output
choke and the IGBT module.

28. Install the case wraparound cover.

NOTES

F-58 F-58

INVERTEC STT

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SWITCH BOARD

REPLACEMENT

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

1-888-935-3877

.

DESCRIPTION

This procedure will aid the technician in the removal and replacement of the switch boards.

MATERIALS NEEDED

5/16" Nut driver
7/16" Wrench
3/16" Allen type wrench
3/16" Socket wrench
Dow Corning 340 Heat Sink Compound (Lincoln E1868)
ANALOG Ohmmeter

TROUBLESHOOTING & REPAIR

F-59 F-59

INVERTEC STT

WARNING

Note: Component locations and disassembly procedures may

vary slightly on STT II models

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TROUBLESHOOTING & REPAIR

F-60 F-60

INVERTEC STT

SWITCH BOARD REPLACEMENT (continued)

FIGURE F.28 – SWITCH BOARD REMOVAL

PROCEDURE

NOTE: If a test indicates that a switch board is

defective, both switch boards must be replaced at
the same time. In addition to replacing the switch
boards, replace capacitors C1 and C2 if the fol­lowing conditions exist:

a. The machine was operating from 380 VAC

or higher when the failure occurred.

b. Burned areas are visible on the switch

boards.

1. Turn off the Invertec STT and disconnect main
AC input power to the machine.

2. Using the 5/16" nut driver, remove the case
wraparound cover.

3.

Perform the Input Filter Capacitor Discharge
Procedure. See the Maintenance section.

ELECTRIC SHOCK can kill.

• Before continuing with the
test procedure, perform the
capacitor discharge proce­dure to avoid electric
shock.

4. Carefully disconnect the leads at the top of the
switch board.

5. Using the 3/16" socket wrench, remove the
four cap screws from the switch board. See
Figure F.28.

WARNING

SOCKET
HEAD
SCREWS

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TROUBLESHOOTING & REPAIR

F-61 F-61

INVERTEC STT

SWITCH BOARD REPLACEMENT (continued)

6. Using the 7/16" wrench, remove the two hex
head capacitor screws located in the center
of the switch board. Hold the board firmly as
you remove the screws.

7. Carefully remove the switch board.

8. Clean the heat sink surfaces thoroughly to
remove all the heat sink compound. (During
machine operation, this compound helps
conduct heat from the switch board to the
heat sinks.

9. Apply a thin layer (.002") of Dow Corning
340 Heat Sink Compound (Lincoln E1868) to
the mounting surfaces of the new switch
board and to the capacitor terminals. DO
NOT allow the compound to enter the
mounting screw holes. It can distort the
torque values.

10. Prepare to mount the new switch board on
the heat sink by first lining up the mounting
holes. Then press the switch board into
place.

11. Insert each of the four socket head screws

into the mounting holes. Thread them finger
tight. The threads are soft -- be careful no to
cross-thread them.

12. Insert each of the two hex head screws into
the capacitor terminal holes. Thread them
finger tight. Be careful not to cross-thread the
screws.

13. Torque both sets of screws in 10 inch-pound
increments. Use a diagonal tightening
sequence. Torque the four socket head
screws to 44 inch-pounds (5 Nm). Torque the
two hex head screws to 55 inch-pounds (6
Nm).

Failure to connect the switch board leads correct­ly can result in damage to the Invertec STT
machine when power is applied.

14. Reconnect all the leads to the switch board.
Be sure each lead is connected to the correct
terminal.

15. Perform the Test after Repair of Switch

Boards and/or Capacitors.

NOTE: Always make sure that the switch boards
are changed in matched pairs. Never mix an old
style switch board (different part number) with
new style (new part number).

CAUTION

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TROUBLESHOOTING & REPAIR

F-62 F-62

INVERTEC STT

SWITCH BOARD REPLACEMENT (continued)

TEST AFTER REPAIR OF SWITCH
BOARDS AND/OR CAPACITORS

The following test must be performed after the
switch boards and/or the capacitors have been
replaced.

NOTE: Always make sure that switch boards are
changed in matched pairs. Never mix an old style
(different part number) switch board with a new
style (new part number).

TEST PROCEDURE

1. Turn main power OFF.

2. Perform Input Filter Capacitor Discharge
Procedure. See the Maintenance section.

ELECTRIC SHOCK can kill.

• Before continuing with the
test procedure, perform
the capacitor discharge
procedure to avoid electric
shock.

3. Connect a shorting conductor across termi­nals 14 and 53 of the protection PC board.
See Figure F.29.

4. Set an ANALOG ohmmeter to X1000 range
and place the probes on terminals 9 (+) and
12 (–) of one switch board. The meter will
show the capacitors charging up and may
take a minute or so to stabilize. The final
meter reading should not exceed 8600 ohms
(8.6 on the scale).

5. Test the other switch board the same way.

NOTE: Repeat the Input Filter Capacitor
Discharge Procedure.

6. Remove the shorting conductor set up in step

3.

7. Replace 20 amp fuses with 5-amp fuses in
the input supply fuse holders.

NOTE: These fuses should be installed to pro­tect against excessive current flow caused by a
short circuit during the procedure.

WARNING

FIGURE F.29 — SHORTING TERMINALS 14 AND 53 OF PROTECTION BOARD

L7915-[ ]

PROTECTION

53

14

JUMPER TERMINALS