Sencore FE20 Service Manual

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FE

20

HI-L O

METER

SENCORE SERVICE

3200 SENCORE DRIVE, SIOUX FALLS, SOUTH DAKOTA 57107

M A N U A L

Safety Precautions

When testin g elec t ronic equipment, there is always a danger p rese n t . Un
expecte d high voltages can be present at unusual locatio ns in defective equip
ment. The te c h n ic ia n should become familiar with the de v i ce that he is
working on and ob s erve the following precau t io ns.

1. An is olatio n tr ans f ormer should always be used on equipment having the
chassi s tied to one si de of the AC power line.

2. When making te st lead con n ec tio n s to high voltage points, r e m o ve the
power, if this cannot be done, be su r e to avoid contact with other equip
ment or m e t a l objects. Place one hand in your pocket a s a safe t y p re
caution and stand on an insulated floor to reduce the poss i bilit y of shock.

3. Discha r g e f ilter ca pac i tors be f o re con nec ting test leads to them. Ca
pa cito r s ca n st ore a ch a r ge that could be dangerous to the techni cian .

4. Be su r e your equipment is in good ord e r. Broken or fra y ed tes t leads
can be e xtre mely dangerous and can expose the te c h ni c ia n to dangerous
poten t ia ls.

5. Remove the test lead s im mediate ly a f t er the test has been completed to
reduc e the possibil i t y of shock.

6. Do not work alone when working on hazardous circu its . Always have
another pe r son c l ose by in case of accident . Re member, even a minor
shock can be the c ause of a mo r e seri ous ac c id e n t, such as fallin g a
gains t the equipment, or coming in con ta c t with higher voltages.

TABLE OF CONTENTS PAGE

SAFE TY PRECAUTIONS..................................................................................... 2

DES CRIPTION ....................................................................................................... 4

SP ECIFIC ATION S ................................................................................................ 4

OPE RATION........................................................................................................... 6

Shielded T est Lead and Probe for the HI-LO M eter
Contro ls on the HI-LO Meter

Batter y Install at io n and Testing ........................................................... 7

Measuri ng DC Voltage.............................................................................. 7

Measurin g DCV with a Zero Center Scale......................................... 8

Measurin g DC Curren t............................................................................. 8

Measuri ng AC Voltage............................................................................. 8

Measuri ng R esis t ance (HI POWER O HMS )......................................... 9

Measuri ng Resi s tance (LO POWER OHMS)......................................... 9

Measurin g Res i s tance of Thermistors................................................ 9

Measur in g DC High Voltage................................................................... 10

Measurin g De c ibels (db) .......................................................................... 10

Measu r in g AC Curren t............................................................................. 12

Measuri n g sm all L eak ag e Current....................................................... 13

Overload Prote c t io n..................................................................................... 13

.................................................................. 6

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6

CIRCUIT DESCRIPTIO N ..................................................................

Gen eral........................................................................................................... 14

DC Vol tage.....................................................................................

DC Cur rent.................................................................................................... 14

Resis tan ce (HI POWER)

Resis tan ce (LO PO WE R) .......................................................................... 15

AC Vol tage .................................................................................................... 15

MAINT E N A N CE .................................................................................................... 15

Intro d u c ti o n .................................................................................................... 15

Dis asse mbly Ins t ructi ons.......................................................................... 15

Cali b r a t i o n of the HI-LO M ete r

Building a Me ter Cal ibrator................................................................... 17

Trou b le Chart ................................................................................................ 18

Schematic and P arts Li st (S e p a r a te Sheet)

ILLUSTRATIONS AND CHARTS

Fig. 1 db Corre c t i on Cha rt

Fig. 2 Voltage vs. Power C hart....................................................... 11

Fig. 3 AC Cur r e n t Adapt e r ................................................................... 12

Fig. 4 Measurin g s mall Leakage Curren t s..................................... 13

Fig . 5 P. C. Board Layout...................................................................... 16

Fig. 6 Calib r a t o r fo r HI-LO Met er.................................................... 17

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14

I ISTIOCTIM M1 IML Fll THE SEICII E FE20

H I-L I FIEL I EFFECI METEB

DESCRIPTION

As the st ate of the art in e lec tro nics p rogress es, m o r e tra nsi stors , F ETs,
and integrate d cir cu i ts are being used in rad io , telev i s i o n , and indu s tri a l
m a rket s. S e ncore engin e ers have kept up with todays pace and have de

veloped a new Field Effe ct m eter to mee t the more demanding requ i r e ment s
of sol id s ta t e and integrat ed cir cu it servi c i n g.

The F E20 HI-LO m e t er fea t ures new low AC and DC ranges of . 1 volts full
scal e and al o w power ohms circu it allowing for the f irst time a ccur ate re
sistance m e a s u r e ments in t ransisto r and integ ra ted circ uits.

Just co mpare these fe atur e s and see why the FE 20 is the most advanced
meter on the m a r ket today:

* High input impedance on all AC and DC ran g e s (15 megohm DC, 12 me g 

ohms AC).
* T r u e pe ak to peak AC r anges.
* Z ero ce nter ran g e s on DC for s olid s t a te servi cing.
* Db s cale fo r audio and lab work.
* DC cu rrent ranges for genera l tes tin g .
* Low power (low applied voltage) ohms ra n g e s for solid s t a t e s ervic ing.
* Mirrored sca l e m eter for g reater accu r acy in readings.
* Me t e r pro te ct e d fr om over loads.
* C i r cuits pr o te c te d from acc i d e n t a l ap pl icati on of wrong voltag es .
* All ste el carry i ng c ase with cover fo r grea ter durab il it y and portability.

* Long life "C" cell power.

DC VO LTS

SPECIFICATIONS

Ran g e s : 0 to .1 , .3, 1, 3, 10, 30, 100, 300, and 1000 full s cale

- .05 to. 05, - .15 to. 15, -.5 to. 5, -1.5 to 1 .5 , -5 to 5,

-15 to 15, -50 to 50, - 150 to 150, and -5 00 to 500 Z ero
Cent e r Scale Ran ges .

Input Re s istance: 15 megohms shunted by 90 pf in probe "NORM"

positio n ; or shunted by 10 pf in probe " 120K ISOLATION’
position.

Acc uracy : +1. 5%
AC Rejec t i on: 30 db Minimum

AC VOLTS
Ran g e s : (RMS)

0 to .1, . 3, 1, 3, 10, 30, 100, 300, and 1000 Full s cale

Ranges: (Peak to Peak)

0 to . 28, . 84, 2. 8, 8. 4, 28, 84, 280, 840, and 2800 F u l l scale

Input Resistance: 12 Megohms shunted by 9 0 pf

Freq u e n cy Res ponse : 1 db 10 Hz - 150 KHz

3 db 5 Hz - 500 KHz
OHMMETER
Ran g e s : HI & LO POWER

0 to 10 00 ohm s, 10K, 100K, 1 Meg, 10 Meg, 100 Meg, and

1000 Meg with 12 ohms ce nter scale
Accurac y: + 2 degree s ARC
Applied Voltage: Hi Power 1.5 Volts

Lo Power . 08 Vo lts

DC CURRE N T MEASUR E M E N TS :
Ran g e s : 0 to 100 mi c r oamps, 300 microamp s, 1 mA, 3 mA, 10 mA,

30 mA, 100 mA, 300 mA, and 1 amp.

Ac c u r acy: + 3% full s cale
Interna l voltage drop: 80 mv on 100 mic r o a m p to 10 mA r ange s ,

100 to 900 mv on 30 mA to 1 amp ra n ges.

Dec ib e l (db)
Ran g e s : -20, -10 , 0, 10, 20, 30, 40, 50, and 60 db

Refer enc e: 1 mv into 600 ohms

GENERAL SPECIFICAT IO NS:

M eter : 6 inch, 200 mic r o a m p , 2%
Mul tip lier resistors: 1/2% deposited ca r b o n type

Semiconductor com ple m en t :

T ransis to rs: 2 - 2N5457 FE Ts, 2 - 2N4248, 1 - 2N5172
Diodes: 2 - 1N456, 3 - 1N695, 1 - 16S10

Power supply: 6 e a c h 1. 5v " C" ce lls Evere a d y #935 or equivalent

(not supplied)

Ohms Batte r y : one 1. 5V "C" ce l l Eve re a dy #1035 or equivalent

(not supplied)
Weight: ( less b atteries) 8 lbs.
Dime n sions: 9 1/2” High X 7 3/4" Wide X 3 3/4" Deep.

The FE20 HI-LO Meter is equipped with a shielded tes t lead to allow ac
cu r ate meas u r e ments on AC in the presen ce of strong e lectr ost ati c and
ele ctromag netic fields. The special pro be has a 120K isola t io n res isto r
to iso l a t e the cab le capacity when making DC voltage m e a s urem e n t s in crit
ic al cir cuits such a s RF, IF or sweep cir cui ts. For a ll normal read in gs

including DC voltage, the pr o be switch is le f t in the n ormal position. The
only time that the switch is placed in the isola t e p o sitio n is when it i s nec
ess ar y to is olate cable cap a ci t y from the ci rcu it being m e a sured. When the

switch is in the isola t e po si tio n, the DC voltage rea di ng on the FE20wil l be
onlyO. 6% low. The isola t e position should only be used with the DC voltage
and AC voltage at 60 Hz functions as much greater e rro r will re sult on other

functions.
CONTROLS ON THE FE 20
The FE20 HI-LO Met e r i s a s simple to operate as a standard VOM. The

front panel c ontrols include the RANGE switch, FUNCTION switch, met e r

ZERO ADJUST, OHMS ADJUST, ON-OFF switch, and the batter y test

swit c h e s . The following i s a brief desc r i p t i o n of each c o n t r o l and how it is

Used:

RANGE Switch: The RANGE Switch sele cts the d esire d range of voltage,
cu rrent or resistan ce to be measu r e d .

FUNCTION Switch: The FUNCTION Switch sele cts the type of measu r e ment

to be made, plus or minus DC volts or curre nt, AC vo lts , HI or LO power
ohms.

ZERO ADJUST: The ZER O ADJUST is used to po sitio n the pointer of the
m eter ov e r the ze r o at the extreme left of the me t er for m o s t mea s u r e ment s ,
or ove r the cen t er z ero for the z ero ce nter ranges.

OHMS ADJUST: The OHMS ADJUST i s adjusted with the FE 20 le a ds held
open. The OHMS ADJUST co ntrol is adjusted so that the po in ter of the me t e r
is positioned di rect l y o ver the infinity ma r k on the extreme right hand side
of the meter. Th e ohms zero is adjusted with the test leads shorted togeth er
and the Range Switch s et to any posi t io n ex c ep t RX1 or RX10 .

ON - OFF Switch: The O N-OF F Switch controls the power to the m e t er cir
cuit . In the OF F position, the b atteries ar e disco n nect ed f r o m the me t e r
circ uits. In the ON position, b a t t e r y power is applied to the m eter circui try
and the mete r is re a d y to go. When the lid of the FE20 is shut, a s pecia l
tab autom a t ic a ll y shuts o fft heFE20 to be su r e that the ba tteries do not wear

down nee d le s sly.
BAT T E RY T EST Swit ch es : The FE20 use s two bat t e r y test sw it c he s . The

bat t e r y t est switch on the l e f t is the t est fo r the main (power) b a t te r y , and
the switch to the rig h t is the ohms ba t t ery t e s t.

The S e n c o r e FE20 is s im p le and easy to opera t e . The long li f e "C " cell

power supply allow s the FE20 to ope ra te anytime, anywhere.

Batt e r y Inst al la tio n and Test ing: To gain ac cess to the bat tery compartmen t,
remove the two s crews in the lead compa rt m en t . Lift out the lead c om

partm e n t, exposing the batte r y ho l d ers.

Th ere a re two power supp lies used in your F E20. Six "C" ce lls are con 
nected in series to power the amplif ier and bridge circuit, and one "C" cell
is used to power the ohms function. To install the s ix "C " c ells for the
bridge power supply, plac e 3 "C" cells in each of the two tubes provided.
Inst a ll the tubes containing the th re e batte ries each , between the spring
bat tery conta cts. Be s ure to o bserve pola r i t y . The ohms ba t t e r y is in s ta l le d
in the single bat t e r y hold er that is mounted at an angle. It i s recomm ended
that a "p r e mium " cell be used in this app lication as the c urre nt drain can
be quite high when using the RX1 HI power ohms range.

The two s prin g r e t urn slid e switche s on the front panel of the FE20 provide
a batte ry c heck function. Push the Ohms switch to the righ t to test the con
dition of the o h m s bat t e ry, and push the Main switch to the l eft to t est the
condition of the bridge power supply b a t t e r y .

Operatio n : To o p e ra t e the F E20, mer ely select the desire d test with the

Function switch, the app ro p ri ate rang e with the Range switch, connect the
test lead s to the points being measu r e d , and obs e r v e the indication on the

m eter. H er e is a bri ef desc r i p t ion of how each test is p e rf o r m e d .

Meas u r in g DC V o lt s : Set the switch on the pro be to the NORM po s it io n ; set

the Function switch to eit her the plus or minus DCV positio n; se t the Range
switch for a mete r indication a s c l ose to full sc ale as possible. (I f the volt

age to be me a s u r e d is unknown, start with the 1000 volt range and work

toward the 0.1 volt range).
The DC voltage is rea d on the two blac k scal es j ust above the mir ro r on the

m eter. The top DC sc ale i s calibr ated from Oto 1.0 volts, with each smal l

sc ale division r epre s enting . 02 volts, and is used with the . 1, 1, 10, 100,

and 1,000 volt ran ges. The second DC scal e i s c a l i brated fr o m 0 to 3.1

volts with each s mall s cal e division repr esen t i ng 0.1 volts, and is used for
the . 3, 3, 30, and 300 voltr ang e s . l i ieO to 1.0 v olt scale i s readdi rec tly

for the 1.0 volt range, and is multiplied by . 1, 10, 100, and 1,00 0 for the

.1, 10, 100, and 1,000 volt ran g es respectively. The 0 to 3 .0 volt scal e
is rea d di r ectl y for the 3. 0 volt range and is multiplied by . 1, 10, and 100

for the . 3, 30, and 300 volt ranges re spectiv ely. For Exam p le: If the sca l e

indication i s . 42 on the 0-1 vo l tsc ale and the Range switch is set to the 10
volt range, you would multiply . 42 by 10 r esult i n g in an actu al reading o r

4.5 volts. If the scal e indication is 1. 6 on the 0 to 3 volt scal e and the

Range switch is se t to the 0. 3 ra n g e , the actu a l reading would be . 16 volts.