Replacement of Decimal Point Indicator Lamps

TM 11-6625 -537-14-1

will normally disappear after the tube has aged a

V202 and chopper CK1 on the dc vtvm printed

circuit board with Humi-Seal IBI2 (manufactured

bit. When replacing V102, use a type 0G3 which

by Columbia Technical Corp., Woodside, N, Y.) to

has been aged for at least 150 hours to obtain

prevent moisture accumulation, When replacing

stable operation. The electronic voltmeter should

be recalibrated after replacing any components.

tube V104 or V105 (12AX7), some drift of the 500-

volt dc reference supply may be noted. This drift

Table 6-2. Test Procedure for Fault Isolation

Resistor

Nominal resistor voltage

Maximum voltage difference

each resistor

R401 and R402

.01

R403 and R406

100.5

.02

R407 and R408

.001

R409 and R417

.002

R418 and R419

.0001

.05

R420 thru R428

.0002

R429 and R430

.05

.00001

R431 thru R439

.00002

.01

R440 thru R449

.0000O1

.001

6-12, Replacement of Decimal Point Indicator

g. Remove decimal lamp holder from bracket

Lamps

by applying pressure to each side of holder,

h. Remove cardboard shield and replace bulb.

a. Disconnect power cord from power source.

i. Place card board shield over bulb and replace

b. Remove screws at back of cabinet and slide

holder in bracket.

instrument out of case.

j. Install range resistor printed circuit board

c. Remove screws that hold front panel

and precision voltage divider printed circuit board

assembly to chassis.

on front panel assembly.

d. Being careful to avoid wiring damage,

k. Install front panel assembly on chassis,

gently lift front panel assembly from instrument

L Replace instrument in case and install screws

and place face down in front of instrument.

at back of cabinet.

e . Remove screws holding range resistor

m. Allow electronic voltmeter to remain in

printed circuit board and precision voltage divider

normal upright position for at least 8 hours before

printed circuit board to front panel assembly,

operation. This will allow voltage of standard cell

f. Push these printed circuit boards aside

to return to normal after being tipped.

enough to allow access to decimal lamp holders.