Section III. MAINTENANCE OF THE VOLTMETER

TM 11-6625-444-14-1

and select VDC and FILT mode. Insure 10V

(3) Apply +10V DC to A10TP4 (-) and TP5

range is selected.

(+). The voltage at A10TP5 and TP3 shall not

(6) Apply a 3V rms ±1 %, 60 Hz signal to the

change more than ± 100 µV.

INPUT terminals.

(4) Apply -10V DC to A10TP4 (-) and TP5

(7) Rotate SAMPLE RATE control to obtain

(+), observing that the voltage at A10AP5 and

a digital readout change of approximately two

TP3 does not change more than ±100 µV. If the

times a second. The digital readout shall be less

preceding are ae specified, the active filter is

than +20 digits. If not, the filter circuitry is

operational. If not, the gain control circuitry is

defective.

fault y.

(5) Disconnect equipment from the voltmeter

Section III. MAINTENANCE OF THE VOLTMETER

switches. Retain gaskets freed upon removal of

6-9. General

front panel.

This section contains maintenance instructions

(6) Unplug and remove printed circuit boards

for the voltmeter. The information is arranged

(E), except for the printer output (A7) which is

under paragraphs covering disassembly,

attached to the rear panel by its cabling.

cleaning, repair and replacement, assembly, and

(7) Cut cable ties (F) at rear panel INPUT

component selection. Contents of these

harness, inner chassis transformer secondary

paragraphs provide complete maintenance in-

harness, and inner chassis power harness (two

structions for the voltmeter. The performance

places).

tests in paragraph 6-16 shall be conducted after

(8) Disconnect transformer harness at TB2

any repairs are made.

(G) and pull harness out and away from chassis.

6-10. Disassembly

(9) Tag and disconnect rear INPUT terminal

a. Covers. Removal of dust covers and inner

wiring (H). Wiring is disconnected by removing

guard covers is accomplished as follows:

nuts on each terminal.

(1) Remove top dust cover by unlocking

(10) Tag, unsolder, and disconnect rear panel

fasteners.

GUARD wire (I) at inner chassis.

(2) Remove top guard cover by removing four

(11) Remove 12 screws (J) which attach inner

attaching screws.

chassis to main chassis.

(3) Remove bottom dust cover by unlocking

(12) Pull EXT REF input cabling (K) toward

fasteners.

the front of the voltmeter until free of the inner

(4) Remove bottom guard covers by

chassis.

removing single attaching screw from rear-most

(13) Slide the inner chassis (L) forward while

cover and four screws from front bottom cover.

at the same time lifting its rear section up. Make

b. Panels and Chassis. Disassembly of the

sure the cable clamp and cabling on the right, rear

panels and chassis is done in the sequence shown

section stays on the side near the rear of the

in figures 6-23 and 6-24 together with the

voltmeter.

Referenced letters

following procedure.

(14) Remove the inner chassis by first pulling

correspond with those shown in figures 6-23 and

the inner chassis up and towards the rear of the

6-24.

voltmeter. Next, apply a slight upward pressure

(1) Remove each control knob (A, fig, 6-23)

on the front section (M) just before the RANGE

on the front panel by loosening setscrews.

and SAMPLE RATE controls bottom out against

(2) Remove seal nuts (A) associated with

the chassis and then remove the inner chassis.

each control shaft.

Position inner chassis as shown in figure 6-23.

(3) Tag, unsolder, and disconnect wire from

(15) Straighten locking tabs on the DC

GUARD terminal (B) at terminal riveted to

ZERO and RATIO FULL SCALE poten-

chassis.

tiometers (N, fig. 6-24) and then push them free of

(4) Tag and unplug wiring (C) to INPUT

panel.

terminals.

(16) Remove inner front panel by removing

(5) Remove the front panel (D) by first

seven screws (0).

removing 12 attaching screws. Next, carefully

(17) Remove four screws (P) which secure the

pull front panel free of pushbutton switches while

rear of the display assembly (A14).

at the same time removing the boots from the

6-23