Figure 5-3. Power Supply PP-3940A/G, Component Board A3, Parts Location Diagram.

TM 11-6130-247-14-1

Figure 5-3. Power Supply PP-3940A/G, Component Board A3, Parts Location Diagram.

h. Connect variable power transformers to the 115-

ters R53A and R53B and VOLT ADJ coarse and fine

volt, 1-phase, 60-Hz source. Adjust variable power

control potentiometers R59A and R59B maximum

transformer to 115-volt output as viewed on Multim-

clockwise.

eter TS-352B/U.

j. Connect voltmeter (AN/GSM-64) between termin-

al E2 and the junction of resistors R37 and R36.

5-6. Preregulator and Reference Supply

k. Set A3R57 so that voltmeter indicates approxi-

Adjustment

mately 5 volts.

a. Set POWER switch S1 to ON and observe that

l. With the output voltage set to 40 volts dc and the

POWER ON indicator and VOLT MODE lamp light.

input line set to 105 volts ac, gradually increase the

b. Connect frequency counter (N/USM-207A)

load to full current output (4 amperes).

across resistor A4R7 and adjust potentiometer A4R4

m. At this load setting, reset potentiometer A3R57

to frequency of 4,000 Hertz ± 400.

to 5.0 Volta ± 0.1.

c. Gyptol potentiometer A4R4.

n. Lock with Gyptol.

d. Remove frequency counter.

NOTE

e. Connect oscilloscope (AN/USM-281) across re-

If output current level cannot be reached,

sistor A4R25. Check for clean square wave driving

gradually and with caution adjust potentiom-

pulse across entire duty cycle range. If pulse is not a

eter R54 until proper output current is ob-

clean square wave, troubleshoot components on circuit

tained.

board A4.

3-7. Current Mode Range Adjustment

f. Remove oscilloscope.

g. Place voltmeter (AN/GSM-64) across capacitor

a. Set POWER switch S1 to off and insert an am-

A3C23 and adjust potentiometer R69 so that

meter (Multimeter ME-452) in series with the load.

voltmeter indicates 12.0 to 12,2 volts.

b. Set CUR ADJ coarse and fine controls fully

NOTE

counterclockwise.

Do not use Gyptol on potentiometer R69 at

c. Set POWER switch S1 to ON and adjust potenti-

this time. Further adjustments are required.

ometer A3R50 as follows.

h. Vary input line from 105 to 125 volts ac using

(1) Set potentiometer A3R50 until load current is

variable transformer. The regulation should be 0.5

set as close as possible to zero but some current is still

millivolt or less.

indicated.

i. Set CUR ADJ coarse and fine control potentiome-

(2) Continue to turn potentiometer A3R50 1 or 2

5-3

Change 1