Front Loop and Back Loop Adjustment (R732 and R742)

TM 11-6125-259-30

CAUTION

b. Unsolder wire at pin (13) of component assembly

When performing d and e below, make

A5Al (see fig.3-16).

sure components, pin and printed wiring

c. Connect a 30 vdc, 0-5 amps power supply to

on A7 component assembly (17) do not

pins 13(+) and 14(-) of component assembly A5A1.

touch chassis ground; do not damage

d. connect Digital voltmeter AN/GSM-64 to

interconnecting wiring.

pins 12(+) and 14-) of component assembly A5A1.

e. Adjust power supply voltage to 25.0 1.0 vdc.

d. Carefully lay back upper end of A7 assembly

Adjust potentiometer R511 until the digital volt-

(17) 90 degrees over on to work bench; do not put

meter indicates 14.00 0.01 vdc.

strain on interconnecting wiring.

f. Disconnect 30 vdc power supply and digital

e. Loosen A6 component assembly (16) by

voltmeter. Resolder wire to pin 13 of component

removing six spacers (23); and two nuts (24), two

assembly A5A1.

lockwashers (21) and two flat washers (22).

g. Install top cover (1, fig. 3-21) with 34 screws

f. Carefully move lower end of A6 component

assembly (16) a few inches forward as necessary to

(3) and 34 flat washers (2).

gain access to adjustment screws of R627 (and R635

3-13. Front Loop and Back Loop Adjustment

for para 3-15) potentiometers (see fig. 3-17); do not

(R732 and R742)

put strain on upper interconnecting wiring.

a. Remove bottom cover (18, fig. 3-21) by

g. Connect Digital Voltmeter AN/GSM-64 to

removing six screws (19).

pins TP1(+) (fig. 3-17) and 7 (-) of component

b. Connect inverter to test fixture in accordance

assembly A6.

with fig. 3-19.

h. Connect Oscilloscope AN/USM-281 and

c. On component assembly A7 (fig. 3-18) adjust

Electronic Counter AN/USM-207 to pins 15 (+) and

potentiometer R732 (front loop adjustment) and

12().

potentiometer R742 (back loop adjustment) full

i. Connect inverter to test fixture in accordance

Counterclockwise.

with fig. 3-19.

d. On test fixture, set UNIT PWR switch S6 to

j. Set UNIT PWR switch S6 to ON position and

ON position and gradually apply +28.0 2.0 vdc.

apply 25 1 vdc to input as read on digital volt-

e. Adjust potentiometer R732 clockwise until

meter No. 1.

Digital Voltmeter AN/GSM-64 No. 4 indicates

k. Adjust potentiometer R627 for an indication of

115.0 0.1 vdc.

4.000 0.005 on the digital voltmeter.

f. Set switches S2, 3, 4, 12, 13, 14, 22, 23, 24 to the

l. The oscilloscope shall display a waveform as

up (on) position to apply 250 VA load on all three

shown in figure 3-2 and the electronic counter shall

output phases. Adjust potentiometer R742 until

indicate 400 1 Hz.

digital voltmeter No. 4 indicates 115.0 9.1 vdc.

m. If the electronic counter does not read 400 1

g. Set switches S2, 3, 4, 12, 13, 14, 22, 23, 24 to

Hz, change resistor R608 value to obtain a

the down (off) position (no load). Adjust poten-

frequency indication of 400 1 Hz.

tiometer R732 until digital voltmeter No. 4 reads

n. Set UNIT PWR switch S6 to down (off)

115.0 0.1 vdc.

position and disconnect digital voltmeter,

h. Repeat d through g above until the output

oscilloscope and electronic counter.

voltage regulation from no load to 250 VA is within

o. Disconnect inverter from test fixture.

0.1 vac.

NOTE

i. Deenergize the input power supply and

Perform p, q, and r below only if

disconnect inverter from test fixture.

paragraph 3-15, input overvoltage ad-

j. Install six screws (19, fig. 3-21) and bottom

justment, will not be performed next. If it

cover (18).

will be performed, go directly to

paragraph 3-15.

3-14. Frequency and Protective Circuit

Reference Voltage Adjustment (R627)

p. Install A6 component assembly (16, fig. 3-21)

to housing (12) studs with six acers (23); and two

a. Remove bottom cover (18, fig. 3-21) by

nuts (24), two lockwashers (21) and two flat washers

removing Six screws (19).

(22).

b. Loosen A7 component assembly (17) by

q. Carefully lay A7 component assembly (17)

removing six screws (20), six lockwashers (21) and

back in place on top of A6 assembly (16); be careful

six flat washers (22).

of interconneting wiring. Install A7 component

c. Place unit with front side down on workbench.

3-23