Synchro Electrical Zeroing (CRC).

TM 55-4920-430-13

(3) Set the METER switch to AC. Set the METER RANGE switch to 200MV.

(4) Turn the zero-width adjust screw on the meter fully clockwise.

(5) Adjust the input offset null screw on the meter for minimum reading on the AC/DC

VOLTMETER.

(6) Turn the zero-width adjust screw counterclockwise until the AC/DC VOLTMETER reads

+00.0.

e. Adjust gain as follows (fig. 4-4).

(1) Set the METER switch to DC.

(2) Set the METER RANGE switch to 20V.

(3) Set the SELF TEST CIRCUIT SELECT switches to 00,3.

(4) Set the digital multimeter to 20 volt dc range. Connect the test leads of the multimeter to EXT

METER JACKS HI and LO. The digital multimeter shall read 14.900 to 15.100.

(5) Turn the AC/DC VOLTMETER gain adjust screw until the AC/DC VOLTMETER reads the

same as the digital multimeter, to 3 decimal places.

(6) Set the SELF TEST CIRCUIT SELECT switches to 00,4. The digital multimeter shall read

-14.900 to -15.100.

(7) Turn the zero-width screw until the AC/DC VOLTMETER reads the same as the digital

multimeter, to 3 decimal places. Set SELF TEST CIRCUIT SELECT switches to 00,3. Note the reading.

(8) Adjust the gain adjust screw until the AC/DC VOLTMETER reads the same as the digital

multimeter.

(9) Repeat steps (6) through (8) as required until AC/DC VOLTMETER and digital multimeter

readings are equal.

(10) Disconnect the digital multimeter and install the AC/DC VOLTMETER lens.

4-38. Synchro Electrical Zeroing (CRC).

Zero ATT synchro B1 as follows. (See fig. 4-5.)

a. Connect plug P1 of power cable W7 to test set POWER receptacle J7. Connect plug P2 to a 115-

volt ac power source. Connect plug P3 to a 28 volt dc power source.

b. Set the 115V 400 Hz, and +28 VDC TESTER POWER switches to ON. Allow 2 minutes, for

warmup. Check that MODE switch is at OFF. If the HOLD/STIM light is on, set the MODE switch to

ON, then OFF.

c. Set the ATT SELECT switch to ROLL. Turn the ATT synchro dial to 180.

d Set the digital multimeter to the 20-volt range. Connect the multimeter test leads to receptacles J3-

pins, U (line) and V.

e. Connect oscilloscope CHANNEL A across the digital multimeter. Keep it connected to those leads

throughout the test.

f. At the rear of the synchro, loosen three screws on the stator.

g. Adjust the synchro stator for minimum reading on the digital multimeter.

h. Tighten the three screws on the synchro stator.

i. Connect the multimeter to receptacle pin J3-T (line) and pin J1-D. Connect jumper wire between

pins J1-D and J3-V.

j. Connect oscilloscope CHANNEL B to receptacle pin J1-B.

k. Check that the multimeter indicates 9.2 to 11.2 volts ac. Check that CHANNEL A and B wave-

forms are in phase. If not, proceed to step n.