Power Supply Card A12 Test Theory.

TM 9-4931-363-14&P

(4) Refer to step 3 in figure 2-11 and in the A12 test

2-17. Power Supply Card A12 Test Theory.

table. To provide a check of the power fail circuitry on the

a. Reference Material. The following reference

A12 card, three power inputs, in addition to those provided

in step 1, are required. The 10 volts ac, in phase, is

materials are required to support the power supply card

A12 test theory discussion:

connected through wiper 1 and contact 8 of S4-D, and

through wiper 1 and contact 9 of S8-C to J6-12. The 10

(1) Power supply card A12 test table from TM

volts ac, out of phase, is connected through wiper 1 and

9-1270-212-14&P

contact 8 of S4-E, and through wiper 1 and contact 9 of

S8-D to J6-14. The 28 volts dc is connected through wiper

(2) Power supply card A12 foldout schematic from

1 and contact 8 of S4-A, through CR6, and through wiper 1

TM 9-1270-212-14&P

and contact 9 of S8-A to J6-22. The logic high at J6-6 is

applied to X42-31 in the test set. When S11 is pressed, 28

(3) Power supply card A12 test functional diagram

volts dc is connected through wiper 1 and contact 8 of

(fig. 2-11).

S4-B, and through wiper 1 and contact 9 of S8-E to

XA2-33. The activated logic circuitry provides a ground at

b. Theory Discussion.

XA2-27 which lights DS7 on the test set.

(1) To prepare for the power supply card A12 test

(5) Refer to step 4 in figure 2-11 and in the A12 test

theory discussion, refer to the troubleshooting procedures

table. With S8 set to position 9, the +12-volt output of the

for power supply card A12 in TM 9-1270-212-14&P and

card at J6-34 is connected through contact 10 and wiper 1

mentally perform steps a through e.

of S8-L, and through contact 6 and wiper 1 of S5-A to the

meter input.

(2) Refer to step 1 in figure 2-11 and in the A12 test

table. The A12 power supply card under test is connected

(6) Refer to step 5 in figure 2-11 and in the A12 test

to J6 on the test set. With S4 set to position 7, the primary

table. With the A12 card bridge rectifiers activated as in

winding of T1 in the test set is energized. The 28 volts dc is

step 1 but the three added power inputs of step 3 removed,

connected through wiper 1 and contact 8 of S4-A to

the output of the power fail circuit at J6-6 is a logic low.

energize K9 and K10 in the test set. The energized contacts

Thus, when S11 on the test set is pressed to activate the

of relays K9 and K10 disconnect the two 20-volt

test set power fail logic, XA2-27 remains a logic high and

transformer windings of T1 from the A12 card in the test

DS7 is not lighted.

set and connect the windings to the A12 card under test.

The 10-volt windings remain connected to both A12 cards.

(7) Refer to step 6 in figure 2-11 and in the A12 test

With S8 set to position 7, the -18-volt dc output of the card

table. With S8 set to position 10, the +5-volt dc output of

at J6-10 is connected through contact 8 and wiper 1 of

the card at J6-32 is connected through contact 11 and

S8-L, and through contact 6 and wiper 1 of S5-A to the

wiper 1 of S8-L, and through contact 6 and wiper 1 of S5-A

meter input.

to the meter input.

(3) Refer to step 2 in figure 2-11 and in the A12 test

(8) Refer to step 7 in figure 2-11 and in the A12 test

table. With S8 set to position 8, the +18-volt dc output of

table. With S8 set to position 11, the -6-volt dc output of

the card at J6-30 is connected through contact 9 and wiper

the card at J6-18 is connected through contact 12 and

1 of S8-L, and through contact 6 and wiper 1 of S5-A to

wiper 1 of S8-L, and through contact 6 and wiper 1 of S5-A

the meter input.

to the meter input.

2-56