Checking Power Supply Section and B+output Circuits for Shorts

TM 11-6625-667-45/NAVSHIPS 0969-249-8010/NAVAIR 16-30APM123-2/TO 33A1-3-367-22

Section Il. TROUBLESHOOTING TEST SET, TRANSPONDER AN/APM-123(V)1

Caution: Do not attempt removal or replacement of parts before reading the instructions in

paragraph 4-1.

(1) Set PANEL LIGHT switch to OFF.

3-5. Checking Power Supply Section and B+

(2) Remove modules A13 and A14 (fig. 3-6).

output Circuits for Shorts

(3) Remove extender board and insert in

a. When to Check. When any of the following

module A13 receptacle.

conditions exist, check for short circuits and,

(4) Disconnect plug A16P2 (fig. 3-7) at the

unless otherwise specified, remedy trouble before

transmitter by removing the two screws securing

applying power:

the plug to chassis, then carefully pull it out.

(1) When fuses continually blow.

c. Measurements.

(2) When abnormal symptoms during sec-

Caution: This equipment is transistorized,

tionalization tests indicate possible B + trouble.

refer to paragraph 3-7 for instructions Do not

b. Conditions for Tests. Prepare the equipment

use the RX1 scale or multimeter.

for short circuit tests as follows:

Point of measurement

Normal indication

Isolating procedure

Step

1 Pins 10 and 22 of

40 ohms + 20% (mul-

If normal, proceed with step 2. Zero resistance indicates trouble

extender board.

timeter scale RX

in the 28-volt supply.

100).

a. Infinity (∞) ohms

2 Pins land l0 of

a. Reconnect plug A 16P2 to jack A 16J2. If the resistance is

extender board.

(multimeter scale

zero, remove transmitter (para 3-10) and check socket

RX10K),

resistances of subassembly A16A2 (fig. 3-10) with plug

A16P2 disconnected. If the resistance is normal, proceed

with b below.

b. Insert module A 16 into its receptacle and observe meter

b. 40 ohms + 20%

(multimeter scale

indication. Zero resistance indicates trouble in module A14.

RX100).

If resistance is normal, proceed with c below.

c. ∞ ohms (multimeter c. Remove module A 14 and extender board. Insert the card

scale RX1OK).

extender board into the module A 14 receptacle, and module

A13 into its receptacle. An abnormally low resistance (200K

or less) indicates trouble in module A 13. If the resistance

is normal, proceed with step 3.

3 Test points A13TP1

1,100 ohms 20%

Remove modules A4, A5, and A7 through A12. Check the

(positive lead) and

(multimeter scale

resistance between these points A13TP1 and A13TP2. If

A13TP2 (ground).

RX1OO).

normal, proceed with step 4. If the resistance is abnormally

low, proceed as follows:

a. Insert module A14 and observe resistance. If resistance

decreases, the trouble is in the l8-volt power supply of

module A14. If resistance does not decrease, check wiring

(fig. 8-16); if the wiring is not shorted, proceed with b below.

b. Insert modules A4, A5, and A7 through A12 one at a time and

observe resistance. If the resistance decreases to less than

500 ohms with the insertion of a module, the trouble exists

in the B input of that module.

4 A13TP3 (positive

120 ohms 20%

Remove modules A4, A5, and A7 through A12 and repeat step

lead) and A13TP2.

(multimeter scale

2b. If resistance is zero with the insertion of a board, the

RX1).

trouble exists in the B+ circuits of the board.

3-15