AM-2060(*)/GRC, Isolating Troubles in Audio Amplifiers Q1 and Q2

TM 11-5820-496-35

(3) Transmit dummy load assembly (para

3-9. AM-2060(*)/GRC, Isolating Troubles in

3-3e, fig. 3-1).

Audio Amplifiers Q1 and Q2

b. Test Setup.

When trouble has been localized to audio ampli-

(1) Remove the access plate (fig. 3-10)

fiers Q1 and Q2, use the following procedures

from the top of the AM2060(*)/GRC to gain ac-

to isolate the defective part in the circuit.

a. The following equipment is required:

cess to the test points El through E22 on the

plug-in assembly (fig. 3-9).

(1) A 25.5-volt dc power source (or 25.2-volt

(2) Connect the transmit dummy load as-

output of Power Supply PP2953(*)/U).

sembly to SET POWER connector J2 (fig. 38).

(2) Generator, Signal AN/URM-127.

(3) Voltmeter, Electronic ME-30(*)/U.

(3) Connect the dc power source (a(1)

(4) Receive dummy load assembly (para

above) to pins A (chassis ground and J of

POWER INPUT connector J3 (fig. 3-8).

3-3e, fig. 3-1).

b. Remove the access plate (fig, 310) from the

(4) Set the PWR switch to ON.

top of the AM2060(*)/GRC to gain access to the

c. Output Voltage Adjustments, R1O.

test points El through E22 on the plug-in assem-

(1) Perform the test setup given in b above.

bly (fig. 3-11 and 3-15).

(2) Connect the ME-26(*)/U, arranged as a

c. Connect the receive dummy load assembly to

dc voltmeter, between pins E (positive) and A

SET POWER connector J2 (fig. 3-7).

(chassis ground) (14.5-ohm load resistor) of

d. Connect the dc power source (a(1) above) to

SET POWER connector J2 (fig. 38).

pins A (chassis ground) and J of POWER INPUT

(3) Loosen the locknut holding the adjust-

connector J3 (fig. 37).

ment screw of R10 (fig. 311).

e. Set the PWR and SPKR switches to ON.

NOTE

f. Apply a 1-kHz, 1-volt signal from the

If the locknut cannot be easily loosened, use

AN/URM-127 with its adapter UG514/U to pins

a drop of penetrating oil on the threads and

A (chassis ground) and B of SET POWER

allow it to penetrate before trying to loosen

connector J2 (fig. 3-7).

the locknut.

g. When the ME30(*)/U is connected between

(4) Adjust R10 adjustment screw for an in-

pins E1 and E14 of the plug-in-assembly (fig.3-9),

dication of +13 volts on the ME-26(*)/U. Fin-

it should indicate 4.5 0.10 volts ac. If the

gertighten the locknut holding the control.

ME-30(*)/U indication is not approximately 4.5

d. Isolating Troubles in Voltage Regulator Cir-

volts ac, make voltage and resistance measure

cuit Q3 and Q4.

ments of the audio amplifier circuit and also the

(1) Perform the test setup and adjustment

voltage regulator circuit.

procedures given in b and c above before proceed-

(1) To make the voltage measurements, leave

ing.

the dc power connected to connector J3 (d above)

(2) Measure the voltage drop across refer-

and make the voltage measurements at the pins of

ence diode CR1 by placing the ME-26(*)/U nega-

the plug-in assembly (fig. 39).

tive lead on test point E1 and the positive test

(2) TO make the resistance measurements,

lead on test point E6 (fig. 3-9). The ME-26(*)/U

remove the dc power from connector J3, and make

should indicate approximately 6.8 volts dc.

the resistance measurements at the pins of the

(3) Measure the voltage drop across ref-

plug-in assembly.

erence diode CR2 by placing the ME26(*)/U

(3) Refer to paragraph 3-11 for dc resist-

negative lead on test point E3 and the positive

ance of transformers and coils involved in the

test lead on test point E4. The ME26(*)/U

circuits.

should indicate approximately 6.8 volts dc.

(4) If the voltage indication obtained across

3-10. AM-2060(*)/GRC, Adjustment of R10,

CR1 and CR2 is still not within limits, make volt-

and Isolating Troubles in Voltage Regu-

age and resistance measurements of the voltage

lator Circuits Q3 and Q4

regulator circuits to determine the defective part.

When trouble has been localized to voltage regula-

tors Q3 and Q4, use the following procedures to

3-11. Dc Resistance of Transformers and Coils

isolate the defective part in the circuit.

The dc resistance of the transformer windings

a. Equipment Required.

and the relay coil on the plug-in assembly of

(1) A 25.5-volt dc power source (or 25.2-

the AM-2060(*)/GRC are listed in the following

volt output of Power Supply PP-2953(*)/U).

chart.

(2) Multimeter ME-26(*)/U.

3-9