Section IV. REMOVAL AND REPLACEMENT

TM 11-5821-277-20

Trouble symptom

Probable trouble

Checks and correctlve measures

Item No.

Transceiver squelch control not ad-

Replace transcei

Excessive noise in headset

ver

(para

4-17).

during periods of no signal

justed properly.

reception.

Audio signals are distorted,

a. Transceiver defective ------------------

Replace transceiver (para 4-17).

or contain excessive hum.

b. Connect headset and microphone di-

b. Aircraft Cl61lD/AIC defective __

rectly to transceiver PHONE and

MIKE jacks and operate radio act.

If distortion or excessive hum is no

longer present, trouble is isolated to

C-1611D/AIC. Refer C-1611D/AIC

to higher category maintenance for

repair.

c. Audio cables defective, or shield

Request higher category maintenance

check of audio cabling.

not properly grounded.

Radio set operates on some

a. Replace control unit (para 4-16).

a. Control unit defective . . . . . . . . . .

frequencies but not on

others.

b. Replace transceiver (para 4-17).

b. Transceiver defective ------------------------

a. Replace transceiver (para 417).

Reception and transmission

a. Transceiver defective ---------- - - - - - - - - -

very weak

b. Request higher category maintenance

b. Antenna or antenna rf intercon-

check of antenna and associated rf

necting cabling defective.

cabling.

Replace control unit (para 4-16).

VOL control defective . ---------------

Operation of Control Unit

VOL control does not

change received audio sig-

nal.

Worn or damaged resilient mount(s)

Replace resilient mounts as necessary

Mounting does not operate

(para 4 - 1 8 ) .

smoothIy or provide speci-

fied limits of travel to

protect transceiver from

shock and vibration.

Section IV. REMOVAL AND REPLACEMENT

4-14. Control Unit Panel Lamp

4-15. Control Unit Control Knobs

a. The MHz timing control knob and the OFF-

WARNING

PWR switch are on the same mounting shaft, and

Be sure that the 27.5-volt dc circuit

the VOL. control knob and the kHz tuning c o n -

breaker that supplies power to the radio

trol knob are on the same mounting shaft ( f i g .

set is deenergized before performing the

3 - 1 ) ; however, each of the knobs is a separate,

procedures given below.

i n d e p e n d e n t section. When replacing the r e a r

sections, it is necessary to first remove the associ-

NOTE

ated tuning control knob.

Check to see that the washer and rubber ring re-

b. Perfor-m the procedures given below when

m a i n in place on the lampholder during removal

removing and replacing the control knobs.

procedures.

CAUTION

a. Unscrew

the

defective

lampholder

from

the

When replacing a rear section knob,

panel.

check to see that it does not drag or

b . Remove the defective l a m p from holder

bind against the front panel of the con-

w i t h a sharp-bladed instrument to separate the

trol unit after the setscrews that hold it

base of the lamp from the holder,

in place have been tightened. Also check

c. Insert a new lamp firmly into the holder.

to see that the front knob does not bind

or drag against the rear knob after the

d. Screw the lampholder

into the front

firmly

setscrews have been tightened.

panel of the control unit.

4-9