Power Distribution Circuits and Components-continued

TM 11-5820-I509-

Item

Indication

Probable trouble

Procedure

-110-volt dc bias circuit in PA

Rotate XMTR PWR switch to

filter box FL2 defective.

OFF and check continuity from

FL2-7 to FL2-20 (normal 29

ohms); check for shorts to

ground. Replace C222, C209,

C233, or L201 as required or

repair circuit.

-110-volt bias circuit between

Check continuity from J1-9 to

J1-9 and FL2-7 defective.

FL2-7; repair as required.

-110-volt bias circuit between

Check continuity from S103-1 to

S103 and J102 defective.

L102; repair circuit if necessary.

Check C101B for shorts; replace

if necessary.

J102 circuit defective.

Check continuity from J102 to

S103-1 (normal 10K ohms).

Replace R103 or J102 as

required.

WARNING.

The 650- and 1600-voit potentials at the power amplifier screen and plate electrodes are extremely dangerous. Avoid contact

with these circuits.

Plate and screen voltages to power

a. +650-volt screen circuit

a. Check continuity of screen

amplifier stage is low or not

defective.

circuit from J1-A1 to C30, from

present.

C30 to L123-1, from L123-2 to

S103A-5, to S103B-3. Repair

circuit if open.

b. Capacitor C30 shorted to

b. Check C30 for short to ground;

ground.

replace if necessary.

c. Switch S103 defective.

c. With XMTR PWR switch at

LO, check continuity from

S103A-3 to S103A-5; from

S103B-10 to S103B-11. Rotate

XMTR PWR switch to HI and

check continuity from S103A-3

to S103A-8 and from S103B-3 to

S103B-10. Replace S103 if

defective.

d. Screen grid voltage divider

d. With XMTR PWR switch at

defective.

HI, or OFF, check resistance

between S103B-11 and S103B-3

(normal 50K ohms) and between

S103B-11 and chassis ground

(normal 100K ohms). Replace

R105, R106, and/or R128 if

defective.

e. Screen grid circuit from S103B-

e. Check continuity from S103B-

10 to power amplifier socket

10 to K102-7, from K102-8 to

defective.

K102-4, and from K102-3 to

L103-1. Resistance of L103 is 50

ohms. Check continuity from

L103-2 to XV101-2 and XV101-

6. Check C139 for short to

ground. Repair circuit or replace

L103 or C139 if defective.

Screen voltage relay K102 filter

Check continuity across C146

network defective.

and measure resistance of R125

(normal 560 ohms). Replace

C146 if shorted and R125 if

defective

g. Plate circuit from S103A-3 to

g. Check continuity from S103A-3

power amplifier plate electrode

to R112, to L106-1, from L106-2

defective.

to 1.109-1, and from L109-2 to

V101 plate cap. Measure

resistance of L106 (normal 2.1

ohms) and L109 (normal less

than 1 ohm) and check C123 for

short to ground. Repair circuit,

or replace C123. L106.

L104 /R110, or TUNE coil L109.

3-80