TM 11-6625-2958-14&P

5-7, the circuit is checked by starting with the output waveform and tracing backwards.

5-61 Performing the tests given in Table 5-5,5-6,and 5-7 will usually require partial disassembly of

the supply in order to gain access to components (such as the series regulator transistors) that are not mounted on the main circuit board. If this is the case, refer as necessary to Paragraphs 5-65through 5-70 for disassembly procedures.

Table 5-4.Feedback Loop Isolation

STEP

 

 

 

ACTION

 

 

 

RESPONSE

 

 

 

PROBABLE CAUSE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

be

reset

by turning

 

supply off and then on.

 

 

NOTE: After each step, crowbar should

 

 

1

Inspect

LINE

circuit

breaker.

a.

Tripped.

 

 

 

a. Check rectifier, filter, and

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

triac for short. Faulty pre-

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

regulator. Procceed to Step

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3.

 

 

 

 

 

 

 

 

 

 

 

b.

Not

tripped;

 

 

 

b. Series regulator loop in

 

 

 

 

 

 

 

 

High

voltage

output.

 

 

high voltage

condition.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Proceed to Step 2.

 

 

 

 

 

 

 

c.

Not

tripped;

 

 

 

c.

Proceed to Step 2.

 

 

 

 

 

 

 

 

Low

voltage

output.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2

Inspect

overvoltage

lamp on

a.

On.

 

 

 

 

 

a.

Check

setting of

overvolt-

 

front pane 1.

 

 

 

 

 

 

 

 

 

 

age adjust (A5R125).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Check A4CR110 for short.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Series

regulator loop in

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

high voltage

condition.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Proceed to Step 3.

 

 

 

 

 

 

 

b.

Off;

 

 

 

 

 

b. Check setting of overvolt-

 

 

 

 

 

 

 

 

High voltage

output.

 

 

age adjust (A5R125).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Check A4CR110 for open,

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Q91 for open, Q92 for

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

short.

Series regulator

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

loop in high voltage con-

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

dition. Proceed to Step 3.

 

 

 

 

 

 

 

c.

off;

 

 

 

 

 

c.

Check

overvoltage adjust

 

 

 

 

 

 

 

 

Low

voltage

output.

 

 

(A5R125). Check A4CR110

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

for short. Check Q20 for

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

for short.

Proceed to Step

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3.

 

 

 

 

3

Isolate

fault

to either series

a.

Output

voltage

normal.

 

a. Check each series regula-

 

regulator

or

preregulator by

 

Variable from O volts

 

 

tor transistor

(A4Q103

 

using

the

following

steps:

 

to about 9 volts.

 

 

through A4Q108) for open.

 

(1) Open the gate lead to

 

 

 

 

 

 

 

 

Then

check

preregulator

 

 

 

 

 

 

 

 

 

by disconnecting

source

 

triac

A2CR1

by disconnect-

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

and proceeding to Table

 

ing either

end of resistor

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

5-7.

 

 

 

 

 

R88 (TP87 or TP88).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

b. Output

voltage

high.

 

b. High voltage condition in

 

(2)

Place a small dc pow-

 

 

er supply across the input

 

Varying

controls

has

 

 

series

regulator.

Proceed

 

capacitors (C 101 through

 

little

or

no effect.

 

 

to Table 5-5.Leave ex-

 

C104). A 0-10V, 2A sup-

 

 

 

 

 

 

 

 

ternal

source

connected.

 

ply is

sufficient.

 

c.

Output voltage

low,

 

c.

Low voltage

condition in

 

(3)

Set

external supply to

 

 

 

 

series

regulator

loop.

 

ten volts.

 

 

 

Varying

controls

has

 

 

 

 

 

 

little

or

no effect.

 

 

Proceed to Table 5-6.

 

(4)

Vary front panel volt-

 

 

 

 

 

 

 

 

 

 

 

 

Leave

external source

 

age

controls.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

connected.