TM 11-6625-2965-14&P

 

 

 

Table 5-3.

Overall

Troubleshooting

(Continued)

 

 

 

 

 

 

 

 

SYMPTOM

 

 

 

 

CHECKS AND PROBABLE CAUSES

 

 

 

 

 

 

 

 

 

 

b. Front

panel meter defective.

 

 

 

 

 

c . Series regulator feedback loop defective. Refer to Table 5-5.

 

 

 

 

 

 

 

 

Will

not current limit

a.

Q10 open. R81

defective.

 

 

 

 

 

 

 

 

 

 

 

High

ripple

a.

Check

operating

setup for

ground

loops.

 

 

 

b.

If output floating, connect lµf capacitor between output and ground.

 

 

 

c.

Ensure that supply is not crossing over to current limit mode under

 

 

 

 

loaded conditions.

 

 

 

 

 

 

 

 

 

 

 

 

 

Poor

line

regulation

a.

Check

reference

circuit

(Paragraph

5-55).

 

 

 

b. Check reference circuit adjustment (Paragraph 5-69).

 

 

 

 

 

 

 

Poor

load

regulation

a.

Measurement

technique.

(Paragraph 5-17)

(constant

voltage)

b. Check

reference circuit (Paragraph 5-55) and adjustment (Para-

 

 

 

 

 

 

 

graph 5-69).

 

 

 

 

 

 

 

 

 

c.

Ensure that supply is not going into current limit.

 

 

 

 

 

 

 

 

Oscillates

(constant

a.

Check

C5 for

open, adjustment

of

R30 (Paragraph 5-72).

 

voltage)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Poor stability

a.

Check

± 6.2Vdc

reference

voltages

(Paragraph 5-55).

(constant

voltage)

b.

Noisy

programming resistor

R10.

 

 

 

 

 

 

 

 

c .

CR1,

CR2 leaky.

 

 

 

 

 

 

 

d.

Check Rl, R12, R13, for noise or drift.

 

 

 

e.

Stage

Q1 defective.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

5-55 To check the zener diodes in the reference

circuit, proceed as follows:

 

 

a . Connect differential voltmeter across

zener

diode.

 

 

b.

Connect appropriate

load resistor, given

in Figure

5-4,across (+) and

(-) output terminals.

 

c . Turn VOLTAGE control fully clockwise.

 

d. Set METER switch to highest current

range

and

turn on supply.

 

 

e .

Adjust CURRENT controls until panel

meter reads exactly the maximum rated output cur- rent.

f.Read and record voltage indicated on dif- ferential voltmeter.

g.Short out load resistor by closing S1.

h.If reading on differential voltmeter dif- fers by more than 1.07mV for 6204B and 6205B or

.946mV for 6206B from the reading in Step f, re- place zener diode.

5-5b Series Regulating Feedback Loop. When troubleshooting the series regulating loop, it is useful to open the loop since measurements made anywhere within a closed loop may appear abnor- mal. With a loop closed, it is very difficult to separate cause from effect. As described in Tables 5-4and 5-5, the conduction or cutoff capability of each stage is checked by shorting or opening a previous stage, as follows:

1.Shorting the emitter to collector of a transistor simulates saturation, or the full ON condition.

2.Shorting the emitter to base of a transis- tor cuts it off, and simulates an open circuit be- tween emitter and collector.

5-57 Although a logical first choice might be to break the loop somewhere near its mid-point, and then perform successive subdividing test, it is

5-10