Table 5-3.

Overall Troubleshooting (Continued)

TM 11-6625-2958-14&P

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SYMPTOM

 

 

 

 

 

 

 

PROBABLE CAUSE

 

 

 

 

 

 

 

 

High

ripple

(continued)

 

 

current comparator circuit (Z1 and associated components).

 

 

 

 

 

Poor

line regulation

 

a.

Improper measurement technique. Refer to Paragraph 5-13.

 

 

 

 

b. Incorrect

reference

and/or

bias

voltages. Refer

to

Table

 

 

 

 

 

5-2.

 

 

 

 

 

 

 

 

 

 

 

 

 

Poor load regulation

 

a.

Improper measurement technique. Refer to Paragraph 5-11.

(Constant

voltage)

 

b. Incorrect

reference

and/or

bias

voltages. Refer

to

Table

 

 

 

 

 

 

 

 

 

5-2.

 

 

 

 

 

 

 

 

 

 

 

 

 

c.

Supply

current limiting.

Check

constant current

compara-

 

 

 

 

 

tor circuit (Z1 and associated components).

 

 

 

 

 

 

Poor load regulation

 

a.

Improper measurement technique. Refer to Paragraph 5-44.

(Constant

current)

 

b. Incorrect

reference

and/or

bias

voltages. Refer

to

Table

 

 

 

 

 

 

 

 

 

5-2.

 

 

 

 

 

 

 

 

 

 

 

 

 

c. Supply

voltage limiting. Check

constant voltage

compa-

 

 

 

 

 

rator circuit (Z1 and associated components) and voltage

 

 

 

 

 

clamp

circuit,

Q1.

 

 

 

 

 

 

 

 

 

d. Leaky

C19,

A3C3.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Oscillates

 

a. Adjustment

of

R47.

Refer to Paragraph 5-99.

 

 

(Constant

current\constant

voltage)

b. Faulty C40, C41, C19, A3C3, R50.

 

 

 

 

 

 

 

 

 

 

 

 

c. Open sensing Iead (+S).

 

 

 

 

 

 

 

 

 

 

 

 

Instability

 

a.

Incorrect reference and/or bias voltages; CR92 defective.

(Constant

current/constant

voltage)

 

Refer to Table 5-2.

 

 

 

 

 

 

 

 

 

b. Noisy voltage

or current controls

(A5R121, A5R122, or

 

 

 

 

 

A5R123, A5R124); noisy VR60 or VR61.

 

 

 

 

 

 

c.

Integrated

circuit Z1 defective.

 

 

 

 

 

 

 

d. CR4, CR5, CR6, or CR21 leaky.

 

 

 

 

 

 

 

e. R2, R3, R4, R5, R6, R22, R30, R31, C2 noisy or drifting.

 

 

 

 

Cannot reach maximum output

a.

Q20 shorted.

One or more of series regulator transistors

 

 

 

 

 

(A4Q103 through A4Q108) open,

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

5-58 Table 5-3contains symptoms and probable causes of many possible troubles. If either high or low output voltage is a symptom, Table 5-4contains the steps necessary to isolate the trouble to one of the feedback loops and instructions directing the tester to the proper table for further iso- lation. Because of the interaction between feedback loops, it is necessary to refer to Table 5-4before proceeding to Tables 5-5,5-6,or 5-7.

5-59 Tables 5-5,5-6,and 5-7contain troubleshooting methods for the series regulator and pre- regulator feedback loops once the fault has been

isolated to either one. Tables 5-5and 5-6contain instructions for driving each stage of the series regulator feedback loop into conduction or cut-off. By following the steps in these tables, the fault can be isolated to a circuit or to a com- ponent.

5-60 Table 5-7contains troubleshooting procedures for the preregulator feedback loop. The troubleshooting method is based upon comparing the waveforms shown in Figure 7-9with those actually found at the various test points in the pre- regulator control circuit. As indicated in Table

5-11