5-47 To check the output stability, proceed as follows:

a.Connect test setup shown in Figure 5-5.

b.Turn CURRENT controls fully clockwise and adjust VOLTAGE controls for 40Vdc output.

c. Allow 30 minutes warm-up then record the differential voltmeter indication.

d.Mter 8 hours, differential voltmeter should change by less than 45mV from indication recorded in Step c.

5-48 TROUBLESHOOTING

5-49 Before attempting to troubleshoot this in- strument, ensure that the fault is with the instrument and not with an associated circuit. The performance test (Paragraph 5-10)enables this to be determined without having to remove the instrument from the cabinet.

5-50 A gcod understanding of the principles of operation is a helpful aid in troubleshooting, and it is recommended that the reader review Section IV of the manua~ before attempting to troubleshoot the unit in detail. Once the principles of operation are understood, refer to the overall troubleshooting procedures in Paragraph 5-53to locate the symptom and probable cause.

5-51 The schematic diagram at the rear of the manual (Figure 7-1) contains normal voltage read-

TM 11-6625-2965-14&P

ings taken at various points within the circuits. These voltages are positioned adjacent to the applicable test points (identified by encircled num- bers). Component and test point designations are marked directly on the main printed wiring board.

5-52 If a defective component is located, replace it and re-conduct the performance test. When a component is replaced, refer to the repair and replacements and adjustment and calibration paragraphs in this section.

5-53 OVERALL TROUBLESHOOTING PROCEDURE

5-54 To locate the cause of trouble follow Steps 1, 2, and 3 in sequence.

(1) Check for obvious troubles such as open fuse, defective power cord, input power fail- ure, or defective voltage or current meter. Next remove the top cover (held by four retaining screws) and inspect for open connections, charred components, etc. If the trouble source cannot be detected by visual inspection, proceed with Step 2.

(2)In almost all cases, the trouble can be caused by improper dc bias or reference voltages; thus, it is a good practice to check voltages in Table 5-2,before proceeding with Step 3.

(3)Disconnect the load and examine Table

5-3to determine your symptom and probable cause.

Table 5-2. Reference Circuit Troubleshooting

STEP

METER

METER

NORMAL

NORMAL

 

 

RIPPLE

IF INDICATION ABNORMAL, TAKE THIS ACTION

COMMON

POSITIVE

INDICATION

 

(P-P)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1

+s

33

6.2

*

0.3Vdc

. 3mV

Check 12.4

Volt bias or VR1 (See next paragraph)

 

 

 

 

 

 

 

 

2

31

+s

6.2

+ 0.3Vdc

. 4mV

Check 12.4

Volt bias or VR2 (See next paragraph)

 

 

 

 

 

 

 

3

+s

37

12.4

*1. OVdc

2.8KV

Check Q8, Q9, CR22, CR23, C1O, T1

 

 

 

 

 

 

 

 

4

38

41

7.5

*

.7Vdc

lV

Check C12, CR8, CR24, CR25

 

 

 

 

 

 

 

 

 

Table 5-3. Overall Trouble shooting

v

SYMPTOM

 

 

 

CHECKS AND PROBABLE CAUSES

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

High

output

voltage

a.

Front

panel

meter defective.

 

 

 

 

b. Series regulator feedback loop defective. Refer to Table 5-4.

 

 

 

 

 

 

 

 

 

Low

output

voltage

a .

Fuses

blown

(Check CR26-CR29 or C14 for short).

 

 

 

 

 

 

 

 

 

5-9