TM 11-6625-2958-14&P

5-56OVERALL TROUBLESHOOTING PROCEDURE

5-57 To locate the cause of trouble, follow Steps 1, 2, and 3 in sequence:

(1)Check for obvious troubles such as trip- ped circuit breaker, defective power cord, incor- rectly strapped rear terminals, input power failure or defective meter. Next, remove the top and bot- tom covers and inspect for open connections, charred components, etc. , paying particular atten- tion to both sides of the main circuit board. (Refer to Paragraph 5-64for the main circuit board remov-

al procedure. ) If the trouble source cannot be detected by visual inspection, re-install the main circuit board and proceed to Step (2).

(2)In almost all cases, the trouble can be caused by incorrect dc bias or reference voltages; thus, it is a good practice to check the voltages in Table 5-2before proceeding with Step (3). Re- fer to Figure 7-10 for the location of the test points listed in Table 5-2.

(3)Disconnect load and examine Table 5-3to determine your symptom and its probable cause.

 

 

 

 

Table

5-2.Reference and Bias Voltages

 

 

 

(Refer to Schematic and Figure 7-10 for test point locations)

 

 

 

 

 

 

 

 

 

STEP

 

METER

 

METER

 

NORMAL

NORMAL

PROBABLE CAUSE

 

COMMON

 

POSITIVE

 

VDC

RIPPLE (P-P)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1

 

+S

 

TP63

 

+12.4 ± 7%

2.0mV

CR61, CR62, Q60, Q61, Q62,

 

 

 

 

 

 

 

 

Q63

 

 

 

 

 

 

 

 

 

2

 

+S

 

TP64

 

+6.2 ±5%

0.5mV

VR60, VR61, Q62, Q63

 

 

 

 

 

 

 

 

 

 

3

 

+S

 

TP65

 

-6.2 ± 5 %

2.0mV

VR60, VR61, Q62, Q63

 

 

 

 

 

 

 

 

 

4

 

+S

 

TP66

 

+11 ±15%

2.0V

C44, CR53, CR54

 

 

 

 

 

 

 

 

 

5

 

+S

 

TP67

 

-4.0± 1 2 . 5 %

0.8V

C44, CR53, CR54, CR45, CR46,

 

 

 

 

 

 

 

 

CR47, CR48, CR49

 

 

 

 

 

 

 

 

 

6

 

+S

 

TP68

 

-2.4±12.5%

0.4V

CR54, CR45, CR46, CR47,

 

 

 

 

 

 

 

 

CR48, CR49

 

 

 

 

 

 

 

 

 

 

 

Table 5-3.

Overall Trouble shooting

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SYMPTOM

 

 

 

 

 

 

PROBABLE CAUSE

 

 

 

 

 

 

 

 

 

 

 

 

Low or no output voltage

 

a.

Front panel

meter

defective.

 

 

(Overvoltage lamp may be on or off)

b. Crowbar

not

reset

or defective. Refer to Table

5-4.

.

 

 

 

 

 

 

 

c.

Series regulator or preregulator feedback loop defective.

 

 

 

 

 

Refer to Table 5-4.

 

 

 

 

 

 

 

 

 

 

 

 

 

High

output voltage

 

a.

Front panel

meter

defective.

 

 

 

 

 

b. Open circuit between sensing terminals (*S) and output ter-

 

 

 

 

 

minals

(*OUT).

Refer to Table 5-4.

 

 

 

 

 

c.

Series regulator or preregulator loop defective. If crowbar

 

 

 

 

 

does not trip, it also is faulty. Refer to Table

5-4.

 

 

 

 

 

 

 

 

 

 

High

ripple

 

a.

Ground

loops in

operating

setup. Refer to Paragraph 5-15.

 

 

 

 

b. Incorrect

reference

and\or

bias voltages. Refer

to Table

 

 

 

 

 

5-2.

 

 

 

 

 

 

 

 

 

 

c.

Supply crossing over to constant current operation under

 

 

 

 

 

loaded

conditions.

Check

current limit setting

or constant