TROUBLESHOOTING
e. Remove the four screws that hold the in-
ner and outer component board bracket to the
a. Remove the top cover from the unit.
center chassis assembly (fig. 5-1).
b. Remove the rear terminal strip from the
f. Lay the component board assembly to the
heat sink assembly and lay it to one side (to
side of the cabinet as far as the cable harness
clear the heat sink).
will allow it to go.
c. Remove the four mounting screws that
hold the center chassis assembly to the cabi-
Note: The above procedure will permit the main-
net (fig. 5-1).
tenance man to have access to the various test points
d. Carefully raise the center chassis assem-
called out by the troubleshooting instructions, as well
bly and slide the heat sink assembly to the
as by the inspection standards outlined in paragraphs
rear of the unit as far as the cable harness
will allow.
Symptom
Probable cause
Procedure
1. No output to load (COARSE ADJ. Fuse F1 blown . . . . . . . . . . . . . . . .
Replace fuse F1.
control at max clockwise).
2. No output to load (meter M1 at Fuse F2 blown . . . . . . . . . . . . . . . . .
Replace fuse F2.
zero and meter M2 reading nega-
tive).
3. Low output (less than 36 volts Transistor Q13 or Q14 shorted.
Replace transistors with same type.
with COARSE ADJ. control
Check resistors R17 and R19 for
completely clockwise).
overheating.
Replace Zener diode with same type
Low Zener diode voltage (CR4).
and rating.
Adjust as described in paragraph
Improper alignment of reference
supply. Voltage across capacitor
and secondaries of transformers
C1 is low.
T1, T2, and T3. Check rectifiers
CR1 and CR2.
4. Incorrect output range (para 5-3). Reference supply faulty . . . . . . . .
Check all transistors (Q16, Q17, Q18,
Q19, Q20, and Q21) and Zener
diode CR12.
Follow adjustment procedures (para
Shaft coupling on ganged T1 and
R30 loose.
Remove transistors Q12, Q13, Q18,
High output (over 36 volts dc when Passing transistor shorted (Q1, Q2,
and Q19 from their sockets.
Q3, Q4, Q5, or Q6) or over-
COARSE ADJ. control is max
a. If output voltage does not fall,
loaded.
clockwise).
check passing stages.
b. If output voltage does fall, check
control amplifiers Q12, Q13,
Q14, and Q15.
5. High output with resistor R13 Transistor Q10 shorted . . . . . . . . .
Replace transistor.
overheating. (Feel for heat).
Replace transistor.
6. High output with resistor R14 over- Transistor Q11 shorted . . . . . . . . . .
7. High output with resistors R16 Transistor Q12 shorted . . . . . . . . .
Replace transistor.
and R17 overheating.
Replace transistor.
8. High output with resistors R20 Shorted transistor Q15 . . . . . . . . . .
and R19 overheating.
5-1
