HP 6177B Operating And Service Manual page 33

Table 5-8. Troubleshooting Voltage Limit Circuit (Continued)
STEP
I
ACTION
I
RESPONSE PROBABLE CAUSE
I
I
I
Check turn-off of Q7 and
02- by
a. Output current rema Ins low,
I
c.
07, 08 shorted,
disconnecting collector of 06.
b. Output current increases. b. Reconnect collec-
tor and proceed to
I
Step 2.
2
I
Eliminate the turn-on circuit as a. Output current increases. a. CR40. C40 shorted,
c source
0:
trouble
by
discor:.-
b.
Output current rema ins l.ow. b.
Heconnect CR40
necting the anode of CR40.
ana proceed to
Step 3.
I
3
ChecK turn-off of Q6 by shorting
a. Output current remains low,
a. 06 shorted.
05 emitter-to-colle ctOf,
b.
Output current increases.
D.
Remove short and
I
!
I
proceed to Step
4.
4
ChecK turn-on of QS by shorting a. Output current remains low. a. 05 open.
Q4- emitter-to-collector.
b. Output current increa ses.
b. Remove short and
proceed to Step
5.
5 Check tum-on of 04
by
opening
a. Output current rema ins low.
a.
02, 04 open, R81
VR2 near the consta nt current shorted. Open
source. strap between AS
and A6,
b.
Output current in crea s e s, b. VR2 shorted.
Check R5 and R6
for open,
Table 5-9. Troubleshooting the Guard Circuit
STEP
ACTION
RESPONSE PROBABLE CAUSE
PART
A.
UNIT LOCKED-UP
1
Check the operation of 22
by
a. Output current decreases. a. 22 defective.
switchir.g 21 and 22.
b.
Output current remains high.
b. Proceed to Step 2.
2 Check operation of Q18 by open-
a.
Output current remains high.
a.
018A open. 018E
ing strap between terminal Al shorted. CR15,
and A2. CR16 shorted.
b.
Output current decreases. b. R40 shorted.
R37
open,
PART
Jl.
UNIT LOCKED-DOWN
1
Check operation of 22 by switch-
a.
Output current increases,
a. 22 defective.
ing Z 1 and Z2.
b. Output current rema ins low.
b.
Proceed to Step 2.
2 Check operation of 018 by short- a. Output current rema ins low. a. 018 shorted. 021,
ing AO to A!. VRIO open.
b. Output current decreases.
b. R40 open. R36
shorted.
5-13