HP 6236A Operating And Service Manual page 24

Table 5-6. -20V Supply Troubleshooting (Continued)
SYMPTOM
STEP - ACTION
RESPONSE - PROBABLE CAUSE
3. Measure voltage at TP14.
a. If TP14 is approx. -O.7V, check for open CR26
or defective U2.
b. If TP14 is approx. +0.7V, check Z1 for open from
pin 7 to 12 or for short from pin 6 to 1~.
Low output voltage 1. Measure voltage at TP5.
a. If voltage at TP5 is zero or positive, check for open
(more than 1 % lower
Q3, Q13, or R34, and defective Q4.
than +20V supply)
b. If TP5 voltage is approx. -0.7V, proceed to step
(2).
2. Measure voltage at TP9.
a. If TP9 is negative, check for open Z1 between
pins 5 and 15, open R28, and defective R26 or U2.
b. If TP9 is approx. +0.7V, proceed to step (3).
3. Measure voltage at TP10.
a. If TP10 is approx. -0.7V, check CR26 for short.
b. If TP10 is -1.0 to -1.4V, proceed to step (4).
4. Measure voltage at TP14. a. If TP14 is approx. +0.7V, replace U2.
b. If TP14 is zero volts, check for shorted CR22 or
CR23.
c. If TP14 is approx. -0.7V, check
~1
for open
between pins 6 and 12 or short between pins 7 and
12, and check for leaky or shorted C12.
Table 5-7. +6V or +18V Supply Troubleshooting
SYMPTOM STEP - ACTION RESPONSE - PROBABLE CAUSE
.
High output voltage 1. Attempt to turn down loop
a. If output voltage remains high, check Q7, Q15,
(higher than rating)
by shorting Q15 emitter-to-base.
and CR49 for short.
b. If output voltage falls to near zero, remove short
from Q15 and proceed to step (2).
2. Measure voltage at output a. If TP6 is approx. -0.7V, check for open CR46 or
of OR-gate (TP6).
R41, and defective U3.
b. If TP6 is approx. +0. 7V, check for defective Q8.
Low output voltage 1. Measure voltage at output
a. If TP6 is between zero and -0. 7V, check for open
(lower than rating)
of OR-gate (TP6). Q7, Q15, R54, or CR59, and defective Q8.
b. If TP6 is approx. +0.7V, proceed to step (2).
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