Table 5-2. Miscellaneous Troubles
SYMPTOM CHECK - PROBABLE CAUSE
High ripple a. Check operating setup for ground loops (see paragraph 5-22).
b. Check main rectifiers (CR11, CR12, CR31, CR32, CR51, CR52)
for open.
c. Supply may be operating in current limit mode. Check current
limit adjustment, paragraph 5-26, steps (l) thru (t).
Will not current limit Check for open OR-gate diodes (CR5, CR25, CR45) or defective
current limit amplifier (U1, U2, U3).
Poor load or line regulation a. Check bias and reference voltages, Table 5-4.
b. Check main rectifiers and filters for opens.
Oscillation or poor transient a. High frequency oscillations (above 50 kHz) can be caused by an
recovery time open C4, C14, or C24.
b. A defective output capacitor (C1, C11, or C21) can cause
oscillations in one of many frequency ranges.
c. Oscillation only in the current limiting mode can be caused
by an open C3, C13, or C23.
Transient voltage overshoot a. Overshoot only in the -20V supply can be caused by a
at turn-on or turn-off. shorted Q13.
b. Overshoot in all three supply outputs can be caused by an
open Q14 or a shorted Q15.
Table 5-3. Initial Troubleshooting Procedure
STEP ACTION RESPONSE NEXT ACTION
1 Check output voltage of +20V a. Normal a. Proceed to step (2).
supply.
b. Zero volts b. Check ac line fuse (F1). If blown, proceed
to paragraph 5-38. If not blown, check
bias and reference voltages (Table 5-4).
c. Output voltage lower c. Check bias and reference voltages
or higher than rating. (Table 5-4).
2 Check output voltage of -20V a. Normal a. If +20V and -20V outputs are both
supply in fixed tracking ratio normal with no load, a supply might
mode. be current limiting under load. To check
this adjustment see paragraph 5-16,
steps (l) thru (p).
b. High, low, or zero b. Proceed to -20V supply troubleshooting,
output voltage. Table 5-6.
5-7
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