Common Troubles - HP BENCH Series Operating And Service Manual

1. First, the reference, bias, and filtered
dc voltages as given in Table 5-3 should be check
ed. Then the voltage levels at critical points
(base and collector) in the feedback loop should
be measured and compared to the normal voltages
given on the overall schematic diagram at the rear
of the manual. This method of troubleshooting a
feedback loop is not always conclusive; a better
method is described in (2).
2. First, measure the reference, bias, and
filtered dc voltages as given in Table 5-3. Then,
drive each stage in the feedback loop into conduc
tion or cutoff by either shorting or opening the pre
vious stage as indicated in Tables 5-4 or 5-5.
Table 5-2. Common Troubles
SYMPTOM
PROBABLE CAUSE
Low output or no output voltage Refer to Table 5-3, then 5-4.
High output voltage Refer to Table 5-3, then 5-5.
High ripple
a. Check operating setup for ground, refer to Paragraph 5-22.
b. If output floating, connect l[if capacitor between output and
ground.
c. Check for excessive internal ripple; refer to Table 5-3.
d. Ensure that supply is not in current limit operation under
loaded conditions. To prevent this condition, increase load
resistance so that output current does not exceed maximum
rated output.
e. Check for low voltage across C5 or C9.
Poor line regulation a. Improper measuring technique; refer to Paragraph 5-6.
b. Check reference circuit voltages, Table 5-3.
Poor load regulation
(Constant Voltage)
a. Improper measuring technique; refer to Paragraph 5-6.
b. Check reference circuit voltages (Table 5-3).
c. Ensure that supply is not in current limit operation under loaded
conditions. To prevent this condition, ensure that output cur
rent does not exceed maximum rated output.
Oscillates
a. Check C3 and RI7.
Poor stability
(Constant Voltage)
a. Check +6.2Vdc reference voltage (Table 5-3).
b. Noisy programming resistor RIO or RIl.
c. CRl, CR2 leaky.
d. Check Rl, R12, and C1 for noise or drift.
e. Stage 01/Q2 defective.
Poor transient recovery
a. Check RI7 and C3.
5-9