HP 6259B Operating And Service Manual page 44

Table 5-3. Overall Troubleshooting (Continued)
SYMPTOM
PROBABLE CAUSE
High ripple
a. Ground loops in operating setup. Refer to paragraph 5-17.
b. Incorrect reference or bias voltages. Refer to Table 5-2.
c. Supply crossing over to constant-current operation under loaded conditions.
Check current limit setting or constant-current comparator circuit (21 and
associated components).
Poor line regulation
a. Improper measurement technique. Refer to paragraph 5-13.
b. Incorrect reference or bias voltages. Refer to Table 5-2.
Poor load regulation
(Constant-voltage)
a. Improper measurement technique. Refer to paragraph 5-11.
b. Incorrect reference or bias voltages. Refer to Table 5-2.
c. Supply current limiting. Check constant-current comparator circuit
<Z1 and associated components).
Poor load regulation
(Constant-current)
a. Incorrect reference or bias voltages. Refer to Table 5-2.
b. Supply voltage limiting. Check constant-voltage comparator circuit
(Z1 and associated components) and voltage clamp circuit Q1.
c. Leaky Cl9, A3C3.
d. CR92 defective.
Oscillates
(Constant-current or
constant-voltage)
a. Adjustment of R47. Refer to paragraph 5-98.
b. Faulty C40, C41. Cl9, A3C3, R50.
c. Open sensing lead (+S).
Instability
(Constant-current/
constant-voltage)
a. Incorrect reference or bias voltages; CR92 defective. Refer to Table 5-2.
b. Noisy voltage or current controls (A5R1 21, A5R122, or A5R123, A5R1 24);
noisy VR60 or VR61.
c. Integrated circuit Z1 defective.
d. CR4, CR5, CR6, or CR21 leaky.
e. R3, R4, R5, R6, R22, R30, R31, C2 noisy or drifting.
Cannot reach maximum output
Q20 shorted. One or more series regulator transistors (A4Q103 thru
A4Q110) open.
Table 5-4. Feedback Loop Isolation
STEP
ACTION RESPONSE
PROBABLE CAUSE
-1--
NOTE: After each step, reset crowbar by turning supply off then on.
i i
1
Inspect LINE circuit breaker. a. Breaker tripped.
b. Breaker OK; output
voltage high.
c. Breaker OK; output
voltage low.
a. Check rectifier, filter, and triac for
short. Proceed to step 3.
b. Proceed to step 2.
c. Proceed to step 2.