HP BENCH Series - Table 5-5 High Output Voltage Troubleshooting; 5-53 Repair and Replacement

Table 5-5. High Output Voltage Troubleshooting
STEP
ACTION
RESPONSE
PROBABI^ CAUSE
1
Turn the VOLTAGE control to ap
proximately mid-range and dis
connect the load. If the output
voltage should rise to an exces
sive value during the following
procedures, the VOLTAGE control
could be damaged if it is turned
fully GCW.
2
Check turnoff of Q7 by shorting
Q5 emitter to collector
a. Output remains high
b. Output decreases
a. Q7, CR7, R20 defective.
b. Remove short across
Q5 and proceed to
Step 3.
Check conduction of Q5 by '
removing Q4 collector lead
a. Output remains high
b. Output decreases
a. Stage Q5 defective.
b. Replace Q4 collector
lead and proceed to
Step 4.
4
Check turnoff of Q4 by shorting
QI emitter to collector
a. Output remains high
b. Output decreases
a. Stage Q4 defective
b. Sta ge Q1/Q2 defective.
Check RI0,RI1 for open
and RI2 for short.
5-53 REPAIR AND REPLACEMENT
5-54 Before servicing a printed wiring board, refer
to Figure 5-11. Section VI of this manual contains
a tabular list of the instruments replaceable parts.
Before replacing a semiconductor device, refer to
Table 5-6 which lists the special characteristics
of selected semiconductors. If the device to be
replaced is not listed in Table 5-6, the standard
manufacturers part number listed in Section VI is
applicable.
Table 5-6. Selected Semiconductor Characteristics
REFERENCE
DESIGNATOR
CHARACTERISTICS ($ PART NO.
SUGGESTED
REPLACEMENT
Q7 Power NPN Silicon hfe =35 min. @ I =4 Ampere
VcE = 4 Volts.
1854-0225 2N3055 R.C.A.
5-11