HP 6960A - 5-11 Troubleshooting

Model 6960 A
5-11 Troubleshooting
Section V
5-12 Components within Hewlett-Packard instruments are conservatively aperated to
pravide maximum instrument reliability. In spite of this, parts within an instrument
may fail. In this case a systematic approach can greatly simplify and thereby speed
up the repair.
CAUTION
Be careful nat to short voltages across the transistors, small bias
changes may ruin a transistor due to excessive dissipation. Be
sure to turn the instrument off before doing any soldering.
If there is no voltage throughout the instrument check the fuse and primary trans-
former circuit. Transistors Oland 0 2 should have a voltage drap af about 5 to
6 V across them. If the pilot lamp is an but the de output shows no '!olhge or
excessive voltoge with high ripple check all voltages produced by the auxiliary
and reference voltage supply. These voltages should be at ratings sho.,,' in the
schematic diagram and should not exhibit significant changes while varying the
input line voltage. If all of these voltages are operating properlY ,i'e Trouble lies.
in the amplifier loop. Check each transistor of the amplifier, ;ncl·.~;cg fhe diodes
CR 13 and CR 14 as well as the front panel potentiometer R 40 (VOLTAGE ADJUST).
Some symptoms indicate, with high degree af probability that certain components
may be faulty. Refer to the trouble localization chart belaw.
Table 5-2 Trouble Localisation chart
Symptom
Blown Line fuse
Either 18 V or 36 V range
on Iy is working proper Iy
Excessive short circuit current
Poor current limiting.
Poor stability of output voltage
Poar load regulation
Poor line regulation
Check
Primary circuit of T 1
T 1
itself, CR 1 to CR 10
CltoC3.
Push button sw itch
R 7, R 10, R 39 AB, 0 5
CR 20, CR 21, R 40
08,07, CR 14,03
CR21, 06, 04
After replacing faulty components carry out the performance test according to para-
graph 5-7 and, if necessary, the adjustment procedure according to paragraph 5-9.
5-8