Offset-Vernier Control-Voltage; Output Amplifier - HP 8112A Operating, Programming And Servicing Manual

Off set-vernier
Control-voltage

Output Amplifier

Caution
10.4-14 Servicing the Shaper and Output Amplifier
Check the offset-vernier control-voltage, received from the control
board A2 at board connector side of R501, against Table 10.4-6:
Table 10.4-6. Offset-vernier Control-voltages
HIL
-4.5 v -5.5 v
-7.9 V -8.0 V
Do not operate the HP 8112A without the heatsinks fitted on
n
board Al
If you need to replace one or more of the transistors Q505 - Q513,
n
do not attempt to remove the heatsink and
together, this is likely to damage the transistors.
1. Remove all the screws securing the heatsink(
2. Remove the heatsink(
3. Remove the adaptor(s) from the transistor(s) to be replaced.
4. Replace the transistor(s).
5. Re-fit the adaptor(s) and heatsink(
1. Set up the HP 8112A as follows:
RCL
output
2. Press the ISET) key
3. Measure the voltage at CR501 and CR502 (typ. 10 mV):
If it is fully negative (approximately -15 V) check U502, Q502,
Q504 and Q506.
If it is fully positive (approximately +15 V) check Q501, Q503,
Q505 and U502.
4. Check if Q510/Q511 or &512/Q513 have failed (emitter-collector
short-circuit).
If you need to change any of the output-stage transistors Q508 -
Q513, also check CR505 and CR506. They protect the output
stage at high amplitudes and frequencies by discharging the
base-emitter capacitor of Q510 -Q513.
5. Set the HP 8112A to FIXED mode, output ENABLED.
at R501 (typ)
-7.45 v
V +7.9 V
-4.8 V
V
transistor
0
- 1 v
Disabled
adaptors