Troubleshooting
Note
Timer
•
If an error code is being displayed by the HP 81 12A you must press
a key,
for example, t o return the microprocessor to normal
operation before troubleshooting.
•
The component layout and locator for the standard control board
A2 is at the end of the chapter.
Verify the following voltages:
•
DAC supply U9 pin 2: +5 V
•
DAC reference TP9: - 1 V
•
DAC reference TP8: -9 V
1 . Set up the HP 81 12A as follows:
RCL
PER
0
10 µs
2. Check that pin 3 of U26 is delivering a signal of approximately
100 Hz.
Address Decoders
The address decoders can be checked using signature analysis:
1. Set the microprocessor to free run mode as follows:
a. Set the Pl wire on board A3
(
See Chapter 10.7
)
to position
P l .
b. Disconnect Jumper A2Wl.
c. Connect RES on A3 to ground for a short time to ensure the
microprocessor is reset.
d. Connect the signature analyser ground to the Control Board
ground and connect the probes as follows:
Sig. Analyser A3 µP Board
Start
.f
Stop
.r
Clock
\
Connections
TP "SA"
TP "SP"
TP "E"
e. Verify that the reading at the Micropro5 V is 0003. If
it is not, then the microprocessor is not free running.
f. Check the signatures of U l , U15 and U16 against those given
in Table 10.5- 1
Servicing the Control Board 1 0.5-1 1
Summary of Contents for 8112A
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Page 295: ...MP MP3 MP MP2 MP4 MPS MP 1 2 MPS MP MP I B ElElElEl Replaceable Parts A 3 ...
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