HP 8112A Operating, Programming And Servicing Manual page 285

Troubleshooting
Note
Free Running Signature
Analysis
Note
Address Bus
•
If an error code is being displayed by the HP 8 1 1 2A you must press
a key, for example, t o return the microprocessor t o normal
operation before troubleshooting.
•
The component layouts and locators for the microprocessor board
A3, the keyboard A4 and the display board A5 are at the end of
the chapter.
To carry out signature analysis the microprocessor must be set to
a free-running routine in which it increments through all addresses
continuously. To set the microprocessor to free-run:
1 . Move the jumper on J4 to the free-run position.
2. Disconnect the W4, (the cable to the Control Board) to force NMI
high.
3. Reset the microprocessor by shorting TP RES to ground (the pin
beside TP RES) for a short time
When you have finished testing, return the jumper on J4 to its
normal position and reconnect W4.
The address bus drivers and decoders can be checked using signature
analysis.
1. Set the microprocessor to free-run as described in "Free Running
Signature Analysis" and connect the signature analyzer probes as
given in Table 1 0.7-2.
Table 1 O.7-2. Signature Analyzer Probe connections
2. Verify the reading at microprocessor +5 V supply is is 0003. If it
is not , the microprocessor is not free-running.
3. Use the data probe to check the signatures given in Table 1 0.7-3:
Servicing the Microprocessor and Front-panel 1 o.7 - 1 5
Probe Trigger Connect to
Start
f TP "SA"
f
Stop
TP "SP"
\
Clock
TP "E"
Ground
Ground