HP 8112A, Operating, Programming And Servicing Manual

Page: 267 / 406

Troubleshooting
Note
Output Address
Decoder
•
If an error code is being displayed by the HP 81 12A you must press
a key, for example, to return the microprocessor to normal
operation before troubleshooting.
11
The component layout and locator for the burst control part of
board
A2 is the same as Figure 10.5-6.
Address decoder Ul6 provides control signals for the burst control
circuits. These can be checked using signature analysis:
1 . Set the microprocessor to free run mode as follows:
a. Set the P l wire on board A3
(
See Chapter 10.7) to position
P l .
b. Disconnect Jumper A2W l .
c . Connect RES o n A 3 to ground for a short time t o ensure the
microprocessor is reset.
d. Connect the signature analyser ground to the Control Board
ground and connect the probes as follows:
Sig. Analyser
Start
f
Stop
/
Clock
"\.
A3 µP Board
Connections
TP "SA"
TP "SP"
TP "E"
e. Verify that the reading at the Microprocessor +5 V is 0003. If
it is not, then the microprocessor is not free running.
f. Check the signatures of U16 against those given in Table 10.6-1
Table 1 0.6-1 . Output Address Decoder Signatures
U16
pin
1
2
3
4 & 5
9
10
11
Mnemonic Description
Free run
LA3
LA4
LA5
WS5
LBC
HBB
LBB
Signature
Sub decoded address
P50H
Sub decoded address
CH9U
Sub decoded address
8759
Sub decoded address
8U95
Load Burst Counter
OF4F
High Byte Burst
71PO
Low Byte Burst 58F8
Servicing the Burst Control Circuit 1 0.6-5