HP 8112A Operating, Programming And Servicing Manual page 267

Troubleshooting
Note
Output Address
Decoder
a key, ( LCL) for example, to return the microprocessor to normal
•
If an error code is being displayed by the HP 8 1 12A you must press
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
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
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 Mnemonic
pin
1
2
3
4 & 5
9
10
11
(
See Chapter 10.7) to position Pl.
A3 µP Board
Connections
TP "SA"
TP "SP"
TP "E"
Description
LA3
Sub decoded address
LA4
Sub decoded address
LA5
Sub decoded address
WS5 Sub decoded address
LBC
Load Burst Counter
HBB
High Byte Burst
LBB Low Byte Burst
Servicing the Burst Control Circuit 1 0.6-5
Free run
Signature
P50H
CH9U
8759
8U95
OF4F
71PO
58F8