HP 437B - SINGLE ERROR CODES AND TROUBLESHOOTING SUGGESTIONS (CONT.)

HP 437B
Service Sheet BD1
Table
8-5.
Single
Error
Codes
and
Troubleshooting
Suggestions
(Cont.)
8-26 SFRVICF
Troubleshooting Suggestions
Keyboard/Display controller failure (A3U25 or A3U26).
Verify
TTL
signals
at
A3U25
pins
19
and
39.
If
not
present,
replace
A3U25,
If
present,
verify
a
TTL
signal
at
A3U26
pin
15.
If
not
present,
replace A3U26.
Keyboard data failure (A3U25 or A3U26).
Check
for
a
pulse
at
A3U26
pin
8
when
pressing
a
key.
If
a
pulse
is
not
present, press all keys consecutively while checking for a pulse.
If
none
of
the
keys
pressed
creates
a
pulse
at
A3U26
pin
8,
replace
A3U26.
If
error
7!
persists,
replace
A3U25.
Data line to A3U26 is open. Check data bus from A3U25 to A3U26
(KD0-KD7) or replace the Digital board.
Keyboard/Display controller self-test failure (A3U26).
Replace A3U26.
Display not responding.
Ensure display cable (at A3J8) is connected. Verify TTL signals at
A3U26 pins 13, 14. If the display cable is connected and TTL signals
are present, replace the display.
Digital failure at A3J6.
Disconnect ribbon cable W6 at A3J6. Set LINE switch to STBY,
then ON. If error code 75 persists, replace A3U24 (and A3U28 if necessary).
If the error code is not repeated, the problem is on the Analog board.
One of the Analog board components connected to the following data lines
is preventing normal operation.
ADO - AD7
AAO - AA2
NADS
STRAMP
Turn to Service Sheets A4a, b, or c to troubleshoot the Analog board.