Xerox Phaser 8400 Service Manual page 206

Electronics Troubleshooting Guide
If the PE and PS indicators do not flash,
the short is on the I/O board or related
cabling. Skip the rest of this section if the
PE and PS indicators flash because the
problem is elsewhere in the printer.
Verify short is on the I/O board by using
an ohmmeter to check the resistance on
J270, pin 1 to ground. Resistance of less
than 1K ohm indicates a problem.
To isolate problem to I/O board or related
cabling, unplug I/O board connectors:
1) Umbilical Right ('A' / J1)
2) Waste Tray Sense ('B' / J110)
3) Stripper Solenoid ('D' / J250)
4) Paper Tray Sense ('E' / J610)
5) Front Door Sense ('F' / J600)
6) Inkload Signal ('H' / J910)
7) DMU Sense ('J' / J860)
8) Drum Thermistor ('K' / J870)
9) Exit Module ('L' / J680)
10) Heater Relay Control ('G' / J950)
Retest the resistance of the I/O board. If
the resistance is still less than 1K ohm,
replace the I/O board, reinstall all cables
and retest printer.
If the I/O board resistance is OK, plug in
the I/O board connectors one at a time
and retest the resistance
Plug in all cables removed during service
Attach printer covers
Perform full test of printer
Short circuit REQUIRED: Follow all procedures from
on 3.3V 'Short circuit on 3.3V power supply within
power the Electronics Module' and 'Short circuit
supply on 3.3V power supply within the I/O
within the board' before proceding
Control
Panel
General Troubleshooting
* Possible solution to
problem *
Trace through all
service steps
performed to
reattach any cables
that were unplugged
during debugging
Following the
suggested debug
procedures in the
specified sequence
generally provides
better test coverage
than performing tests
in a different order
4-61