IBM 3112 Service Manual page 34

If the duplexer does not home immediately but homes after 5 or 6 sec-
onds, the duplexer is receiving +34VDC from the printer but is not com-
municating with the printer. The duplexer homes on its own as a signal
that it is functional.
If the duplexer does not home at all, it is either damaged or is not
receiving +34VDC from the printer.
To check the connection from the printer engine board to the duplex
system board, remove the printer RIP Board. Remove the duplex top
cover and table cover, and reinstall the duplexer. Engine board J3-2
should have continuity with the duplex system board J5-1, J3-3 with J5-
2, and so on. With power on, you should have the following voltages:
Connector
Engine Board
Duplex System
Board
If you do not find a cable or voltage problem replace the duplex system
board. If this does not fix the problem, replace the printer engine board.
A 933 error indicates that communication between the printer and
duplexer had been established but has been lost. Check the cable as
above; if the error persists replace the duplex system board.
23 Paper Jams: Examine the paper path in the duplex unit and in the
fuser exit area for paper or other obstructions. Make sure the duplex
unit is positioned correctly on the printer, and that the gear at the bottom
of the duplex unit meshes with the gear on the top of the paper tray.
Check that the paper is fed with no skew or binds from the duplexer into
the metal channel at the right edge of the tray cover. The tray roller
should move the paper forward when the tray gear is turned, but allow
the paper to be pulled by the D-roll when it picks. Make sure the belt to
the duplex DC motor is in place. Make sure the duplex table cover
(floor) is correctly snapped in place at its front and rear and that the
gear block assembly is correctly snapped into the bottom cover. Run
duplex diagnostics tests #1 and #2 to make sure there is no slippage in
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Service Manual
Voltage to Ground
J3-3 +34VDC
J3-5 +5VDC
J3-7 +5VDC
J5-2 +34VDC
J5-4 +5VDC
J5-6 +5VDC