Apple LaserWriter 12/640 PS Troubleshooting Guide

A LaserWriter 12/640 PS. The three status lights are on the left of the top cover (Mikerajchel, Wikimedia Commons, public domain).

Fault-finding for the Apple LaserWriter 12/640 PS, from Apple's Service Source for the printer and its user's manual. The printer reports faults on three status lights: Ready at the top, Paper Out and Paper Jam. The I/O controller board drives them from the engine's sensors, and the same lights carry the power-on self test (POST) and the technician's extended self test (EPOST). Maintenance is on Apple LaserWriter 12/640 PS General Maintenance.

The fixing rollers run at about 400 °F (204 °C). Apple's user's manual says to let them cool before maintenance or troubleshooting; it gives no time.

Start-up and POST

At switch-on all three lights come on briefly, go out and come on again: that marks the start of POST, which takes about 40 seconds. POST checks three stages in order: the I/O controller's ROM and SIMMs, the rest of the I/O controller, and the DC controller board. It puts the lights out from the top down as each stage passes. If a stage fails, the bottom two lights flash for ever. Note how many lights had gone out first: if only the top light had gone out, the failure was in stage two and the I/O board is at fault.

Status lights after POST (Service Source and user's manual)

Lights	Meaning
Ready on	Ready
Ready flashing	Warming up or processing a job. If it flashes for ever, switch off, disconnect the network and restart: if it stops, look at the network or the host; if it still flashes with the printer on its own, suspect the fan
Paper Out and Paper Jam flashing	POST error. A fuser fault typically shows as: Ready on, Ready flashing, fan on, paper picked for the startup page, then a jam
All off	Top cover open
Paper Out on	No paper or no cassette. Apple notes a faulty scanner motor or main motor can also give this
Paper Out flashing	Waiting for a manual-feed sheet
Paper Jam on	Paper jammed, or toner cartridge missing. With some jams left in the delivery area, the printer can look ready and even pick a sheet before reporting the jam
Paper Jam flashing	Laser/scanner error (Service Source); the user's manual gives a missing toner cartridge

The Ready light can stay on for up to 15 seconds before PostScript reports a fault; wait that long before switching off. The user's manual adds that all three lights on together, or Paper Out and Paper Jam flashing alternately, mean service is needed, and that after a memory upgrade the first thing to check is that the SIMMs are seated in a supported layout.

EPOST

EPOST runs the same three stages with more thorough tests and different codes.

1. Switch off and fit Apple's loopback test plug, part 922-1489, to the LocalTalk port on the I/O controller. Apple's current plug is bright green; the older black plug does not work on this printer, though it does no harm.
2. Switch on. If nothing is wrong, an EPOST test page prints (two duplex pages with a duplexer fitted) and the printer carries on to PostScript.
3. On a fault the lights loop: all on for about a second, all off for about a second, the error code for about a second, all off for about two seconds.

A steady code means an I/O controller fault; a flashing code means an engine fault.

EPOST error codes

Lights shown	Steady	Flashing
Paper Jam	I/O controller board	DC controller board
Paper Out	–	Fuser assembly
Paper Jam and Paper Out	ROM (I/O controller)	Laser/scanner
Ready	General SIMM error	Fan
Ready and Paper Jam	SIMM in slot A/B	Miscellaneous engine error: a paper jam, cover open, no cassette, no paper or duplexer open
Ready and Paper Out	SIMM in slot C/D	Duplexer
All three	–	Toner cartridge missing

After a miscellaneous engine error, look for a jam first: the test often picks up a sheet before the error, and at the next start-up the leftover jam is the first thing reported.

Engine test without the I/O board

The service test page proves the engine. If a print fault also appears on it, the engine is at fault; if the test page is clean, suspect the I/O controller board.

• With the I/O board fitted: jumper the two pins of J101 on the I/O controller board. Starting the printer with these pins already jumpered should bypass POST and force a test print.
• With the I/O board out: on the DC controller interface, behind where the I/O board was, find the pin marked TP using the grid etched on the metal plate below, and jumper it to one of the pins marked G (ground). Take care: some neighbouring pins carry DC voltage.

Known faults

Apple's REA programme

Apple ran a Repair Extension Authorization programme for the 12/640 PS with four preventive repairs. A printer that has had them has a small white dot on the black chassis just left of the cassette opening; a boxed printer has a blue dot on the UPC label.

1. Capacitor C102. An intermittent fault could make the printer report its ready state wrongly. Apple's fix is to remove C102 from the DC controller board, preferably by rocking it until it snaps off and then cutting the leads flush so they cannot short, or by desoldering. If C102 cannot be removed, Apple supplied a DC controller board without it, part 661-1441. Work on an earthed mat with a wrist strap.
2. Exit actuator. Clearing fuser jams can damage the lower exit actuator, near the left end of the fuser pressure roller, through tiny burrs on its tip. Pull it out with its spring, rub the tip with a small piece of paper 10-15 times to burnish it, refit it so that it moves freely with a slight spring return, and wipe the pressure roller with a soft dry cloth. If the actuator is wrongly fitted or the spring is weak, the printer reports a paper jam at power-on. Tape the two upper exit actuators closed while the fuser is out: they are very easily damaged during fuser installation.
3. Cassette pinch roller. The roller must be aligned and sit about 1 mm from the feed roller. Apple's test: hold the cassette top up and slide a business card into the slit between the pinch roller and the moulded paper guide; it should only just stay put. If it falls through, remove the cassette cover (two screws), take off the roller bracket (one screw), flatten its mounting surface if it is bent, and refit it on its two registration pins.
4. Multipurpose tray pressure plate. A good plate pivots about 1.25 cm (half an inch) up and down; a snagged one does not move. Apple's procedure resets the plate and its spring after removing the manual feed pickup roller, its holder and the clutch gear.

Multipurpose tray will not feed

A click from the manual feed solenoid with no roller rotation, or a pressure plate that does not rise, often follows earlier service. Do not separate the two gears of the manual feed clutch gear: a small spring inside can fall off its black arm, and the pickup roller then does not turn and the printer reports a time-out jam. Apple also notes that technicians had dislodged the solenoid flapper that releases the multipurpose pickup roller, leaving the roller turning constantly with jams and noise.

False jam at start-up

The printer reports a jam on the startup page without picking paper, EPOST reports a DC controller error, and a new DC controller board does not help; a service test print runs the motor for about a second and stops. Watch the pickup solenoid through the small hole in the shield over the pickup drive while starting a test print: the pickup motor should spin and the solenoid trigger about a second later. If it does not, the fault is the solenoid, the cassette size sensor board or the cable between them. A faulty cassette size sensor board can make EPOST report a DC controller error.

Other paper faults

• "No paper in the multipurpose tray" while printing from the cassette: the cassette's paper-length guide is set for A4 as shipped. Move it to the letter position, or PostScript's AutoSelect passes the cassette over when looking for letter paper.
• Accordion jams entering the duplexer: the paper guide supplied with the duplexer must be fitted and both locking connectors snapped home. If jams continue, Apple's fix is the vertical duplexer assembly, 922-2001.
• Jams after cassette edges ride over the bracket at the front of the cassette: the printer counts paper over the bracket as a jam. After clearing any jam, open and close the top cover to reset the printer.

Print quality

Apple's print-quality tables P-1 to P-18 all start from the same list of parts to inspect (toner cartridge, mirror assembly, fuser, top cover, power supply, laser/scanner, fuser pressure roller, transfer roller, DC controller, static eliminator) and then work through these checks.

Image problems (Service Source tables P-1 to P-18)

Problem	Apple's checks, in order
Light prints (P-1)	New paper; new toner cartridge; clean the mirror with the peach-coloured slider built into the mirror assembly; drum ground path; obstructions in the beam path; transfer roller; then stop the printer during a print and look at the drum: a poorly developed or poorly transferred image means the high-voltage part of the power supply
Blank prints (P-2)	Toner cartridge; drum ground; beam path; transfer roller; development and transfer on the drum
Black prints (P-3)	Toner cartridge. Cover the laser window with paper: still black means the power supply assembly (charging), then the DC controller. Cover half the window: still black means the laser/scanner, then the DC controller
Vertical band deletions (P-4)	Clean the mirror; paper; toner cartridge (try a second new one with standard paper, since acid paper can cause this); burrs or dirt in the paper path; beam path; transfer roller; fuser rollers
Horizontal band deletions (P-5)	Paper; toner cartridge; development on the drum (power supply, then DC controller); turn the drive gears by hand with the fuser and cartridge out; registration roller; fuser heater roller gears; transfer roller; transfer on the drum; fuser rollers
Vertical streaks (P-6)	Toner cartridge; paper path; beam path; cover the laser window (laser/scanner, then DC controller); transfer roller; fuser rollers
Horizontal streaks (P-7)	Toner cartridge; drum ground; laser window test (power supply, then DC controller); development; transfer roller; fuser rollers
Spot deletions, spots, residual image (P-8 to P-10)	Paper; development; transfer roller; fuser rollers; toner cartridge. Some residual images cannot be avoided; Apple's advice is to change the image or its orientation
Background (P-11)	Development; chute assembly bias transfer roller ground; fuser assembly ground; toner cartridge
Skew (P-12)	Cassette seated and paper loaded properly; paper path; feeder roller; paper transport rollers; toner cartridge
Damaged prints (P-13)	Paper; fuser rollers; skewed feed (P-12); paper path; transport rollers
Unfused image (P-14)	Paper; fuser rollers; pressure between heater and pressure rollers (fuser assembly); paper path
No PhotoGrade (P-15)	At least 12 MB of RAM (20 MB with the duplexer in use)
No duplex printing (P-16)	Driver supplied with the printer or later; at least 12 MB (20 MB with PhotoGrade, 24 MB for duplex PhotoGrade on legal paper)
Duplex back page upside down (P-17)	Binding orientation chosen in the driver
No multipurpose tray printing (P-18)	The manual feed clutch gear spring (see above); recent REA work

A defect that repeats down the page can be matched to a roller. Apple gives the roller diameters for this purpose:

Roller diameters (Principles of Operation p. 13)

Roller	Diameter
Drum	30.0 mm (1.18 in)
Fuser roller	22.6 mm (0.89 in)
Pressure roller	23.0 mm (0.90 in)
Transfer roller	15.9 mm (0.63 in)
Registration feed roller	14.3 mm (0.56 in)
Registration pinch roller	10.0 mm (0.39 in)
Fuser exit roller	13.6 mm (0.53 in)
Fuser pinch roller	8.0 mm (0.31 in)
Delivery roller	8.8 mm (0.34 in)
Delivery pinch roller	10.0-10.8 mm (0.39-0.43 in)
Cassette pickup roller	20.0 mm (0.79 in)
Cassette feed roller	14.0 mm (0.55 in)
Cassette feed pinch roller	20.0 mm (0.79 in)
Preregistration feed roller	14.0 mm (0.55 in)
Preregistration pinch roller	16.0 mm (0.63 in)
Manual feed pickup roller	14.0 mm (0.55 in)

Related pages

• Apple LaserWriter 12/640 PS General Maintenance
• Apple LaserWriter 12/640 PS
• Apple LaserWriter 12/640 PS Documentation