All of these use the same Canon print-engine.
The toner-cartridge drum is not rotating due to a failed "drum-drive assembly." You can mark the periphery of the light-sensitive drum to confirm that it is not rotating.
Remove the top and right covers of the printer. The drum-drive assembly is a white plastic gear/clutch attached to the gear that drives the toner cartridge. Inspect for cracks, replace if necessary. OEM part # RG1-1777- 100, Apple Part # 890-0609. You must partially dismount the entire gear assembly to replace the drum-drive assembly, however, sometimes the new clutch can be slipped onto the old shaft (which does not wear out): Not all shafts are identical.
The upper output-rollers deteriorate (perhaps due to ozone) and become mushy: Replace the roller (Apple "face-down delivery assy." part # 971- 0043 does not fit HP machines, but you can remove the roller and replace that only.)
Inspect the pickup-rollers. If the gray rubber is smooth and shiny on the tips of the cams, replace the rollers. Replace obviously-worn rollers as part of preventive maintenance during other repairs.
When paper feeding begins, a mechanism lifts the paper stack so that the pickup rollers can grab the top sheet. Inspect the lifting mechanism: Sometimes parts at the sides become bent, preventing it from working.
The fuser lamp often burns out because the seals fail and let air into the lamp (resulting in opaque purple/yellow deposits inside the quartz tube). Replacement is easy, requiring minimal disassembly of the fuser. Rarely, the lamp-control circuit in the power supply fails.
The laser-scanner motor commonly fails. Replacement is simple but getting at the scanner requires removing several layers of sheet-metal and circuit boards, the black plastic cover of the scanner housing, and the plastic lens: That may take an hour on your first attempt, 15 minutes with experience. Typically, the IC which drives the scanner motor overheats and visibly discolors the circuit board. HP-IIP, -IIIP and APLW all use the same scanner.
Normally, you can hear the scanner motor running; it whines like a tiny jet-engine starting, a few seconds before the machine begins to feed paper.
Inspect photoelectric sensors, clean with compressed air. If problem persists, re-seat the appropriate connectors on the dc controller board, or replace the entire sensor harness. Failure of the circuit board that holds the contrast control can also cause this indication.
Replace the separation pad (~1x5cm bar with cork-like surface). No tools required.
The high-voltage terminal on the toner cartridge is making bad contact. Placing washers under the two mounting-points of the (white plastic) high- voltage insulator on the cartridge will often extend the terminal enough for good contact.
The detachable paper-feeder contains two solenoids. Under the armature of each is a rectangular black foam pad. If the pads become sticky (as in the HP-II), the paper-feed timing is disturbed. Remove the solenoids, replace the pads. I use double-sided foam tape, then use naphtha to thoroughly remove any glue from the upper surface.
I never encountered this problem until November 1995, then saw several cases in rapid succession: The entire lot of HPIIP-type printers may be reaching an age where this failure is common, so I now inspect the solenoids for stickiness as part of the preventive maintenance of any printer I repair.
Also inspect for broken solder connections on the pins which connect the paper to the printer.
(From: Edward Klotz (email@example.com).)
The worn D-roller assembly can be replaced in about 15 minutes. May as well replace the separation pad also (5 more minutes, fixed at least 6 with new D-roller assemblys from LASER impact out of Texas - about $28 last time I purchased). Also ozone filters are available, very inexpensive (may save a repair down the road).