Apple LaserWriter 4/600 PS Troubleshooting Guide

A LaserWriter 4/600 PS. The three status lights are at the top left (All About Apple museum, CC BY-SA 3.0).

Fault-finding for the Apple LaserWriter 4/600 PS, from Apple's Service Source for the Personal LaserWriter 300, 320 and LaserWriter 4/600 PS and from chapter 4 of Apple's July 1995 Service Guide: LaserWriter Printers, Volume III. The printer shares its Canon P90 engine with the Personal LaserWriter 320, and Apple's troubleshooting tables are the same for both. They are given in full on Apple Personal LaserWriter 320 Troubleshooting Guide; the sections below cover what is particular to the 4/600 PS and what the Service Source adds. Maintenance is on Apple LaserWriter 4/600 PS General Maintenance.

Switch off and unplug the printer before servicing it: it runs at high voltages. Switch it off for at least 5 minutes before working on the fuser. After fitting a replacement fuser assembly, Apple says to wait at least 10 minutes before plugging the printer in, to let the capacitor discharge.

Status lights

The printer has three status lights: Ready/In Use at the top, Paper-Out and Paper-Jam.

Status lights in normal use (Service Source, Basics p. 10)

Condition	Ready/In Use	Paper-Out	Paper-Jam
Warming up or processing	Flashing	Off	Off
Ready	On	Off	Off
Out of paper (cassette feed selected)	Off	On	Off
Paper jam	Off	Off	On

At switch-on all three lights come on. Ready/In Use goes out when the I/O controller board passes its self test, Paper-Out when the RAM card passes and Paper-Jam when the engine passes, so the light left on shows where a start-up fault is. The 1995 service guide describes this power-on self test for both the 320 and the 4/600 PS; the Service Source describes it for the 320 only.

Engine diagnostic

The diagnostic is built into the I/O board. Switch off, fit a serial loopback plug to the serial connector on the I/O board and switch on; the lights can take up to 90 seconds to show a result. The Service Source gives the loopback as 922-1489, the 1995 service guide as 077-8265. If the diagnostic finds a fault, the lights repeat until the printer is switched off: all on for a second, all off for a second, the error pattern for a second, all off for a second.

Engine diagnostic error patterns (Service Source, Troubleshooting p. 6)

Fault	Ready/In Use	Paper-Out	Paper-Jam
Controller assembly	Off	Off	On
RAM card	Off	On	Off
Fuser assembly	On	Off	Off
Fan motor	Off	On	On
Laser assembly	On	Off	On
Other engine fault	On	On	Off

Service test page

The service test page, a series of vertical lines, is generated by the controller assembly alone, so a good one shows the engine works. To print it, load paper, fit a toner cartridge and switch on, then raise the edge of the printer and pull the plastic test print lever underneath. Wait until the I/O startup page has printed, or until it is clear that none will: a test page started before that comes out all black on a working printer.

Several of Apple's print-quality tables use it to split the I/O board from the engine: a fault that appears only on pages from the Macintosh, never on the service test page, means the I/O board. If the printer goes through its normal start-up (the fan runs and the delivery rollers turn) but will not print a service test page, the fault is most likely the controller assembly or the pickup solenoid.

Quick reference

The Service Source opens its troubleshooting chapter with short fault lists for the whole family. Work down each list in order.

Quick-reference faults (Service Source, Troubleshooting pp. 23-30)

Symptom	Apple's steps
No mains power	Check the outlet voltage and the power cord at both ends; replace fuse FU101 on the controller assembly; replace the controller assembly
No DC power	Find what tripped the overcurrent detection circuit on the controller assembly; replace fuse FU201; replace the controller assembly
No pickup from the manual-feed slot	Arm registration assembly, if broken; pickup motor assembly; controller assembly
No pickup from the cassette	Cassette-empty sensor lever, if broken; pickup solenoid on the controller assembly; pickup roller, if damaged; pickup motor assembly; controller assembly
Paper-Jam light with no jam	Arm registration assembly, if broken; paper delivery sensor, if broken; controller assembly
Motor does not turn	Motor contact with the controller assembly at J601; main motor; controller assembly
Fan does not run	Fan contact with the laser/scanner assembly at J804; fan; controller assembly
No power to the fuser	Fuser seated and contacting the controller assembly at J103 and J204; fuser assembly (then wait 10 minutes before plugging in); controller assembly
Printer drops its connection to the Macintosh after three pages	Replace the fan
Room lights flicker when the printer starts a page	Reported on the Personal LaserWriter 300 and 320; a new controller assembly cured every reported case

Interrupting a print

To tell an imaging fault from a fusing fault, start a print, wait about 12 seconds after the paper is picked from the cassette, and stop the printer after the image has transferred to the paper but before the paper leaves the fuser. Take out the toner cartridge, turn it over, pull back the drum shield and look at the drum. If the drum shows the same fault as the page, the cause is before the drum, in the imaging system; if the drum is clean, it is after it, probably the fuser or the controller assembly.

Apple's flowchart and tables

Apple's flowchart for the 320 and 4/600 PS starts with a Macintosh using the LaserWriter 8 driver. Clear any jam, fit a cartridge, fill the cassette and plug the printer in. If the fan does not run, go to Table 1; if the main motor does not turn at start-up, Table 2. Then print a window or the desktop: follow any error message on the Macintosh, replacing a module if the message names one, and go to the print-quality tables for a poor page. Without a Macintosh, remove the cover and I/O board, defeat paper delivery sensor PS301 with folded paper, cover the laser/scanner with paper, hold down the toner cartridge and the cover interlock actuator, and use the same first two tables; then print a service test page, with paper transport faults going to Tables 3 to 6.

In every table, retry the printer after each change, and if a new module does not cure the fault, refit the original before the next step.

Where Apple's tables are

Fault	Service Source table	1995 service guide table
No power to fan	1	81
Main motor failure	2	82
No pickup from the cassette	3	83
No pickup from the manual-feed slot	4	84
Jams in the pickup or transfer area	5	85
Jams in the fuser or delivery area	6	86
All-blank, all-black, light and dark pages	7 to 10	87 to 90
Vertical lines, irregular lines and stairstepping	11 to 14	91 to 94
Horizontal banding and lines	15 and 16	95 and 96
Registration, skew, fusing, toner on the back, blank spots	17 to 21	97 to 101
Personal LaserWriter 320 memory (PhotoGrade, legal edge to edge)	22 and 23	102 and 103

The steps of every table are set out on Apple Personal LaserWriter 320 Troubleshooting Guide#Power and engine and Apple Personal LaserWriter 320 Troubleshooting Guide#Print quality. Among them: if the fan will not run, Apple's first step is to unplug the printer with a cartridge fitted and wait 4 minutes before plugging it in again, "because of the possibility of a capacitor error". With the fuser removed, its resistance across J204-1 and J204-2 should be about 440 kΩ, and J103-1 to J103-2 should show continuity. For the 4/600 PS, use its own controller assembly (661-0201 or 661-0203), I/O board (661-0200) and laser/scanner (661-0202) when a table calls for a module exchange.

Related pages

• Apple LaserWriter 4/600 PS
• Apple LaserWriter 4/600 PS General Maintenance
• Personal LaserWriter 300/320 and LaserWriter 4/600 PS Service Source
• Apple Personal LaserWriter 320 Troubleshooting Guide