Apple Laserwriter 8500 Service Manual

K

Service Source

LaserWriter 8500

K

Service Source

Overview

LaserWriter 8500

Overview About This Overview - 1

About This Overview

This overview briefly
describes the servicing
issues of the LaserWriter
8500, especially those that
distinguish it from earlier
Apple laser printers.

360 Degree View

LaserWriter 8500 Basic Configuration

Overview General - 2

General

The LaserWriter 8500 is a 600 dpi, 20 ppm monochrome
laser printer that is capable of printing onto paper up to 13
x 20 inches in size. In its basic configuration, the printer
has a capacity of 650 sheets, the standard cassette holding
500 sheets (as compared to the 250 typical in earlier
printers), the multipurpose tray holding 150.

There are several options available for the printer,
including a duplexer unit (for two-sided printing), a 500-

LaserWriter 8500 with

Duplexer and Sheet Feeder

360 Degree View

sheet feeder, and an envelope cassette.

Overview Duplexer - 3

Duplexer

The duplexer is an inverted L-shaped feeder that mounts

Duplexer

Paper Path

Through Duplexer

onto the upper rear of the printer. Once installed,
(even simplex) diverts into and exits from the duplexer.

This is unlike the LaserWriter 12/640 PS, which employs
a solenoid-actuated diverter controlled through software.
The operative element in the LaserWriter 8500 is the
exchange chute, located in the fuser assembly. The exchange
chute is actuated (i.e. locked in place) during installation of
the duplexer.

After the first pass of a duplex page, the paper partially
exits the duplexer delivery rollers. The rollers then
reverse and the paper feeds back down through the duplexer
and into the printer engine, in preparation for imaging of
the second side. The paper then exits through the duplexer
into the delivery tray.

all

paper

Overview Paper Path - 4

The duplexer derives its power from the printer engine but
has its own motor to generate mechanical drive.

Offset Function

The duplexer has a job separation feature that allows print
jobs to be stacked offset (i.e. staggered left-to-right) in the
delivery tray. Job separation is set in the Apple Printer
Utility.

Note

: Due to cost considerations, the offset function has been
incorporated into the duplexer instead of the printer engine.
Offsetting and duplex printing are otherwise unrelated to one
another.

The offset motor in the duplexer generates the mechanical
drive for offsetting paper.

Overview Sheet Feeder - 5

Sheet Feeder

As with the LaserWriter 16/600 PS and LaserWriter 12/
640 PS designs, the sheet feeder fits squarely beneath the
printer to form a dual front-loading cassette arrangement.
Unlike those models, however, you can stack two feeders

Sheet Feeder

beneath the printer, for a total auxiliary capacity of 1000
sheets. Also unlike those models, the sheet feeder and the
engine use identical cassettes in the LaserWriter 8500.

The sheet feeder derives its power and mechanical drive
from the printer engine.

Overview Form Factor - 6

Form Factor

C

To achieve a reasonably compact form factor, the tail end of
the cassette has been designed to extend out from the engine
footprint (A). Consequently, the pickup rollers feed from

D

A

B

Printer Cross-Section

Note: Diagram shows printer
with long cassette and over­size (11 x 17 inch or A3)
paper installed.

the insertion end of the cassette (B), similar to the Laser­Writer II. This arrangement influences the architecture of
the printer in the following ways.

1 Because pickup occurs deep within the printer, all

mechanical drive elements are arranged vertically along
the rear (C), resulting in a simple C-shaped paper path.
This vertical arrangement yields a compact, low­maintenance gear train, consisting at its essence of one
gear assembly driven by one central motor.

2 You can stack letter-sized paper on the multipurpose

tray and shut the cover (D), thus hiding that paper from
view inside a multipurpose “compartment.”

Overview Form Factor - 7

3 The design of the cassette bottom plate (A) is new.

A

C

Below the plate, three springs provide upward pressure
that forces the paper against the pickup rollers. (Only
two of the springs are activated when the width guides

B

C

(B) are set for narrower paper). In most printers, the
bottom plate receives constant uniform pressure from
the springs. As you insert the cassette, the paper snugly
and passively presses against the pickup rollers.

With this printer, however, the bottom plate must stay
down during insertion to avoid snagging. The springs are
released, and the bottom plate elevated against the pickup
rollers, only when the cassette is fully inserted.

This spring release is actuated by a latch on each side of
the cassette near the leading edge (C). See “Cassette” in
the Basics chapter for more information.

Overview Paper Orientation - 8

Long-Edge Feed

(LEF)

Short-Edge Feed

(SEF)

Feed

Feed

Paper Orientation

The paper path is wide enough to print letter or A4 sized
paper in long-edge feed (LEF) mode. LEF mode is recom­mended as it achieves the fastest 20 ppm throughput and
optimizes duplex printing.

Note

: The cassette automatically senses paper orientation.
The multipurpose tray does not. Printing in short-edge feed
(SEF) mode from the multipurpose tray may produce
undesirable results.

Paper orientation and how best to load paper can be
confusing, especially when talking with customers over the
phone. It is further complicated when printing duplex jobs.
Keep in mind the following tips:

• Use the LEF and SEF terms when talking about how paper

is loaded. These are the terms found in the user manual.

Overview Paper Orientation - 9

• The terms “portrait”
and “landscape” are best
used only when talking
about how a printed page
is to be formatted.
Remember that LEF
mode, for example, can
result in either a
landscape or a portrait
formatted page.

• Load letterhead face-up.

• As you stand facing the
printer: the top of the
page is on the left for LEF
portrait, and on the near
side for LEF landscape.

LEF Paper Orientation

Overview Service Test Page - 10

Service Test Page

A service test page, sometimes called an engine test page, is a
page whose description resides in firmware on the DC
controller board. Successful printing of a service test page
confirms the operation of the print engine. Of equal impor­tance, if a print quality problem appearing on a normal page

Service Test Page

also appears on the service test page, the I/O controller
board is proven good and should not be swapped.

Test Page Button

There are two ways to print a service test page on the Laser­Writer 8500.

1 If the I/O board is installed, use a paper clip to press the

test page button. This button is accessible through a
small unmarked hole at the top of the I/O bracket.

Note

: Use this button liberally, both in person and when

troubleshooting with customers on the phone. It is your

Overview Service Test Page - 11

Test Page Jumper

first line of defense in isolating faults between the I/O
board and printer engine.

2 If the I/O board and shield have been removed from the

printer, you can print a service test page by jumpering
the two pins of connector P23 on the DC controller
board.

Overview RAM Memory - 12

RAM Memory

The LaserWriter comes with 16 megabytes (MB) of RAM soldered onto the I/O
controller board. There is one SIMM slot available for installing additional RAM. The
following table lists the memory requirements and supported paper sizes for duplex
printing and PhotoGrade.

Memory Duplex Printing PhotoGrade Use both features at once?

16 MB Letter, A4, B4, legal Letter, A4, B5 No

20 MB Letter, A3, A4, B4, Up to ledger and A3 Yes; up to letter and A4

legal, ledger

24 MB Letter, A3, A4, B4, Up to Japan Standard Yes; up to legal

legal, ledger and Japan Larger

32 MB Letter, A3, A4, B4, All supported paper Yes; up to B4

legal, ledger sizes

48 MB Letter, A3, A4, B4, All supported paper Yes; all supported paper

legal, ledger sizes sizes

Overview SIMM Sizes and Speeds - 13

SIMM Sizes and Speeds

Size Configuration Speed Connector type
4 MB SIMM 1 M X 32 bit (one 4 MB bank) 70 ns or less 72-pin
8 MB SIMM 2 M X 32 bit (two 4 MB banks) 70 ns or less 72-pin
16 MB SIMM* 4 M X 32 bit (one 16 MB bank) 70 ns or less 72-pin
32 MB SIMM* 8 M X 32 bit (two 16 MB banks) 70 ns or less 72-pin

* Must have a 2 KB row (11 bit x 11 bit) refresh rate. 16 MB SIMMs with a 4 KB row (12 bit x

10 bit) refresh rate are not compatible with the printer.

Overview Miscellaneous - 14

Miscellaneous

Full-Stack Sensor

When the delivery tray is full of paper, the printer stops
accepting print jobs and the controller reports an error
message to the host computer. Sensing of delivery tray
capacity is done through the full-stack sensor located just
above the delivery rollers.

With a duplexer installed, the duplexer full-stack sensor

Actuator for

Full-Stack Sensor

assumes this function. The parts used in the duplexer
actuator and the printer actuator are

not

interchangeable.

Other Sensors and Interlocks

All other sensors and interlocks are similar to previous
printers and will be familiar to the experienced technician.
See “Sensing System Locator” in the Basics chapter for a

Overview Miscellaneous - 15

comprehensive diagram.

There is also a mechanical interlock that disengages the
fuser assembly drive train when the top cover is open (to
facilitate removal of paper jams). See “Top Housing and
Xerographics” in the Basics chapter.

Point-of-Sale (POS) Button

The Ready LED is also a button that actuates a microswitch on
the status panel board. If you hold this LED during printer
startup, the printer will enter the special POS state (or exit
from POS if POS is currently enabled). You can also make
these settings through the Printer Utility.

During POS state, the ready LED flashes two shades of green

Demonstration Page

instead of the normal steady green. When you press the
ready LED thereafter, a special demonstration page will
print. While in POS state, the energy saving feature is

Overview Miscellaneous - 16

disabled, but in all other ways, the printer is network­aware and will perform just as it does in ready state.

Voltage-Specific Parts

Four parts in the printer are available in both 110V and
220V versions:

• Power supply

• Fuser assembly

• Transport chute assembly

• DC controller board

Note

: The DC controller board, though universal in

previous printers, is not in the LaserWriter 8500.
The second version of this board satisfies European

Economic Community requirements and has made possible
some localization of controller board firmware (default
paper size for the multipurpose tray, for example).

Overview Miscellaneous - 17

Density Adjustment

Density Adjustment Dial

On the left side of the multipurpose tray compartment, there
is a density adjustment dial. This dial changes the DC
component of the development bias voltage supplied by the
high-voltage power supply. The dial adjusts the threshold
voltage, in effect changing the background density across the
entire imageable page.

A second method of density adjustment is through the Apple
Printer Utility, which adjusts the laser power output. In
effect, this adjusts the density of the printed pixels.

K

Service Source

Basics

LaserWriter 8500

Basics Function of Main Components - 1

Function of Main Components

This topic describes the function of the following components of the LaserWriter 8500.

•Cassette

•Cassette Feed Components

•Manual Feed Components

•Paper Transportation

•Fusing and Paper Exit

•Frame and Drive

•Top Cover and Xerographics

•Electrical

Cassette

Paper Width Guides

The paper width guides are adjusted left-to-right to accommodate different paper widths.
They contact the left and right sides of the paper stack and hold the paper stack in place in
the crosswise direction.

The left and right snubbers (paper separating claws) at the leading edge of paper allow
only one sheet of paper to be fed from the cassette into the printer. The snubbers move
together with the paper width guides.

Pressure Plate Springs

Two pressure springs act against the bottom plate when paper width is less than 8.5
inches (216 mm). When the paper width is greater, additional forced is deemed necessary
and a third pressure spring is released against the bottom plate. The mechanism that
releases or contains the third spring is controlled by the paper width guides.

Bottom Plate Assembly

Left Width Guide

Size Cams

Pressure Plate Springs

Paper End Guide

Right Width Guide

Basics Function of Main Components - 2

Paper End Guide

The paper end guide can be adjusted front-to-rear to accommodate different paper
lengths. It is in contact with the trailing edge of the paper stack.

When the paper end guide is adjusted, the size cams on the left side of the cassette rotate
into a unique pattern of projections and gaps. When you insert the cassette, the position of
the cams align with actuators that are housed in the printer’s left cassette guide assembly.
The actuators correspond to four microswitches on the cassette feed board.

Cassette

Cassette Feed Board

Size
Cam

Size Actuator
Size Switch

Size
Cam

Size Actuator
Size Switch

Cassette Feed Board

Cassette Latches

On each side near the leading edge of the cassette are two cassette latches. When the
cassette is outside the printer, these latches hold the bottom plate down against the force
of the pressure plate springs. As the cassette is inserted, the latches release and the
bottom plate elevates.

Bottom Plate Assembly

Cassette

Right Cassette

Latch

Bottom Plate Assembly

Cassette Guide

(in Printer)

Basics Function of Main Components - 3

Cassette Feed Components

Turn Clutch

Cassette Feed Solenoid

and Feed Gear

Cassette Feeder Board

The feeder board has the paper size microswitches (see previous topic) and serves as a
relay board for the signals between the cassette feed and the DC controller board.

Cassette Paper-Present Sensor and Actuator

This sensor detects the presence of paper in the cassette.

Cassette Feeder Board

Cassette Paper-Present
Sensor and Actuator

Cassette Feed Solenoid and Feed Gear

When the feed solenoid is actuated, the feed gear is releases and turns to engage with the
feed idler gear. The feed gear then begins to rotate, causing the pickup rollers to rotate.
After one revolution, the feed gear disengages from the feed idler gear and is latched by the
pawl of the feed solenoid.

Turn Clutch

The turn clutch is an electromagnetic clutch that switches on and off the drive power to
the lower and upper feed rollers.

Lower and Upper Feed Rollers

These rollers have an integral metal shaft/rubber roller design. Drive to the rollers is
controlled by the turn clutch so that the rollers start feeding from the pickup area and
stop feeding at the registration sensor.

When the engine receives a /PRFD signal from the controller, the engine stops feeding at
the registration sensor and resumes when it receives a subsequent /START signal. If the /
START signal is received before the paper reaches the registration position, the printer
will feed the paper continuously without stopping the rotation of the feed rollers.

Pickup Rollers

Rotate and feeds one sheet of paper each time the cassette feed solenoid is actuated.

Basics Function of Main Components - 4

Manual Feed Components

Manual Feed

Sensor Assembly

Toner Sensor

Manual Feed Guide Tray

Manual Feed
Paper-Present Sensor

Manual Feed Guide Tray

The manual feed guide tray is the pressure plate and width guide for manual feed paper.
During standby the tray is held down by the pickup roller assembly cams. When the paper
is about to feed, the cams move off the tray due to the rotation of the pickup roller
assembly. The manual feed guide tray is therefore pressed up by the two pressure springs
and the paper is pressed against the pickup roller.

Manual Feed Paper-Present Sensor

Part of the manual feed sensor assembly, this sensor detects the presence of paper in the
manual feed compartment.

Toner Sensor

Also part of the manual feed sensor assembly, this sensor detects low toner by responding
to the magnetism of the toner in the cartridge.

Basics Function of Main Components - 5

Paper Transportation

Transfer Roller Assembly

Transport Chute Assembly

Transfer Roller Assembly

The transfer roller is in contact with the drum in the toner cartridge. The roller is driven
by the drum gear so that the roller surface moves at the same speed as the drum surface.

The transfer roller applies a positive charge to the back side of the paper when the paper
travels between the roller and the drum. The negatively charged toner image transfers
from the drum surface to the front side of the paper because it is attracted by the positive
charge on the back side of the paper.

Transport Chute Assembly

Transport Chute Assembly

Photosensitive Drum

Detack Saw

Transfer Roller

Toner

Cartridge

Registration Actuator

Registration Sensor

Rear Chute Assembly

Rubber Registration Roller

Metal Registration Roller

Pickup Roller

Separation Pad

Included in the transport chute assembly are the following components.

Pickup roller assembly

: Consists of two pickup rollers, three core rollers, pickup cams,
and the shaft. It rotates one turn each time the manual feed pickup solenoid is actuated, and
feeds one sheet of paper from the manual feed compartment.

Pickup solenoid and pickup gear

: When the pickup solenoid is actuated, the pickup gear is
released and turned by the pulling force of the pickup spring to engage with the opposite
gear in the main gear assembly. The pickup gear then begins to rotate, causing the pickup
roller assembly to rotate. After one revolution, the pickup gear disengages from the
opposite gear because of its sector-shaped cutout and is latched by the pawl of the feed

Basics Function of Main Components - 6

solenoid.

Separation pad assembly

: Prevents extra sheets of paper from being fed by the friction

between the paper and the rubber of the separation pad.

Rear chute assembly

: Guides the paper fed from the cassette between the metal and rubber

registration rollers.

Metal registration roller and rubber registration roller

: The rotation of these rollers is
controlled by means of the registration clutch assembly so as to register the paper with
the image on the drum.

Registration sensor

: Detects the arrival and departure of the paper at the registration

position.

T ransfer r oller bearing

: Applies the transfer voltage from the high-voltage power supply to

the transfer roller assembly.

Detack saw

: Imparts a negative charge to the back side of the paper, partially neutralizing

the positive charges, so that the paper can peel off the drum.

Duplexer

The duplexer derives its mechanical drive from the duplex motor. The offset motor
generates the lateral drive for job separation (left-to-right staggering of paper in the
delivery tray).

Offset Gear

Gear B

Gear A

Drive Belt

Duplex Motor

Duplexer

Gear B

Gear C

Gear D

Pulley Gear

Pulley Gear

Basics Function of Main Components - 7

Fusing and Paper Exit

Fuser Assembly

Full Stack Sensor and Actuator

Exit Sensor and Actuator

Thermostat

Temperature Sensor
Assembly

Pressure Roller

Thermal Fuse

The fuser assembly houses all components of fusing (the permanent fixing of toner to
paper by means of heat and pressure), as well as components for paper delivery.

Fuser Bulb

(Inside Heat Roller)

Heat Roller

The heat roller is a hollow metal tube that applies heat to the paper passing between it and
the pressure roller. The heat is generated by the fuser bulb inside the heat roller. This
heat melts the toner on the paper.

Pressure Roller

The pressure roller is a solid, sponge rubber-coated metal shaft that presses the paper
against the heat roller. The pressure helps bond the toner to the paper.

Heater Assembly

The heater assembly consists of the fuser bulb and the wiring and connectors attached to
the ends of the bulb.

Temperature Sensor Assembly

The temperature sensor assembly is a thermistor whose resistance varies sharply with a
change in temperature. This sensor is held in contact with the heat roller surface and
monitors the temperature thereof. The signal from this sensor is used to maintain the
temperature of the heat roller surface within the specified range by switching the power
to the heater bulb on and off. The signal is also used for the first-stage overheat
protection.

Thermostat

The thermostat is part of the heater bulb circuit ad functions as the second-stage overheat

Basics Function of Main Components - 8

protection. If the temperature sensor assembly fails to prevent a fuser overheat, the
thermostat opens and power is cut to the heater bulb.

Thermal Fuse

Also a part of the heater bulb circuit, the thermal fuse functions as the third-stage
overheat protection. If both the first and second stages fail to prevent a fuser overheat, the
thermal fuse opens and power is cut to the heater bulb.

Heat Roller Diode

There is a negative charge that builds up on the heater bulb. This charge can disturb the
toner image on the paper during fusing. The heat roller diode grounds this charge.

Full Stack Sensor

Full Stack Actuator

Exit Sensor

Exit

Chute

Roller

Exit Actuator

Heat Roller Finger

Fuser Assembly

Heat Roller

Pressure Roller

To Duplexer

Exchange
Chute

Heat Roller Fingers

These fingers work in conjunction the non-stick coating of the heat roller to peel the
leading edge of the paper from the roller.

Exit Sensor

The exit sensor detects the arrival and departure of the paper on the delivery side of the
heat roller.

Full Stack Sensor

The full stack sensor detects when the delivery tray is full of paper.

Exchange Chute

The installation of an optional duplexer locks the exchange chute into a position so that all
paper is directed up into the duplexer.

Basics Function of Main Components - 9

Frame and Drive

Main Motor

Registration Clutch

Assembly

Main Gear Assembly

Paper-Handling Gear Assembly

Main Motor

Generates all the drive power for the printer and optional sheet feeder.

Main Gear Assembly

Distributes drive power from the main motor to the fuser assembly, toner cartridge,
paper handling gear assembly, registration clutch assembly, and pickup gear.

Paper Handling Gear Assembly

Transfers the drive power from the main gear assembly to the feed idler gear and to a
second gear within the main gear assembly.

Registration Clutch Assembly

An electromagnetic clutch that switches the drive power on and off to the two registration
rollers at a specified time after the registration sensor has detected the arrival of the
paper. This clutch actuates momentarily after the paper arrives at the registration
rollers to allow the feed rollers to remove any skew induced during paper feed.

Basics Function of Main Components - 10

Top Housing and Xerographics

Guide Arm and Fuser Guide Lever

Fuser Guide

Fuser Assembly

Lever

Top Cover

Main Gear Assembly

Front

When the top cover opens, the fuser guide lever presses down on the floating idler gear at
the top of the main gear assembly, thus disengaging the fuser assembly from the gear
train. This makes removal of paper jams from the fuser much easier. When the top cover
is closed, the floating idler gear springs upward to mate the fuser gearing to the main gear
train.

Cartridge Sensor Assembly

Cartridge-Present Switch LD Switch

Cartridge Sensor Assembly

Toner

Cartridge

Front

The cartridge sensor assembly houses the two switches below.

Cartridge-present switch

: The signal from this switch stops printer operation when the

toner cartridge is absent or the top cover is open.