Apple Macintosh 512k Service Manual

K

Service Source

Macintosh

K

Service Source

Basics

Macintosh

Basics Overview - 1

Overview

This manual includes repair
procedures for the earliest
Apple Macintosh
computers—the Macintosh
128K and Macintosh 512K.

Figure: Macintosh 128k/512K

K

Service Source

Specifications

Macintosh

Specifications Processor - 1

Processor

CPU

Motorola 68000 microprocessor

7.83 MHz
32-bit internal data bus

Specifications Memory - 2

Memory

RAM
ROM
PRAM

128K or 512K
64K
CMOS custom chip with 4.5 V, user-replaceable battery backup

(includes 256 bytes of memory; remembers system
parameters even with the machine switched off)

Specifications Disk Storage - 3

Disk Storage

Floppy Drive

Internal, single-sided drive; uses 3.5-in., hard-case, 400K

floppy disks

Specifications I/O Interfaces - 4

I/O Interfaces

Floppy Drive

Mouse

Keyboard

Serial

External drive port; DB-19 connector

Mouse port; DE-9 connector

Synchronous serial keyboard bus; RJ-11 connector

Two RS-232/RS-422 serial ports; DE-9 connectors

Specifications I/O Devices - 5

I/O Devices

Keyboard

Mouse

58 keys; software mapped; RJ-11 connector

Mechanical tracking; optical shaft encoding at 3.54 pulses per mm
(90 pulses per in.) of travel; DE-9 connector

Specifications Sound and Video - 6

Sound and Video

Sound Generator

Video Display

Four-voice sound with 8-bit digital/analog conversion, using
22-kHz sampling rate

9-in. (diagonal) screen; 512 x 342 pixel, bit-mapped display

Specifications Electrical - 7

Electrical

Line V oltage

Frequency

Maximum Power

105–125 VAC

50–60 Hz

60 W

Specifications Physical - 8

Physical

Dimensions

Weight

Height: 13.6-in. (34.5 cm)
Width: 9.6-in. (24.4 cm)
Depth: 10.9-in. (27.6 cm)

16 lb. 8 oz. (7.5 kg)

K

Service Source

Troubleshooting

Macintosh

Troubleshooting General/ - 1

General

The Symptom Charts included in this chapter will help you
diagnose specific symptoms related to your product. Because
cures are listed on the charts in the order of most likely solution,
try the first cure first. Verify whether or not the product
continues to exhibit the symptom. If the symptom persists, try
the next cure. (Note: If you have replaced a module, reinstall the
original module before you proceed to the next cure.)

If you are not sure what the problem is, or if the Symptom Charts
do not resolve the problem, refer to the Flowchart for the product
family.

For additional assistance, contact Apple Technical Support.

Troubleshooting Symptom Charts/Video - 2

Symptom Charts

Video

No video, but audio
tone is present and
drive operates

Screen is bright and
audio is present, but
no video information
is present

1 Turn contrast control fully clockwise.
2 Check video cable connections.
3 Replace power supply board.
4 Replace neck cable.
5 Replace logic board. Retain customer’s SIMMs.

1 Replace power supply board.
2 Replace logic board. Retain customer’s SIMMs.

Troubleshooting Symptom Charts/Drives - 3

Drives

Disk ejects; display
shows disk icon with
blinking “X”

Unable to insert disk
all the way

1 Replace bad disk.
2 Replace floppy drive cable.
3 Replace drive.
4 Replace logic board. Retain customer’s SIMMs.

1 Insert opened paper clip into small hole beside drive slot, or

switch off system power and hold mouse ∑∑button down
while switching system power back on to complete eject
cycle. Then insert disk with metal slot forward and write­protect tab on bottom.

2 Replace floppy drive.

Troubleshooting Symptom Charts/Drives

(Continued)

- 4

Drive does not eject
disk

Does not read disks
on internal drive

Drives

Insert opened paper clip into small hole beside drive slot, or switch
off system power and hold mouse button down while switching
system power back on to complete eject cycle.

1 Replace bad disk.
2 Replace floppy drive cable.
3 Replace Mylar RFI shield.
4 Replace floppy drive.
5 Verify ROMs on the logic board (refer to Additional

6 Replace logic board. Retain customer’s SIMMs.

(Continued)

Procedures).

Troubleshooting Symptom Charts/Peripherals - 5

Peripherals

Cursor does not move 1 Connect mouse.

2 Replace mouse.
3 Replace logic board. Retain customer’s SIMMs.

Cursor moves, but
clicking mouse
produces no response

No response to any
key on keyboard

No response from a
particular key

1 Replace mouse.
2 Replace logic board. Retain customer’s SIMMs.

1 Replace keyboard cable.
2 Replace keyboard.
3 Replace logic board. Retain customer’s SIMMs.

1 Replace keyswitch.
2 Replace keyboard.
3 Replace logic board. Retain customer’s SIMMs.

Troubleshooting Symptom Charts/Peripherals

(Continued)

- 6

Known-good
ImageWriter or
ImageWriter II does
not print

Known-good
LaserWriter does not
print

Peripherals

1 Make sure that Chooser and Control Panel are set correctly
2 Check that system software version is compatible. Replace

software with known-good version.
3 Reset PRAM.
4 Replace interface cable.
5 Replace logic board. Retain customer’s SIMMs.

1 Make sure that Chooser and Control Panel are set correctly.
2 Check that system software version is compatible. Replace

software with known-good version.
3 Reset PRAM.

(Continued)

Troubleshooting Symptom Charts/Miscellaneous - 7

Miscellaneous

When turned on, the
Macintosh
continuously beeps
and tries to power up

Clicking or chirping
sound

1 Perform voltage adjustment. Refer to Adjustments chapter.
2 Disconnect internal disk drive. If this eliminate problem,

replace drive.
3 Replace logic board. Retain customer’s SIMMs.
4

Caution:

new power supply board. Replace power supply board, logic

board, and internal drive, then turn on Macintosh.

1 Connect logic board cable.
2 Perform voltage adjustment. Refer to Adjustments chapter.
3 Replace power supply board.
4 Replace logic board. Retain customer’s SIMMs.

Replacing only power supply board may damage

Troubleshooting Symptom Charts/Miscellaneous

(Continued)

- 8

Smoke/odor issues
from the Macintosh

No video, no audio
tone, and no drive
operation

Miscellaneous

Caution:

power supply board. Replace power supply board, logic board, and
internal drive, then turn on Macintosh.

1 Connect power cord.
2 Turn on power.
3 Replace power cord.
4 Check fuse.
5

6 Replace logic board. Retain customer’s SIMMs.

Replacing only power supply board may damage new

Caution:

new power supply board. Replace power supply board, logic

board, and internal drive, then turn on Macintosh.

(Continued)

Replacing only power supply board may damage

Troubleshooting Symptom Charts/Miscellaneous

(Continued)

- 9

When developer’s
switch is installed,
Macintosh sometimes
resets intermittently

Macintosh 512K
enhanced has two RFI
shields

Miscellaneous

Remove switch and file it down about 1/16 inch.

Some machines have two RFI shrouds installed. Two RFI shields
can be replaced by one RFI shield, which can be ordered as a
service part.

(Continued)

K

Service Source

T ak e Apart

Macintosh

Take Apart Cover - 1

Cover

No preliminary steps are
required before you begin
this procedure.

±

Warning:

contains high voltage and a
high-vacuum picture tube.
To prevent serious injury
or equipment damage,
review CRT safety and
discharge instructions in
Bulletins/Safety.

This product

Take Apart Cover - 2

Cover

Battery
Compartment
Cover

1 Remove the battery

compartment cover.

2 Remove the reset/

interrupt switch, if
present.

Reset/Interrupt
Switch

Take Apart Cover - 3

3 Using a Torx

screwdriver, remove
the four case screws.

4 Using the pull-apart

tool, gently pry off the
cover.

±

Warning:

the metal chassis may
be sharp. When moving
the computer with the
cover off, be sure to
handle the chassis
carefully.

The edges of

Take Apart Cover - 4

5 Remove the RFI shield.

RFI Shield

Take Apart Power/Sweep Board - 5

Ground Lug

Anode Cap

Discharge
Tool

Power/Sweep Board

Power/Sweep
Board

Before you begin,

• Remove the cover

• Discharge the CRT

• Remove the anode cap

±

Warning:

contains high voltage and a
high-vacuum picture tube.
To prevent serious personal
injury or equipment
damage, review CRT safety
and discharge instructions
Bulletins/Safety.

This product

Take Apart Power/Sweep Board - 6

±

Yoke Cable

Logic Board
Cable

Neck Cable

Screw and
Lockwasher

Warning:

grounding wriststrap until
after discharging the CRT.

1 Disconnect the following

cable connectors from
the power/sweep board:

• Yoke cable

• Logic board cable

• Neck cable

2 Remove the screw and

lockwasher that hold the
ground wire to the
chassis.

Never use a

Take Apart Power/Sweep Board - 7

3

Note:

You may need to
remove the insulating
paper from the power/
sweep board to access the
mounting screws.

Remove the three
mounting screws and
washers, and lift the
power/sweep board
from the chassis.

Replacement Note:

replacing all parts except
the cover, perform the
voltage and video
adjustment procedures. See
“Voltage” and “Video” in the
Adjustments chapter.

After

Take Apart Power/Sweep Board - 8

Replacement Note:

sending a defective power/
sweep board to Apple, be
sure to include the cable that
connects to the logic board.
Be sure the contrast control
knob and battery have been
removed from the defective
board and reinstalled onto
the exchange board.

When

Take Apart Logic Board - 9

Logic Board

Before you begin,

• Remove the cover

• Discharge the CRT

±

Warning:

contains high voltage and a
high-vacuum picture tube.
To prevent serious personal
injury or equipment
damage, review CRT safety
and discharge instructions
in Bulletins/Safety.

Logic Board

This product

Take Apart Logic Board - 10

±

Warning:

grounding wriststrap until
after discharging the CRT.

1 Disconnect the following

cable connectors from
the logic board:

• Floppy drive cable

• Logic board cable

Logic
Board

Cable

Floppy Drive Cable

Never use a

Take Apart Logic Board - 11

2

Caution:

removing the logic
board, be careful not to
damage the SIMMs —
especially the larger DIP
SIMMs that may be
installed on the board.

Pull back on the top of
the logic board, and
carefully slide out the
logic board.

When

Replacement Note:

replacing all parts except
the cover, perform the
voltage and video
adjustment procedures. See
“Voltage” in Adjustments.

After

Take Apart Logic Board - 12

Replacement Note:

exchanging the 512K logic
board, you must swap ROMs
to the new logic board.

Replacement Note:

the SIMMs from the
defective logic board and
install them on the
replacement logic board.
See Hardware/Memory.

When

Remove

Take Apart CRT - 13

CRT

CRT

Before you begin,

• Remove the cover

• Discharge the CRT

• Remove the Power/
Sweep board

±

Warning:

contains high voltage and a
high-vacuum picture tube.
To prevent serious personal
injury, review CRT safety
and discharge instructions
in Bulletins/Safety.

This product

Take Apart CRT - 14

±

Ground

Wire

Warning:

grounding wriststrap until
after discharging the CRT.

±

Warning:

by its sides only. Do not
grasp the neck on the CRT or
touch the anode.

1 Slide the CRT socket

cable straight off the
neck of the CRT.

2 Remove the four

mounting screws and the
ground wire, and lift the
CRT off the bezel.

Never use a

Handle the CRT

Take Apart CRT - 15

±

Warning:

dispose of the CRT, refer to
“CRT Disposal” in
Bulletins/Safety.

If you must

Replacement Note:

replace the CRT, perform
the video and yoke
adjustment procedures. See
“Video” and “Yoke” in the
Adjustments chapter.

If you

Take Apart Floppy Drive - 16

Floppy Drive

Before you begin,

• Remove the cover

• Discharge the CRT

• Remove the logic board

±

Floppy Drive

Warning:

contains high voltage and a
high-vacuum picture tube.
To prevent serious personal
injury or equipment
damage, review CRT safety
and discharge instructions
in Bulletins/Safety.

This product

Take Apart Floppy Drive - 17

Floppy Drive

±Warning:

Never use a
grounding wriststrap until
after discharging the CRT.

Remove the four mounting
screws, and slide the floppy
drive out of the chassis.

Take Apart Floppy Drive - 18

Replacement Note:

400K drives are shipped in
their original drive shields.
When installing a new
800K drive, remove the
shipping fixture, plastic
dust shield (if any), and
packing disk from the new
drive. Install the new drive
in the customer’s original
drive shield.

Note:

Before you install a
replacement drive, remove
the dust shield, if there is
one.

All

Take Apart Chassis - 19

Chassis

Before you begin,

• Remove the cover

• Discharge the CRT

• Remove the logic board

• Remove the Power/

Sweep board

• Remove the floppy drive

±

Chassis

Warning:

contains high voltage and a
high-vacuum picture tube.
To prevent serious personal
injury or equipment
damage, review CRT safety
and discharge instructions
in Bulletins/Safety.

This product

Take Apart Chassis - 20

±

Warning:

grounding wriststrap until
after discharging the CRT.

Remove the five mounting
screws and lift the chassis
off the bezel.

Never use a

K

Service Source

Upgrades

Macintosh

Upgrades Floppy Drive Upgrade Kit - 1

Floppy Drive Upgrade Kit

Before you begin,

• Remove the cover

• Discharge the CRT

• Remove the logic board

Floppy Drive

±

Warning:

contains high voltage and a
high-vacuum picture tube.
To prevent serious personal
injury or equipment
damage, review CRT safety
and discharge instructions
in Bulletins/Safety.

This product

Upgrades Floppy Drive Upgrade Kit - 2

±

D5

D8

Warning:

grounding wriststrap until
after discharging the CRT.

Note:

This kit replaces the
400K floppy drive on a
512K Macintosh with an
800K floppy drive. The kit
contains the new drive and
two new ROMs for the logic
board. The new ROMs
support both the 400K and
the 800K drives. This
upgrade is not recommended
for the 128K Macintosh.

Never use a

Upgrades Floppy Drive Upgrade Kit - 3

1 Using an IC extractor,

remove the old ROMs
from locations D5 and
D8.

2 Install the two new ROMs

as follows:

• ROM HI at location D5

D5

D8

• ROM LOW at location
D8

Note:

Be sure that the
notched ends of the
ROMs face the front of
the computer.

Upgrades Floppy Drive Upgrade Kit - 4

3 Remove the floppy drive.

Refer to “Floppy
Drive” in the Take Apart
chapter.

Upgrades Floppy Drive Upgrade Kit - 5

4 Reinstall the logic board.

See “Logic Board” in
the Take Apart chapter.

Upgrades Floppy Drive Upgrade Kit - 6

5 Install the new 800K

floppy drive. See
“Floppy Drive” in the
Take Apart chapter.

6 Return the old ROMs and

the 400K drive to Apple
(refer to the
instructions in the kit).

Upgrades Logic Board Upgrade Kit - 7

Logic Board Upgrade Kit

Before you begin,

• Remove the cover

• Discharge the CRT

• Remove the logic board

±

Logic Board

Warning:

contains high voltage and a
high-vacuum picture tube.
To prevent serious personal
injury or equipment
damage, review CRT safety
and discharge instructions
in Bulletins/Safety.

This product

Upgrades Logic Board Upgrade Kit - 8

±

D5

D8

Warning:

grounding wriststrap until
after discharging the CRT.

Note:

This kit cannot be
installed unless the Floppy
Drive Upgrade Kit has been
installed. The Logic Board
Upgrade Kit upgrades the
logic board of a 512K Mac to
a Mac Plus. The kit contains
a new logic board with 1 MB
of RAM, an RFI shield, and a
new rear cover.

Never use a

Upgrades Logic Board Upgrade Kit - 9

1 Using an IC extractor,

remove the ROMs from
locations D5 and D8 on
the 512K logic board.

2 Install the two ROMs in

the new logic board:

• ROM HI at location D5

D5

D8

• ROM LOW at location
D8

Note:

Be sure that the
notched ends of the
ROMs face the front of
the computer.

Upgrades Logic Board Upgrade Kit - 10

3 Install the new logic

board in the computer.
See “Logic Board” in
the Take Apart chapter.

Upgrades Logic Board Upgrade Kit - 11

4 Install the new RFI

shield.

5 Install the new cover.

See “Cover” in the Take
Apart chapter.

6 Return the old logic

board, old RFI shield,
and old cover to Apple.

Upgrades 400K Drive ROM Upgrade - 12

400K Drive ROM Upgrade

Before you begin,

• Remove the cover

• Discharge the CRT

• Remove the logic board

±

Logic Board

Warning:

contains high voltage and a
high-vacuum picture tube.
To prevent serious personal
injury or equipment
damage, review CRT safety
and discharge instructions
in Bulletins/Safety.

This product

Upgrades 400K Drive ROM Upgrade - 13

±

D5 D8

Warning:

grounding wriststrap until
after discharging the CRT.

Note:

Current 400K drives
contain a new stepper motor
that requires the
replacement of the two boot
ROMs on the Macintosh
128K and 512K. The new
ROMs are compatible with
new and old stepper motors.

1 Using an IC extractor,

remove the ROMs at
locations D5 and D8.

Never use a

Upgrades 400K Drive ROM Upgrade - 14

2 Install the two new ROMs

on the logic board:

• ROM HI at location D5

• ROM LOW at location
D8

Note:

Be sure that the

notched ends of the

D5

D8

ROMs face the front of
the computer.

Upgrades 400K Drive ROM Upgrade - 15

3 Reinstall the logic board

in the computer. See
“Logic Board” in the
Take Apart chapter.

K

Service Source

Adjustments

Macintosh

Adjustments Voltage - 1

Voltage

Before you begin, remove
the cover.

±

Warning:

contains high voltage and a
high-vacuum picture tube.
To prevent serious personal
injury or equipment
damage, review CRT safety
and discharge instructions
in Bulletins/Safety.

This product

Adjustments Voltage - 2

Power/Sweep
Board

External
Drive Port

Caution:

Because you must
make voltage adjustments
from the rear of the
computer, use a mirror to
view the computer screen.
Do not reach around the
computer to adjust the
controls.

Note:

You must verify
voltages after you replace
the logic board or the
power/sweep board.

Adjustments Voltage - 3

1 Set the voltmeter to 20 V

scale.

2 Connect the Macintosh

voltage test cable (Apple
part number 077-

0135) to the external
drive port.

External
Drive Port

Caution:

Shorting the test
cable plugs to each other can
damage the Macintosh
computer. Pull the rubber
hoods over the plugs.

3 Connect the black

voltmeter test lead
between the voltmeter

Adjustments Voltage - 4

ground terminal and the
computer chassis.

4 Connect the orange test

cable lead to the voltage
input terminal on the
voltmeter.

5 Switch on the computer.

Voltage

Regulator

Power/Sweep

Board

6 Adjust the voltage

regulator on the power/
sweep board to between

11.90 V and 12.75 V.

7 Switch off the power.

8 Disconnect the orange

test lead and pull the
insulated hood over the
plug.

Adjustments Voltage - 5

9 Connect the red test

cable lead to the voltage
input terminal on the
voltmeter.

10 Switch on the computer.

11 Adjust the voltage

regulator on the power/

Voltage
Regulator

sweep board to between

4.85 V and 5.15 V.

Power/Sweep

Board

Adjustments Voltage - 6

12 Switch off the power.

13 Disconnect the red test

lead

14 and pull the insulated

hood over the plug.

15 Repeat the tests to verify

that both voltages are

Voltage
Regulator

within the specified
tolerances.

Note:

If the power/sweep

board will not adjust so that

Power/Sweep

Board

both voltages fall within
tolerance, replace the board.

Adjustments Yoke - 7

Yoke

Before you begin,

• Remove the cover

• Discharge the CRT

±

Yoke

Warning:

contains high voltage and a
high-vacuum picture tube.
To prevent serious personal
injury or equipment
damage, review CRT safety
and discharge instructions
in Bulletins/Safety.

This product

Adjustments Yoke - 8

Caution:

make yoke adjustments from
the rear of the computer,
use a mirror to view the
computer screen. Do not
reach around the computer
to adjust the controls.

Note:

CRT, you may need to adjust
the yoke.

Because you must

If you replace the

Adjustments Tilt Adjustment - 9

Tilt Adjustment

Note:

If glue holds the yoke
collar in place, use an art
knife to cut through the glue.

1 Loosen the yoke clamp

Yoke Collar

Yoke Clamp
Screw

screw two or three
turns.

2 Switch on the computer.

Adjustments Tilt Adjustment - 10

3 With one hand, grasp

the plastic spokes of the
yoke collar and rotate
the yoke collar until the
top and bottom edges of
the picture are parallel
with the top and bottom

Yoke Collar

of the bezel.

Adjustments Tilt Adjustment - 11

4 Switch off and unplug the

computer.

5 Discharge the CRT.

6

Caution:

Do not
overtighten the yoke
clamp screw.

Yoke Collar

Hold the plastic collar

Yoke Clamp
Screw

in position and slowly
tighten the yoke clamp
screw so that the collar
cannot slip.

Adjustments Tilt Adjustment - 12

7 Replace the cover and

switch on the computer.

8 Make sure the top and

bottom edges of the
picture are parallel with
the top and bottom of the
bezel.

Adjustments Tilt Adjustment - 13

Centering Ring Adjustment

1 Turn off the computer

and remove the cover.

2 Turn on the computer

Note:

If glue holds the yoke
collar in place, use an art
knife to cut through the glue.

3 To center the picture,

hold the front centering
ring steady and move the
rear ring. Then hold the
rear centering ring

Centering Rings

steady and move the
front ring.

Adjustments Video - 14

Power/Sweep
Board

Video

Before you begin, remove
cover.

±

Warning:

contains high voltage and a
high-vacuum picture tube.
To prevent serious personal
injury, review CRT safety
and discharge instructions
in Bulletins/Safety.

Note:

You must perform the
video adjustments whenever
the CRT or the power/sweep
board is replaced.

Switch on the computer.

This product

Adjustments Video - 15

Contrast and Brightness

1 Turn the external

contrast control fully
clockwise.

Brightness
Control

External
Contrast
Control

2 Turn the brightness

control fully
counterclockwise so that
white lines are visible.

3 Turn the brightness

control clockwise until
the white lines just
disappear.

4 Turn the external

contrast control 1/8 of a
turn counterclockwise.

Adjustments Video - 16

Size Adjustment

1 Using an alignment tool,

adjust the width control
until the raster is 7

Width Control

Height Control

inches (177.8 mm)
wide.

2 Using an alignment tool,

adjust the height control
until the raster is 4.7
inches (119.4 mm)
high.

Adjustments Video - 17

Focus Adjustment

1 Turn the focus control

clockwise to its limit.

2 Turn the focus control

counterclockwise 1/8 of
a turn.

Focus Control

K

Service Source

Exploded V ie w

Macintosh

Exploded View 1

Exploded View

Internal Drive
Shield
805-0765 (400K)
805-0217 (800K)

Floppy Drive
661-7615 (400K)
661-0345 (800K)

Internal
Drive
Cable
590-0167 (red)
590-0437 (yellow)

Insulator
Shield
725-0011

Front

Bezel

810-0373

CRT and Yoke

Assembly

076-0103

CRT

Socket

Cable

590-0160

Chassis

805-0766

Rear Housing

630-5139

462-3100

Power/Sweep
Board
661-76214

426-1001

Logic Board
661-06236

RFI Shroud
805-0577

426-1007

435-5002