Editing Macintosh 128K/512K Service Source

The '''Macintosh''' volume of Apple's ''Service Source'' is a '''79-page''' service manual for the '''Macintosh 128K and 512K'''. The PDF was distilled on 15 December 1995.

This is one of the most important documents on this wiki, because its '''Adjustments - Voltage''' procedure is the origin of the "+5 V 4.85-5.15 V / +12 V 11.90-12.75 V" figures that have been copied onto Macintosh pages they do not belong to. Here is the procedure as Apple actually prints it.

== The voltage adjustment, verbatim in substance ==
Apple's procedure (Adjustments, pdf pp. 61-66):
# Set the voltmeter to the 20 V scale.
# Connect the '''Macintosh voltage test cable, Apple part number 077-0135''', to the '''external drive port'''. Apple cautions that shorting the test cable plugs to each other can damage the computer, and says to pull the rubber hoods over the plugs.
# Connect the black voltmeter lead between the meter's ground terminal and the computer chassis.
# Connect the '''orange''' test-cable lead to the voltage input terminal. Switch on, and adjust the voltage regulator on the '''power/sweep board''' to between '''11.90 V and 12.75 V'''.
# Switch off, disconnect the orange lead, then connect the '''red''' lead. Switch on, and adjust the regulator to between '''4.85 V and 5.15 V'''.
# Switch off, disconnect, and repeat both tests to verify both voltages are in tolerance. '''If the power/sweep board cannot be adjusted so that both voltages fall within tolerance, replace the board.'''

Apple also notes that the voltages must be verified after replacing either the logic board or the power/sweep board, and that because the adjustment is made from the rear of the computer a '''mirror''' should be used to see the screen rather than reaching around the machine.

Three things follow from this, and they matter because the figures have been mis-applied elsewhere on this wiki:
* The upper +12 V bound is '''12.75 V''', not 12.7 V.
* The adjustment belongs to the '''power/sweep board''' of the 128K, 512K and Plus. Machines without that board - the SE, SE/30, Classic, Classic II, Color Classic and everything later - have no such adjustment, and their ''Service Source'' Adjustments chapters cover yoke and video only.
* It is measured at the '''external drive port''' with a specific Apple test cable, not by probing the board.

== Specifications as printed ==
<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table"
|-
! Item !! Value
|-
| CPU || Motorola 68000 at '''7.83 MHz''', 32-bit internal data bus
|-
| RAM || 128K or 512K
|-
| ROM || 64K
|-
| PRAM || CMOS custom chip with a '''4.5 V user-replaceable battery''' backup, 256 bytes; retains settings with the machine off
|-
| Line voltage || '''105-125 VAC''' (no 220-240 V figure is printed in this manual)
|-
| Frequency || 50-60 Hz
|-
| Maximum power || '''60 W'''
|-
| Size / weight || 13.6 in (34.5 cm) H x 9.6 in (24.4 cm) W x 10.9 in (27.6 cm) D; 16 lb 8 oz (7.5 kg)
|}

The '''4.5 V alkaline''' cell is the one to note: it is not a lithium half-AA, so leakage from it is alkaline and neutralised with vinegar, whereas the lithium cells in later Macs need bicarbonate. See [[Battery Explosion, Capacitor or Corrosion Damage]].

== Contents ==
* '''Basics''' - Overview (pdf pp. 3)
* '''Specifications''' - Processor, Memory, Disk Storage, I/O Interfaces, I/O Devices, Sound and Video, Electrical, Physical (pdf pp. 5-12)
* '''Troubleshooting''' - General, symptom charts for Video, Drives, Peripherals and Miscellaneous (pdf pp. 14-22)
* '''Take Apart''' - Cover, '''Power/Sweep Board''', Logic Board, CRT, Floppy Drive, Chassis (pdf pp. 24-43)
* '''Upgrades''' - Floppy Drive Upgrade Kit, Logic Board Upgrade Kit, '''400K Drive ROM Upgrade''' (pdf pp. 45-59)
* '''Adjustments''' - '''Voltage''', Yoke, Tilt Adjustment, Video (pdf pp. 61-77)
* '''Exploded View''' (pdf pp. 78-79)

== What this manual does not contain ==
No parts list, no schematic and '''no component values'''. The voltage regulator on the power/sweep board is identified by position in a drawing, not by a designator or a part number, and its trimmer is not numbered in this volume. There is no analogue-board capacitor list of any kind. The Electrical specification gives the 105-125 V machine only.

== Pages that cite this document ==
* [[Macintosh 128K/512K General Maintenance]] and [[Macintosh 128K/512K Troubleshooting]] - the voltage adjustment and the 4.5 V PRAM cell.
* [[Macintosh 128K]], [[Macintosh 512K]], [[Macintosh 512Ke]]
* [[Macintosh Plus Service Source]] - the same procedure and the same test cable on the Plus.

''Warning:'' these machines contain a high-vacuum picture tube and a live analogue/power-sweep board. Follow [[CRT Discharge Procedure]] before working inside one; Apple's own Take Apart chapter opens with the same warning.

<pdf> File:Macintosh 128k.512k.pdf </pdf>

Download: [[:File:Macintosh 128k.512k.pdf|Macintosh 128k.512k.pdf]]

[[Category:Service Manuals]]
[[Category:Apple Vintage Computers]]
[[Category:Apple Service Source]]