Macintosh Classic / Classic II General Maintenance

Maintenance guidance for the Macintosh Classic and Macintosh Classic II (and the Performa 200, which is a Classic II). The two machines share a case, a CRT and a service manual, but the logic boards are unrelated: the Classic is a 68000 machine with a memory expansion card, the Classic II a 68030 machine with SIMM sockets on the board.^[1]

Both contain a CRT. Read CRT Discharge Procedure before the case is opened, and do not fit a grounding wriststrap until after the CRT has been discharged.^[1]

Internal cleaning

Power off and unplug before disassembly.
The rear case screws need a long T15 Torx driver; two are deep inside the handle recess.
Separate the case carefully and disconnect the internal cables before lifting the rear shell away.
Compressed air and a soft brush for dust; isopropyl alcohol (>90 %) and an ESD-safe brush for grime and flux.
Dry completely before reassembly.

PRAM battery

Both models use a 3.6 V half-AA lithium cell in a holder. Apple's procedure is to pull the old cell out of the holder and insert the new one the same way round, positive to the "+" marking.^[1]

Apple's replace-below threshold for the Classic and Classic II is 3.0 volts, measured across the cell.^[1] That is this family's figure: the Macintosh SE and Macintosh SE/30 use 2.8 V. Thresholds are not interchangeable between Macintosh models.

Because the cell is lithium, its leakage is neutralised with a bicarbonate of soda solution and not with vinegar — vinegar belongs to the alkaline 4.5 V cell used in the Macintosh Plus and the Macintosh 128K/512K. Work with ventilation; these cells can vent sulphur dioxide.

Symptoms of battery damage:

clock and settings not retained
no boot chime, or no video with drive activity
restart loops
corroded or broken traces near the battery holder

Remove the cell if the machine is going into storage. See Battery Explosion, Capacitor or Corrosion Damage.

Capacitors

Both logic boards carry surface-mount aluminium electrolytics, and both analogue boards carry through-hole electrolytics. Leakage causes no chime, distorted or absent audio, video artefacts, failure to boot and Sad Mac errors. Values and positions are on the Macintosh Classic Capacitor Replacement Guide and the Macintosh Classic II Capacitor Replacement Guide; Capacitor Failure Symptoms covers the general pattern.

The Classic II analogue board exists in 110 V and 220–240 V variants and their reservoir capacitors differ. Work from the table for the board actually in front of you — fitting a part rated for the 110 V board to a 240 V board puts a capacitor on a bus that rectifies to roughly 340 V.

Analogue board and CRT

Solder joints crack with thermal cycling. The usual sites are the flyback transformer leads, the yoke connector and the horizontal output transistor heatsink. Symptoms are flickering, intermittent or missing video. Reflow with added solder.

Note that The Dead Mac Scrolls, the standard component-level reference for the earlier compact Macs, does not cover the Classic or Classic II at all — they were still in warranty when it was written.^[2] Board-reference data quoted for these two machines from that book is being transplanted from the SE.

Fan, speaker and connectors

Fan — replace a noisy or seized unit with an equivalent 12 V fan; check the current draw is comparable.
Speaker — cracked solder joints at the speaker terminals cause audio that cuts in and out.
Connectors — logic board edge connectors oxidise; clean and reseat. SCSI, floppy and power cables work loose.

Memory faults that are not board faults

Apple's own Sad Mac chart for these machines starts with the memory configuration, not the board:^[1]

On the Classic, check that the jumper on the memory expansion board is set correctly for "SIMMs" or "No SIMMs".
On a 4 MB Classic, confirm the SIMMs are eight-chip modules. Apple states that 1 MB SIMMs with fewer than eight chips will not work in the Macintosh Classic.
On the Classic II, suspect the pair of SIMMs in the two logic board slots before the board.

See Macintosh Classic Memory Upgrade Guide, Macintosh Classic II Memory Upgrade Guide, Sad Mac Error Codes and the Sad Mac Decoder.

Power rails: what Apple publishes

Apple publishes no rail voltages, no tolerances and no power-supply adjustment procedure for these machines. The Macintosh Classic/Classic II/Performa 200 Service Source gives only the mains side in its Electrical specification — line voltage 100–120 V AC, 47–63 Hz single phase, 100 W maximum — and its Adjustments chapter covers video and yoke only: light meter setup, cutoff, brightness and contrast, centring, size and focus.^[1]

What you can check is that the rails are inside the range the logic is specified for. 5 V logic is specified for a 5 V supply at ±5 per cent, giving 4.75 V to 5.25 V; treat anything outside that as a fault, and anything that sags under load or carries visible ripple as a fault regardless of the DC reading. Compare against a known-good example of the same model where you can.

Measure at:

the floppy power connector
the Molex power connector, if a hard disk is fitted

Logic board notes

Classic

68000 at 7.8336 MHz, 512 KB ROM, 1 MB soldered RAM, expansion only via the optional memory expansion card.^[1]
One ADB port, not two.^[1]

Classic II

68030 at 16 MHz on a 16-bit external data bus, 512 KB ROM, 2 MB soldered RAM plus two 30-pin SIMM sockets.^[1]
No expansion slot. A microphone is fitted, which the Classic does not have.^[1]
A Classic could be converted to a Classic II with Apple's upgrade kit — a Classic II logic board, a Classic II rear cover, a microphone and an accessory kit — and Apple's instruction was to transfer the original serial number onto the new housing.^[1]

Tools

Long T15 Torx driver
Anti-static wriststrap
Contact cleaner
Isopropyl alcohol (>90 %)
Compressed air or ESD brush
Multimeter

See Recommended Tools.

Related pages

References

↑ ^1.00 ^1.01 ^1.02 ^1.03 ^1.04 ^1.05 ^1.06 ^1.07 ^1.08 ^1.09 ^1.10 Apple Computer, Macintosh Classic/Classic II/Performa 200 Service Source — Specifications, Troubleshooting, Upgrades, Adjustments and Additional Procedures chapters. Hosted on this wiki: File:Classic ii.performa 200.pdf.
↑ Larry Pina, The Dead Mac Scrolls, Peachpit Press, 1992, introduction: "The Mac Classic and Classic II, the LC, IIsi, PowerBooks and Quadras aren't covered at all in this edition." Hosted on this wiki: File:The Dead Mac Scrolls 1992.pdf.

[sscl-1] 1.00 ^1.01 ^1.02 ^1.03 ^1.04 ^1.05 ^1.06 ^1.07 ^1.08 ^1.09 ^1.10 Apple Computer, Macintosh Classic/Classic II/Performa 200 Service Source — Specifications, Troubleshooting, Upgrades, Adjustments and Additional Procedures chapters. Hosted on this wiki: File:Classic ii.performa 200.pdf.

[dms-2] Larry Pina, The Dead Mac Scrolls, Peachpit Press, 1992, introduction: "The Mac Classic and Classic II, the LC, IIsi, PowerBooks and Quadras aren't covered at all in this edition." Hosted on this wiki: File:The Dead Mac Scrolls 1992.pdf.

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