Macintosh Classic / Classic II General Maintenance

Macintosh Classic with the rear cover removed: CRT, power/sweep board (right), logic board and memory expansion card (bottom). Photo: htomari, CC BY-SA 2.0, via Wikimedia Commons

Maintenance guidance for the Macintosh Classic and the Macintosh Classic II, including the Macintosh Performa 200, which is a Classic II. The two machines share a case, a CRT, a power/sweep board and one Apple service manual. Their logic boards differ: the Classic is a 68000 machine with an optional memory expansion card, the Classic II a 68030 machine with two SIMM sockets on the board.

Safety

Both machines contain a CRT and a mains-connected power/sweep board. Read CRT Discharge Procedure before opening the case. Apple's order is to discharge the CRT before putting on a grounding wriststrap, never the reverse. For the Classic II, Apple's Service Guide says the CRT is discharged to the ground lug to avoid damaging the logic board. The same guide puts the anode at up to 12,000 V DC for its Macintosh CRTs.

Opening the case

1. Switch off and unplug the machine. Lay it face down on a soft cloth.
2. Remove the four Torx T15 case screws. Two are by the ports and two are deep inside the handle recess, so a long driver is needed.
3. Separate the cover from the chassis with a case spreader and lift it away.
4. Discharge the CRT.
5. The chassis edges are sharp; handle it carefully with the cover off.

On reassembly the two black case screws go in the bottom of the cover and the two silver screws in the top.

Cleaning

• Blow dust out of the chassis, the power/sweep board and the CRT neck area with compressed air.
• Clean grime and old flux off the boards with isopropyl alcohol and a soft ESD-safe brush, and let everything dry before power is applied.
• Clean the case separately with mild soap and water. See Retrobrite for yellowing.

PRAM battery

The battery is a lithium cell, Apple part 742-0011, on the logic board. Low End Mac gives it as a 3.6 V half-AA cell for both machines.

Apple's test is to remove the logic board, set the meter to the 10 V DC range, and replace the cell if it reads below 3.0 V. 3.0 V is this family's figure; the Macintosh SE and Macintosh SE/30 use 2.8 V. To replace it, pull the old cell out of its holder and fit the new one with its "+" end matching the "+" on the logic board. Apple warns that the cell can explode if handled or discarded improperly, must not be recharged or shorted, and that a dead cell is hazardous waste.

The cell is lithium, so neutralise any leakage with a bicarbonate of soda solution, not vinegar; vinegar is for the alkaline 4.5 V pack in the Macintosh Plus and Macintosh 512K. Work with ventilation. Recap-a-Mac reports that the 1/2 AA cells fitted to the Classic spray electrolyte over the logic board, in some cases beyond repair, and advises changing an old cell straight away. Take the cell out of a machine going into storage. See Battery Explosion, Capacitor or Corrosion Damage.

Capacitors

Both logic boards use surface-mount electrolytic capacitors that leak, and the power/sweep board uses through-hole electrolytics. 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 power/sweep board exists in 110 V and 220 V versions. The primary reservoir is either CP1 and CP13 in series, two 220 µF 250 V capacitors, or, on some 220–240 V boards, a single 220 µF 400 V capacitor; Recap-a-Mac's 240 V board with the single capacitor is labelled 630-0525, the number Console5 gives for the two-capacitor board that BOMARC drew as 820-0525-A. Go by what is fitted before ordering; the capacitor guide shows how.

Power/sweep board

The Classic family has no separate analogue board or power supply. The power/sweep board carries the mains supply, the sweep circuits and the yoke, fan and hard-disk power connectors.

Rev. A and Rev. B boards are functionally equivalent but not interchangeable. A Rev. A board must be used with a Rev. A CRT yoke assembly; a Rev. B board with a Rev. B yoke and a Rev. B cover. Rev. A has plastic sleeves round the yoke connector prongs; on Rev. B the prongs are exposed.

Apple's Take Apart shows how to pull the fuse but prints no rating. The rating is on the board: "FP1 T3.15A/250V" on the 240 V board photographed by Recap-a-Mac, and GMA-3 or GMA-3.15 on BOMARC's drawings of boards 820-0395-A and 820-0525-A. Apple's next step after replacing the fuse is to replace the power/sweep board, so a fuse that blows again points to a fault on the board.

Recap-a-Mac lists cracked solder joints among this board's faults. Inspect the joints on the heavy parts and on the connectors whenever the board is out. The fan is a separate module; it comes out after the power/sweep board and is held to the chassis by two screws.

Rails

Apple publishes no rail voltages, no tolerances and no power-supply adjustment for these machines. The Service Source gives only the mains side (100–120 V AC, 47–63 Hz, 100 W maximum), and its Adjustments chapter covers light meter setup, video and yoke. The "+5 V 4.85–5.15 V / +12 V 11.90–12.75 V" pair quoted for compact Macs is Apple's Macintosh Plus procedure and does not apply here.

Measure at the logic board power connector and compare each rail with its nominal value and with a known-good machine. BOMARC's schematic of the Classic II logic board gives the pins: +12 V on pin 1, +5 V on pins 2 and 3, −12 V on pin 8, ground on pins 10–14. BOMARC's power/sweep board drawing shows −12 V on pin 8 and ground on pins 10, 11 and 14 of the same plug. On that drawing the +12 V rail comes from a 7812 regulator and −12 V from a 79L12, and the trimmer PP1, marked "VOLT ADJ" on 820-0395-A and "B+ adj" on 820-0525-A, sits in the switching supply's feedback network.

Video adjustments

Apple's adjustments are made from the rear, through the service door, with a mirror in front of the screen and the machine on for at least 30 minutes. Use a plastic alignment tool.

Classic / Classic II video controls and Apple's targets

Control	Designator	Apple's target
Contrast	PL2	40 foot-lamberts (± 3) on a full-brightness screen
Brightness	PL4	5 foot-lamberts (± 1) on a half-brightness screen
Horizontal size	LL2	Image 7 in (177.8 mm) wide
Vertical size	PF1	Image 4.7 in (119.38 mm) high
Vertical centring	PF2	Centred in the bezel
Horizontal centring	PL3	Centred in the bezel
Focus	PL1	Best overall focus

Targets and the PL2, PL4, LL2, PF1 and PF2 designators are from the Service Source; PL1 and PL3 are from the Service Guide. Tilt is corrected by rotating the yoke collar, with the power off while the clamp screw is tightened.

Memory faults that are not board faults

Apple's Sad Mac chart for these machines checks the memory configuration before the logic board:

• 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 Classic.
• On the Classic II, replace the 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.

Logic board notes

Classic

• 68000 at 7.8336 MHz, 512 KB ROM, 1 MB soldered RAM; expansion only through the optional memory expansion card, to 4 MB.
• One ADB port.
• Holding Command-Option-X-O at startup boots a System 6.0.3 disk held in ROM, a feature unique to the Classic. A machine that boots from it has a working logic board and display.

Classic II

• 68030 at 16 MHz on a 16-bit data path, 512 KB ROM, 2 MB soldered RAM plus two 30-pin SIMM sockets.
• No expansion slot. A microphone is fitted, which the Classic does not have.
• Apple's upgrade kit converted a Classic to a Classic II: a Classic II logic board, a Classic II rear housing, a microphone and an accessory kit. The original serial number was transferred to the new housing.

The Dead Mac Scrolls, the component-level reference for the earlier compact Macs, does not cover the Classic or Classic II.

Tools

• Long T15 Torx driver
• Case spreader
• CRT discharge tool
• Anti-static wriststrap
• Plastic hex alignment tool and a mirror, for video adjustments
• Multimeter
• Isopropyl alcohol, compressed air, soft brush

See Recommended Tools.

Related pages

• Macintosh Classic and Macintosh Classic II
• Macintosh Classic Capacitor Replacement Guide
• Macintosh Classic II Capacitor Replacement Guide
• Macintosh Classic / Classic II Troubleshooting
• Macintosh Classic/ Classic II/Performa 200 Service Source
• Macintosh Floppy Drive Maintenance
• CRT Discharge Procedure