Macintosh SE General Maintenance

Macintosh SE Interior

This page covers cleaning, the PRAM battery, connector corrosion, the parts that actually fail and what can and cannot be adjusted on the Macintosh SE.

The SE contains a CRT. Read CRT Discharge Procedure before opening the case. Apple's instruction is to discharge the CRT to the ground lug before disconnecting anything — failing to do so can damage the logic board or the analogue board — and never to fit a grounding wriststrap until after the CRT has been discharged.

How the SE is built

The SE is not built like a Macintosh Plus, and repair information written for the Plus does not transfer. Inside the SE there are three separate assemblies behind the CRT, not one:

• the analogue board, carrying the sweep and CRT drive circuitry and the brightness control;
• a separate power supply module, secured to the analogue board by four screws and joined to it by the power supply cable;
• a separate video board on the neck of the CRT.

Apple's take-apart sequence separates all three, and the power supply can be replaced without replacing the analogue board. Apple's symptom charts treat them as distinct too: a completely dark screen with a dead fan calls for the power supply first and the analogue board second.

The SE also has a cooling fan, which the Plus does not.

Regular cleaning

Internal

• Unplug the machine and discharge the CRT first.
• Compressed air or an anti-static brush for dust on the analogue board, logic board and fan housing.
• Isopropyl alcohol (>90 %) and a soft ESD-safe brush for grime.
• A distilled water wash is acceptable for a badly contaminated board provided it is dried completely before power is applied.

External case and CRT

• Damp microfibre cloth and mild soap on the plastics; no abrasives.
• Glass cleaner onto the cloth, not onto the screen.
• Isopropyl alcohol for adhesive residue and heavy staining.

Keyboard and mouse

• Remove the mouse ball and clean the rollers.
• Compressed air under the keys; keycap puller only if a deeper clean is needed.

PRAM battery

The Macintosh SE keeps its parameter memory in a CMOS custom chip backed by a lithium battery — Apple quotes a seven-year life. It is a 3.6 V half-AA lithium cell.

Two types of board exist and they are handled differently:

• On solder-type boards the cell is soldered in. Apple's method is to cut the leads at both ends as close to the board as you can without touching the board, and to fit the replacement into the extra set of mounting holes just inside the original ones.
• On later boards the cell sits in a holder and simply pulls out.

Whichever type you have, orient the replacement so that the end marked "+" matches the "+" on the logic board.

Apple's replace-below threshold for the SE is 2.8 V, measured across the cell with the meter on its 10 V DC range and the logic board removed. That figure is specific to this machine — the Macintosh Classic and Macintosh Classic II use 3.0 V, and other Macintosh families use others again. Do not transplant a threshold between models.

This cell is lithium, not alkaline. Lithium-thionyl-chloride leakage is not neutralised with vinegar; use a bicarbonate of soda solution, then an isopropyl alcohol rinse, and work in ventilation — these cells can vent sulphur dioxide. The vinegar method belongs to the alkaline 4.5 V cell in the Macintosh Plus and the Macintosh 128K/512K. See Battery Explosion, Capacitor or Corrosion Damage.

Remove the cell if the machine is going into storage. The SE runs without it.

Connector and socket corrosion

Worth inspecting and reseating:

• logic board cable to the analogue board (J12 at the logic board end)
• floppy and SCSI connectors
• CRT yoke cable and video board
• speaker and fan leads
• the PDS slot, if a card is fitted

Contact cleaner and a reseat restores most intermittent faults. Socketed ROM and RAM oxidise too; reseating them is the first move on a Sad Mac or a no-boot. Apple's chart for a Sad Mac also says to check that the three-pin memory jumper is configured correctly before blaming the board. See Sad Mac Error Codes and the Sad Mac Decoder.

What actually fails

The Dead Mac Scrolls gives component-level data for the SE analogue board that is still the best published source for it.

• Herringbone pattern across the whole display, machine otherwise usable — early SE analogue boards. The fix is to replace the original flyback transformer, Apple part 157-0042A at board reference T2, with the later 157-0042C.
• Excessively loud, display jitters and shakes — the original crossflow fan at board reference B1. Apple itself notes that later replacement fans differ from the original. A brushless 12 V DC fan is the usual substitute.
• No startup bong, dark screen, a hissing or sizzling noise — check the barrel rectifier at board reference CR2; a shorted device reads near zero ohms.
• No startup bong, dark screen, no noise at all — check the barrel rectifier at CR3, the horizontal output transistor at Q2, and then the flyback at T2.
• Cracked solder joints around the flyback, the yoke connector, the regulator heatsinks and the power input section produce intermittent, flickering or dropped-out video. Reflow properly with added solder.

Electrolytic capacitors on both boards cause unstable power, geometry distortion and audio problems; the values are on the Macintosh SE Capacitor Replacement Guide, and Capacitor Failure Symptoms covers the general pattern.

Working on the power supply means working on mains-derived voltages and a charged reservoir capacitor: it is a recappable assembly like any other, but treat the primary side as live until you have measured it as discharged.

Logic board identification

Two exchange logic boards existed. Apple's rule: a battery in a holder means board 661-0536; a soldered battery means 661-0526, and if the disk controller is a SWIM (part number 344-0062) rather than an IWM, the customer's SWIM and ROMs move across to the replacement board. The Dead Mac Scrolls identifies the two bare boards as 820-0176 (original) and 820-0250 (DIP SIMM).

Power rails: what Apple publishes

Apple publishes no rail tolerance and no power-supply adjustment procedure for the Macintosh SE. The Adjustments chapter of the Macintosh SE Service Source contains yoke and video procedures only, and the Specifications chapter gives the mains side alone — line voltage 90–140 V AC or 170–270 V AC, 47–63 Hz, 100 W maximum.

There is no trimmer to set the +5 V rail on this machine. The adjustment sometimes described as "R56" belongs to the Macintosh 128K/512K/Plus power/sweep board, which the SE does not have; the Plus procedure and its 4.85–5.15 V / 11.90–12.75 V window are published for that board and not for this one.

What you can still do with a meter:

• Measure at the floppy power connector, the hard disk power connector and the logic board power connector.
• 5 V logic is specified for a 5 V supply at ±5 per cent, so 4.75–5.25 V is a reasonable go/no-go; treat anything outside it as a fault.
• A rail that sags under load, or that carries visible ripple on a scope, is a fault whatever the DC reading says.
• Compare against a known-good machine of the same model where you can.

If the rails are wrong, the suspects are the electrolytics, the solder joints in the power supply and the rectifiers listed above — not a nonexistent trimmer.

Related pages

• Macintosh SE
• Macintosh SE Capacitor Replacement Guide
• Macintosh SE Memory Upgrade Guide
• Macintosh SE Troubleshooting
• CRT Discharge Procedure
• Recommended Tools