Macintosh IIsi General Maintenance

Macintosh IIsi logic board 820-0301-A with every electrolytic marked: eleven 47 µF surface-mount parts and two 220 µF axials. Source: Recap-a-Mac.

This page covers routine care for the Macintosh IIsi.

Figures below come from Apple's Service Source for the IIsi and from Apple's Macintosh IIsi Developer Note, both hosted on this wiki.

What this machine is

Apple's specification for the Macintosh IIsi

Item	Figure
Processor	Motorola 68030 at 20 MHz, 32-bit internal data bus, 256-byte instruction and data caches, burst-mode RAM access, built-in MMU
Coprocessor	Motorola 68882 at 20 MHz — on the optional adapter card, not on the logic board
RAM	2 MB, expandable to 17 MB
ROM	512 K
PRAM	256 bytes
Expansion	One slot for either a NuBus or an 030 direct-slot card, 15 W maximum: +5 V 2.0 A, +12 V 175 mA, −12 V 150 mA
Sound	Output impedance 8–600 Ω, short-circuit protected, internal speaker disabled when a plug is inserted; four-voice wavetable synthesis and stereo sampling
Line voltage	100–240 VAC, automatically configured, 50–60 Hz
Maximum power	100 W, monitor excluded
Dimensions	4.0 × 12.4 × 14.9 in (10 × 31 × 37.2 cm), 10 lb (4.5 kg)

All of that is Apple's. The odd 17 MB ceiling is not a misprint — the IIsi has 1 MB soldered to the board plus four SIMM sockets.

The FPU lives on the adapter card. Apple's specification is explicit: the 68882 is "included on the optional adapter card". A IIsi with no card fitted has no floating-point unit, and pulling the logic board apart looking for an empty FPU socket is wasted effort.

The adapter card is also how the slot works. The IIsi's single slot takes either a NuBus card or an 030 direct-slot card, and which one depends on which adapter is fitted. Apple's take-apart procedure removes the adapter card, the direct-slot card and the plastic bracket as one assembly, then pulls the adapter and the card off the logic board together.

Power supply

Apple service part 661-1616; the logic board is 661-1615 and the fan a separate assembly, 810-6030. Apple rates the machine at 100 W maximum, monitor excluded.

The unit itself is a Sony APS-06M. That matters when you come to recap it, because two of its capacitors are the dangerous ones:

• C101 and C102, 220 µF 250 V. These are in series across the rectified mains — that is how a universal-input supply holds off the ~340 V that 240 V mains rectifies to, on parts rated 250 V each. Replace both together with matched parts. Never fit a single capacitor in place of the pair, and do not substitute a lower voltage rating.
• C105, 4.7 µF 400 V, also on the primary side.

There is a daughtercard inside the supply carrying two surface-mount capacitors — 100 µF 6.3 V and 33 µF 25 V — and they leak. They are easy to miss because they are not on the main board of the supply.

Full list and procedure: Macintosh IIsi Capacitor Replacement Guide.

There is no published figure of 160 W for this supply. Apple's own maximum-power specification for the machine is 100 W.

What Apple does and does not publish

Apple publishes no rail tolerance and no power-supply adjustment procedure for the Macintosh IIsi. The Service Source contains no acceptable-range table for any rail and no trimmer adjustment; every power fault in the symptom charts ends in "Replace power supply". The "+5 V 4.85–5.15 V / +12 V 11.9–12.7 V" table that circulates on pages of this era is Apple's Macintosh Plus procedure — genuine there, where it uses voltage test cable 077-0135 on the external floppy port — copied onto machines it was never written for. It has been removed from this page rather than reproduced, and no substitute has been invented.

What you can do instead is compare against a known load. Each rail at the logic-board power connector should sit close to its nominal value with the machine running and should not move when a drive spins up. A rail that is visibly low, or that sags under load, points at the supply. A rail that measures as a short to ground with the supply disconnected points at the logic board.

Before you open it

You are allowed to recap this supply, and it is one of the parts most likely to have failed. Understand what is live in it first: with the cover off and the lead plugged in, the fuse, input filter, bridge rectifier and the 250 V pair sit at mains potential, and that pair holds a charge after the plug comes out. Unplug, discharge each capacitor through a 1 kΩ / 5 W resistor, and confirm with a meter that it reads near zero before a tool goes near the primary side.

Battery

A 3.6 V lithium half-AA cell in a holder on the logic board keeps the real-time clock and parameter RAM alive with the machine unplugged.

Apple's check is a measurement, not a calendar. Set a meter to the 10 V DC range, put the positive probe on the positive end of the cell and the negative probe on the negative end, and replace the cell if it reads below 3.0 V. Apple publishes no replacement interval, and none is invented here: a cell above 3.0 V is doing its job and one below it should come out today whatever its age.

3.0 V is what Apple's manual for this machine says. It is not the 2.8 V of the IIcx, IIci and Quadra 700, and not the 3.2 V of the Centris and larger Quadras. These thresholds are machine-specific and get transplanted between pages; use the one from your own machine's manual.

If it has leaked

This is a lithium cell, so neutralise with bicarbonate of soda, not vinegar. Vinegar is the right treatment for alkaline leakage, which is basic; it is the wrong treatment here and it adds water and chloride to an already corroded board. Use a paste of sodium bicarbonate and distilled water, rinse with distilled water, follow with isopropyl alcohol and dry thoroughly.

Then check the damage rather than assuming there is none:

• Inspect under magnification for traces that have gone dull, green or thin.
• Buzz out every track running away from the holder — corrosion travels under the solder mask and does not show from above.
• Check the underside of the board. Electrolyte wicks down through vias.

See Battery Explosion, Capacitor or Corrosion Damage and Battery Refurbishment.

Take the cell out before the machine goes into storage. That is not a service interval; it is the one measure that reliably prevents this damage.

Connectors and sockets

Oxidised contacts cause more intermittent faults on a machine this age than failed silicon does, and they are the cheapest thing to put right.

• SIMM sockets. Clean with isopropyl alcohol on a swab and reseat. Do not take an abrasive to a module's gold fingers — once you are through the plating, the base metal oxidises and then transfers to every socket the module touches.
• VRAM sockets. Same treatment. Video faults that come and go when the case is knocked usually start here.
• NuBus and PDS slots. Inspect for bent contacts and debris before a card goes home; check the card's edge fingers too.
• ROM SIMM socket, where one is fitted. A poorly seated ROM gives a machine that chimes and does nothing else.
• Logic-board power connector. Look for browning or a distorted housing. A discoloured power connector is a warning, not a cosmetic problem.
• ADB, serial, SCSI and floppy connectors. Reseat; check ribbon cables for cracked conductors where they fold.

A contact cleaner such as DeoxIT D5 earns its place on genuinely corroded contacts. It is not a preventive treatment and it does not belong on clean gold.

The speaker contacts

The IIsi's mono loudspeaker sits on a small assembly underneath the logic board and is reached only after the cover, adapter card, fan, power supply, hard drive and logic board have come out — Apple lists all six as preliminary steps. The connection is by spring contact rather than a plug, and tarnished contacts give intermittent or absent internal sound while the headphone jack stays perfect.

That combination — headphone jack fine, internal speaker dead or cutting out — is the signature. Clean the spring contacts and the matching pads, check the springs still have tension, and make sure the assembly is seated before the board goes back.

The fan

The fan is a separate assembly. Apple's removal instruction is exactly as blunt as it sounds: grip the fan and pull up, using some force, until it snaps out. It goes back the same way.

The IIsi is a quiet machine and people sometimes assume it is convection-cooled. It is not — there is a fan, and it should be turning.

Capacitors

Thirteen electrolytics on logic board 820-0301-A: eleven 47 µF 16 V surface-mount and two 220 µF 16 V axial. MacDat and Console5 agree on that complement, and Recap-a-Mac's annotated photograph of the board is hosted here as File:Mac IIsi Recap Guide.jpg.

Designators and procedure: Macintosh IIsi Capacitor Replacement Guide.

Apple published no component-level capacitor data for any Macintosh of this era, so these are community readings of physical boards. Read the value off each can before you lift it.

Cleaning

Opening the case

The IIsi's cover releases with clips and latches — no tools and no screws.

Inside

• Compressed air and an anti-static brush on the logic board, the supply and the fan. Hold the fan blade still while you blow it: spinning a fan with compressed air drives it as a generator and puts a reverse voltage back down its cable.
• Isopropyl alcohol (99 %) and a soft brush for grime, working outwards from each capacitor and from the battery holder.
• Check the underside of the board as well as the top. Both battery and capacitor electrolyte travel through vias.

Outside

• A damp microfibre cloth and mild detergent. No abrasives, no solvents — the texture on these shells does not survive either.
• ADB keyboards come apart for washing: keycaps off, warm soapy water, dry them completely, then clean the contacts with isopropyl alcohol.
• Mouse ball out, rollers scraped and wiped with isopropyl alcohol.

The platinum-grey plastics yellow with age. The discolouration is in the body of the plastic rather than on the surface, so cleaning will not shift it; see Retrobrite for what can be done and what it costs in brittleness.

Heavily contaminated boards can be washed, but do it properly: distilled water, a soft brush, a thorough rinse in more distilled water, then isopropyl alcohol to displace it, then a full day drying in a warm draught with the battery out. A half-dried board fails in ways that are much harder to diagnose than the dirt was.

Floppy drive

The 1.4 MB Apple SuperDrive is direct drive. It has no belt. Advice to fit a new belt to a sluggish or non-ejecting SuperDrive — including to the auto-inject version — is wrong: there is nothing there to replace. What these drives actually suffer is hardened grease on the head carriage and eject rails, dust in the mechanism, and dirty or worn heads. On manual-inject drives a worn eject gear is a genuine and common failure.

• Clean the heads with isopropyl alcohol on a lint-free swab, supporting the upper head arm so it is not sprung.
• If the rails are stiff, re-lubricate with a silicone grease — not white lithium grease, which gums up as it ages.
• If a disc will not eject, hold the mouse button down while switching the machine on to run a full eject cycle before taking anything apart.

See Macintosh Floppy Drive Maintenance.

Hard disk

The original SCSI mechanisms are past thirty years old and the usual failures are a stuck spindle, dried head-park grease and dead controller electronics. Solid-state replacements — BlueSCSI, ZuluSCSI, SCSI2SD — are quieter, cooler and considerably more reliable, and they let you keep the original drive on a shelf.

Whatever you fit, get the termination right: the drive at the end of the internal bus must be terminated, and the computer itself is always SCSI ID 7. See Macintosh HDD Maintenance.

Storage

• Take the battery out.
• Store dry and at room temperature — not a loft, not a garage.
• If the logic board comes out, bag it anti-statically and lay it flat.
• Nothing needs periodic running. "Power it up every few months to keep the capacitors formed" is repeated widely and supported nowhere for machines of this kind. The real hazard to a stored Macintosh is the cell in the battery holder, and removing it costs nothing.

Related pages

• Macintosh IIsi
• Macintosh IIsi Capacitor Replacement Guide
• Macintosh IIsi Troubleshooting
• Macintosh IIsi Service Source
• Macintosh IIsi Developer Note
• Retrobrite
• Recommended Tools