Macintosh IIsi General Maintenance
Routine care for the Macintosh IIsi, a 1990 desktop now more than thirty years old. The parts that need attention are the lithium battery, the capacitors on the logic board and in the power supply, and the spring contacts of the speaker. The procedures below are Apple's, from the IIsi Service Source, unless another source is named.[1]
Reference figures
[edit | edit source]| Item | Figure |
|---|---|
| Battery | 3.6 V lithium; replace below 3.0 V[1][2] |
| Mains input | 100-240 V AC, automatic; 50-60 Hz; 100 W maximum excluding the monitor (Service Source); 160 W, 1.33 A (Apple specification sheet)[1][2] |
| Expansion slot | 15 W maximum[1] |
| ADB port | +5 V on pin 3, protected by a 1 A fuse[3] |
| RAM | Four identical 30-pin SIMMs, 100 ns or faster, in bank B; 1 MB soldered in bank A[3][2] |
| Part numbers | Logic board 661-1615; power supply 661-1616; fan assembly 810-6030; adapter card and bracket 815-6246; speaker/LED assembly 810-6031; floppy drive 661-0474[1] |
Opening the case
[edit | edit source]The IIsi has no case screws. Push down on the small tabs with your thumbs and at the same time lift the large tabs with your forefingers; the cover may come off with a loud snap.[1] Everything inside is held by clips and tabs, and Apple's take-apart order is cover, adapter card, fan, power supply, drives, logic board, then the speaker underneath.[1]
Battery
[edit | edit source]The clock and parameter RAM are kept by a 3.6 V lithium cell in a holder on the logic board.[2] To check it, remove the cover, set the meter to the 10 V DC range, put the probes on the ends of the battery and replace it if it reads below 3.0 V.[1] To replace it, remove the cover and the expansion card, prise open the latch at the end of the holder with a small flat-blade screwdriver, lift off the cover and take the cell out. Match the "+" end of the new cell to the "+" on the holder.[1] For "clock not running", Apple's cures are the battery, then resetting PRAM, then the logic board.[1]
The clock and PRAM are kept alive by the power supply's +5 V trickle output or by the battery, so they run from the trickle supply whenever the IIsi is plugged in.[3]
Take the cell out before storing the machine. If it has leaked, neutralise the residue with bicarbonate of soda (vinegar is for alkaline cells), rinse, dry with isopropyl alcohol, and check the tracks around the holder on both sides of the board. See Battery Explosion, Capacitor or Corrosion Damage and Battery Refurbishment.
Power supply
[edit | edit source]The supply is Apple part 661-1616, a Sony APS-06M.[1][4] Recap-a-Mac calls it "extremely prone to leakage" and says recapping it is a necessity; the capacitor list is on the Macintosh IIsi Capacitor Replacement Guide.[5] To remove it, take out the cover, expansion card and fan, press the two metal tabs near the rear of the supply and lift it about half an inch, then pull the silver tab towards the floppy drive and lift the supply out.[1]
The supply is never fully off while it is plugged in: it keeps a +5 V trickle output for the soft-power circuit, and its primary capacitors (C101 and C102, 220 µF 250 V) hold a charge after it is unplugged. Unplug it, discharge the primary capacitors and confirm with a meter before working on it.[3][4]
Apple publishes no rail tolerances and no adjustment for this supply. Its symptom charts end every power fault at "replace power supply". For a screen that is completely dark with the fan off, the first steps are to remove the NuBus card (Apple notes that the card "draws more than 45 watts") and the peripherals and switch on again.[1]
Fan
[edit | edit source]The fan is a separate assembly (810-6030). Remove the cover and expansion card, put your thumbs under the fan and pull up firmly until it snaps free.[1] For intermittent shutdowns Apple's first cure is to clear the vents on the back and top of the case: the thermal protection may have shut the machine down, and it should run again after 30 to 40 minutes.[1]
Speaker contacts
[edit | edit source]The speaker and LED assembly sits in the bottom of the case, under the logic board, and connects through metal fingers that press against contacts on the underside of the board.[1] When those contacts tarnish, the internal speaker cuts out, sometimes only after the machine has run for hours, while the headphone jack still works. The Macintosh hardware FAQ's fix is to take the speaker assembly out, clean the contacts with isopropyl alcohol and, if wanted, treat them with a contact preservative such as DeoxIT.[6]
Apple's order to reach it: cover, adapter card, fan, power supply, hard drive and logic board out; push the LED out of its holder and free its cables from the two cable holders; release the four clips and lift the speaker out. When refitting, check that the speaker's metal fingers touch the contacts on the underside of the logic board.[1]
Logic board and connectors
[edit | edit source]To remove the board, disconnect the hard drive power, hard drive data and floppy cables; with the rear of the case towards you, release the two tabs while pushing the 120-pin connector with your right thumb; slide the board forward until it stops and lift it out once the power button clears the rear panel. Do not touch connectors J19 and J20 while handling the board, because skin oil harms them. Move the SIMMs to the replacement board.[1]
The SIMMs go in as a set of four identical modules.[2] The first production boards carry the ROM on a ROM SIMM, and on those boards the SIMM must be present; later boards have the ROM soldered.[3][7] The rear power switch can be locked on with a coin or screwdriver; for a IIsi that restarts itself, Apple's cure is to turn that switch to the unlocked, horizontal position.[3][1]
Drives
[edit | edit source]- The internal 1.4 MB floppy drive comes out after its cable is disconnected and its two tabs are released. Apple recommends a dust shield on the SuperDrive, and a drive must be cleaned before one is fitted. If a disk will not eject, switch off and hold the mouse button down while switching on; then eject it manually.[1] See Macintosh Floppy Drive Maintenance.
- The hard drive lifts out in its carrier after the two tabs are released. The internal drive must carry a terminator, and an external SCSI device must use a different ID.[1] See Macintosh HDD Maintenance.
Capacitors
[edit | edit source]Logic board 820-0301-A has eleven 47 µF 16 V surface-mount electrolytics and two 220 µF 16 V axials, and Recap-a-Mac found leaking capacitors on both the logic board and the supply.[8] Designators and procedure are on the Macintosh IIsi Capacitor Replacement Guide.
Related pages
[edit | edit source]- Macintosh IIsi
- Macintosh IIsi Capacitor Replacement Guide
- Macintosh IIsi Troubleshooting
- Macintosh IIsi Service Source
- Macintosh IIsi Developer Note
- Recommended Tools
References
[edit | edit source]- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 1.18 1.19 1.20 Apple Computer, Macintosh IIsi Service Source (1995), File:Macintosh iisi.pdf; see Macintosh IIsi Service Source. Page numbers are the PDF's: Specifications pp. 5-12; Symptom Charts pp. 15-28; Take Apart pp. 30-48; adapter cards pp. 50-56; Battery Verification p. 59; Battery Replacement pp. 60-62; Exploded View p. 64.
- ↑ 2.0 2.1 2.2 2.3 2.4 Macintosh IIsi: Technical Specifications, Apple—link(accessed 2026-09-30) Battery 3.6 V lithium; max watts 160, 1.33 A; soft power and pass-through outlet; four 30-pin SIMM slots installed in groups of four, 100 ns.
- ↑ 3.0 3.1 3.2 3.3 3.4 3.5 Apple Computer, Macintosh IIsi Computer Developer Note (1990), File:Macintosh IIsi Developer Note.pdf; see Macintosh IIsi Developer Note. PDF pp. 32-38 (RAM, ROM SIMM), pp. 62-66 (ADB connector, RTC and PRAM, soft power, trickle supply, power switch lock, reset).
- ↑ 4.0 4.1 Sony APS-06M, Console5 TechWiki—link(accessed 2026-09-30)
- ↑ Macintosh IIsi Power Supply, Recap-a-Mac—link(accessed 2026-09-30)
- ↑ 32 How can I fix the sound on my IISI?, TULARC—link(accessed 2026-09-30)
- ↑ Mac IIsi, Low End Mac—link(accessed 2026-09-30)
- ↑ Macintosh IIsi, Recap-a-Mac—link(accessed 2026-09-30)