Macintosh IIsi
The Macintosh IIsi is a more consumer-oriented Mac II that was released in 1990.
Specifications
| Spec | Details |
|---|---|
| Release Date | October 1990 |
| Discontinuation Date | March 1993 |
| Processor | Motorola 68030 @20MHz FPU: Optional Bus Speed: 20MHz |
| RAM | 4x 30-pin SIMM Slots - 2, 3, or 5MB Standard - 65MB Maximum |
| Hard Disk | 3.5" SCSI - 40, 80, or 160MB Standard |
| Graphics | 64-320KB VRAM (shared with system RAM) |
| Audio | Internal Speaker |
| Internal Drives | 1x Auto-inject 3.5" 1.44MB Floppy Drive |
| Expansion | 1x PDS Slot (adaptable to NuBus) |
| Networking | None |
| Other I/O | - 1x ADB - 2x Serial - 1x DB25 SCSI - 1x DB15 Video Out - 1x DB19 External FDD Port - 1x Line Out - 1x Line In |
| PRAM Battery | 1/2AA Lithium 3.6V |
| Original Mac OS | System 6.0.7 |
| Maximum Mac OS | Mac OS 7.6.1 |
Upgrades
CPU Upgrade
68040 CPU upgrade cards were available.
SSD Upgrade
Check our page on SCSI SSD replacements for more info.
Resources
 Service Manual |
 Logic Board Schematic |
Capacitor Reference |
|---|
Common Faults & Maintenance
PRAM Battery Leaks
The Macintosh IIsi's PRAM battery is very prone to leaking, and should always be removed if original.
Capacitors
The IIsi motherboard uses many surface mount electrolytic capacitors, which always leak with age, causing corrosion to the motherboard. They must be replaced for reliable operation.
The IIsi's Sony power supply also must be recapped, as the ELNA Low ESR capacitors inside it leak very badly.
Other Notes
Most original SCSI hard drives for these have gone bad, especially those made by Quantum, which suffer from sticky rubber bumpers in the head assembly.
The floppy drives in these often suffer from eject motor failures due to a gear that falls apart with age. This gear can be replaced without too much trouble.
The Mac IIsi's case yellows with age. A retrobrite process can be used to correct this, if it bothers you. The plastic is not nearly as brittle as Macs from the 90s though.
Page last updated (MM/DD/YYYY): 03/03/2025
Update Reason: page rewritten
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