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Macintosh IIsi Capacitor Replacement Guide

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The Macintosh IIsi has aluminium electrolytic capacitors on the logic board and in the power supply, and Recap-a-Mac found leaks in both; it describes the supply as "extremely prone to leakage" and expects few to still be working on their original capacitors.[1][2] Apple published no capacitor lists for either board; the lists below are from Console5 and Recap-a-Mac, who worked from physical boards.

Signs of failure

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  • Brown or crusty residue around the surface-mount capacitors, and corrosion on nearby pads and tracks.[3]
  • Electrolyte marks on the power supply board around the secondary capacitors.[3]
  • For the symptoms of failed capacitors see Capacitor Failure Symptoms; for Apple's fault charts see Macintosh IIsi Troubleshooting.

Logic board capacitor list

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Macintosh IIsi logic board 820-0301-A with the electrolytic capacitors marked (Recap-a-Mac)
Macintosh IIsi logic board 820-0301-A
Positions Value Type
C7, C9, C10, C11, C20, C22, C31, C34, C35, C36, C38 47 µF 16 V Surface-mount electrolytic
C45, C130 220 µF 16 V Axial electrolytic

Designators are Console5's; its list names C31 twice.[4] Recap-a-Mac's photograph shows the same eleven 47 µF and two 220 µF parts.[1] Its board has the ROM soldered on; Apple's developer note says the first production boards carried the ROM on a ROM SIMM instead.[5] Recap-a-Mac warns that a board may not look identical to its photograph, which also has a replacement CPU and some capacitors moved off damaged pads.[1] A higher voltage rating in the same size is acceptable. Ed Retro Tech replaced the surface-mount parts with tantalums, which have a solid electrolyte and cannot leak; mind the polarity marking, which on a tantalum marks the positive end.[3]

Power supply capacitor list

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Macintosh IIsi power supply (Sony APS-06M) and its control board with the electrolytic capacitors marked (Recap-a-Mac)
Sony APS-06M (Macintosh IIsi power supply)
Position Value Notes
C101, C102 220 µF 250 V Primary side. Recap-a-Mac: should not normally need replacing
C105 4.7 µF 400 V Primary side
C106 100 µF 10 V
C201, C202 2200 µF 6.3 V
C203, C212 1200 µF 16 V
C221, C222 220 µF 16 V
C302 56 µF 35 V 47 µF on some revisions (Console5)
C401 100 µF 25 V
C402 47 µF 25 V
Control board 33 µF 25 V Surface-mount
Control board 100 µF 6.3 V Surface-mount

Positions are Console5's, and the values agree with Recap-a-Mac's photograph.[6][2] The two control-board parts are easy to miss because they are not on the main board of the supply.

The supply works from rectified mains, and C101 and C102 hold a charge after it is unplugged. Discharge them and confirm with a meter before working on the primary side. Fit replacements of at least the original voltage rating.

Procedure

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Apple's take-apart order for the logic board is cover, adapter card, fan, power supply, then the board itself.[7]

  1. Remove the cover: push down on the small tabs with your thumbs while lifting the large tabs with your forefingers. It may snap loudly.[7]
  2. Remove the adapter card and any expansion card: pull straight up on the adapter.[7]
  3. Remove the fan: put your thumbs under it and pull up firmly until it snaps free.[7]
  4. Remove the power supply: press the two metal tabs near its rear and lift it about half an inch, then pull the silver tab towards the floppy drive while lifting the supply out.[7]
  5. Disconnect the hard drive power, hard drive data and floppy cables from the logic board.[7]
  6. With the rear of the case towards you, release the two tabs with your forefingers while pushing on the 120-pin connector with your right thumb, and slide the board forward until it stops.[7]
  7. Lift the board out once the power button clears the rear panel. Do not touch connectors J19 and J20; Apple warns that skin oil harms them.[7]
  8. Photograph the board and note the polarity of every capacitor before removing any.[3]
  9. Remove the old capacitors with hot air, shielding nearby plastic connectors; Ed Retro Tech used craft-knife blades held with springs.[3]
  10. Clean the board: scrub with distilled water and a little soap, rinse with isopropyl alcohol and let it dry for at least 24 hours.[3]
  11. Prepare the pads, fit the new capacitors observing polarity, and inspect for bridges before reassembly.[3]
  12. When refitting the board, make sure the speaker's metal fingers touch the contacts on the underside of the logic board.[7]

The supply comes apart in the same way for its own recap; Ed Retro Tech's article shows the board out of its case and cleaned.[3]

After the recap

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Check that the machine starts from the keyboard power key and switches off from Shut Down; both go through the soft-power circuit.[8] Apple publishes no rail tolerances for the IIsi supply; if it will not start, work through the power entries in Macintosh IIsi Troubleshooting.[7]

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References

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  1. ↑ 1.0 1.1 1.2 Macintosh IIsi, Recap-a-Mac—link(accessed 2026-09-30) Annotated photograph of logic board 820-0301-A, hosted here as File:Mac IIsi Recap Guide.jpg: 11 × 47 µF 16 V surface-mount and 2 × 220 µF 16 V axial. The photographed board has a replacement CPU and some replacement capacitors placed off their original pads.
  2. ↑ 2.0 2.1 Macintosh IIsi Power Supply, Recap-a-Mac—link(accessed 2026-09-30) Annotated photograph of the Sony APS-06M supply and its control board, hosted here as File:Mac IIsi Power Supply Recap Guide.jpg.
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 Recapping a Macintosh SE/30 and a IIsi logic boards and the IIsi power supply, Ed Retro Tech, 2020-12-08—link(accessed 2026-09-30) Photographs of a leaking IIsi power supply and logic board; capacitors removed with a hot-air station, nearby plastic parts shielded with craft-knife blades; board scrubbed with distilled water and soap, rinsed with isopropyl alcohol and dried for at least 24 hours; tantalum replacements on the logic board.
  4. ↑ Macintosh IIsi, Console5 TechWiki—link(accessed 2026-09-30) Logic board 820-0301-A: C7, C9, C10, C11, C20, C22, C31 (listed twice), C34, C35, C36, C38 47 µF 16 V; C45, C130 220 µF 16 V. Power supply: Sony APS-06M.
  5. ↑ Apple Computer, Macintosh IIsi Computer Developer Note (1990), File:Macintosh IIsi Developer Note.pdf, ROM interface, PDF p. 38: first production units use a 512 KB ROM SIMM; later units have the ROM soldered to the logic board.
  6. ↑ Sony APS-06M, Console5 TechWiki—link(accessed 2026-09-30) C101, C102 220 µF 250 V; C105 4.7 µF 400 V; C106 100 µF 10 V; C201, C202 2200 µF 6.3 V; C203, C212 1200 µF 16 V; C221, C222 220 µF 16 V; C302 56 µF 35 V (47 µF on some revisions); C401 100 µF 25 V; C402 47 µF 25 V; riser board 33 µF 25 V (polymer in the kit, because of damage from neighbouring electrolytics) and 100 µF 6.3 V.
  7. ↑ 7.00 7.01 7.02 7.03 7.04 7.05 7.06 7.07 7.08 7.09 Apple Computer, Macintosh IIsi Service Source (1995), File:Macintosh iisi.pdf; see Macintosh IIsi Service Source. Take Apart, PDF pp. 30-45: cover p. 30; fan pp. 31-32; power supply pp. 33-34; logic board pp. 41-45.
  8. ↑ Apple Computer, Macintosh IIsi Computer Developer Note (1990), File:Macintosh IIsi Developer Note.pdf; see Macintosh IIsi Developer Note. PDF pp. 64-65: soft power control, +5 V trickle output, software shutdown.


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