RetroTechCollection

Macintosh IIsi Capacitor Replacement Guide

The Macintosh IIsi logic board and power supply contain surface-mount electrolytic capacitors that are prone to leakage after 30+ years of age. This guide provides detailed specifications and procedures for capacitor replacement ("recapping").

Why Recap?

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Electrolytic capacitors use a liquid or gel electrolyte that can leak over time due to:

  • Natural aging of the component sealing
  • Internal corrosion within the capacitor
  • Storage conditions (heat and humidity accelerate degradation)

The leaked electrolyte is both conductive and corrosive:

  • Conductive: Creates short circuits between traces, causing erratic behavior or complete failure
  • Corrosive: Eats through copper traces and attacks solder joints, potentially destroying the board beyond repair

Proactive recapping before leakage occurs will prevent irreversible damage.

Logic Board Capacitors

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The Macintosh IIsi logic board contains 13 electrolytic capacitors:[1]

Macintosh IIsi Logic Board Capacitor List
Quantity Capacitance Voltage Package Type Notes
2 220 µF 16V Axial electrolytic Main filter capacitors
11 47 µF 16V SMD electrolytic Surface-mount, prone to leakage
 
Macintosh IIsi logic board capacitor locations. Source: Recap-a-Mac

Replacement Options

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Electrolytic (Original Style)

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Spec Mouser Part Number Notes
220 µF 16V Axial Nichicon TVX1E221MAD Stock-like appearance
220 µF 16V Radial EPCOS B41828A5227M8 Lower cost alternative (mount flat)
47 µF 16V SMD Standard SMD electrolytic Available from various manufacturers

Tantalum (Recommended)

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Tantalum capacitors use a solid electrolyte that cannot leak, eliminating future leakage concerns:[2]

Spec Recommended Replacement Notes
47 µF 16V Tantalum SMD (AVX, KEMET, Vishay) Leak-proof; slightly larger footprint
220 µF 16V Tantalum axial or polymer electrolytic May need to adjust for size

Note: Tantalum capacitors are polarized and can fail catastrophically (short circuit) if installed backwards. Always verify polarity before soldering.

Polymer/Hybrid

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Modern polymer electrolytic capacitors offer:

  • No liquid electrolyte (won't leak)
  • Lower ESR than tantalum
  • Smaller size than tantalum equivalents

Panasonic OS-CON or similar polymer electrolytics are excellent choices where they fit.

Power Supply Capacitors

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The IIsi uses a Sony 160W power supply that also requires recapping. Warning: Power supplies contain high-voltage capacitors that can retain a lethal charge. Discharge all capacitors before servicing.

Known Power Supply Capacitors

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Power supply capacitor values may vary by PSU revision. Common values include:

Macintosh IIsi Power Supply Capacitors (typical)
Quantity Capacitance Voltage Package Type Location
2 470 µF 200V Radial Primary side (high voltage!)
1 2200 µF 25V Radial Secondary side
1 47 µF 100V Radial Secondary side
2 10 µF 25-50V Radial Various

Important: Always verify capacitor values against your specific unit before ordering. Some power supplies may have different revisions with different values.

Tools Required

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  • Soldering iron with fine tip (Hakko FX-600 or similar recommended)
  • Hot air rework station (for SMD removal)
  • Solder (60/40 or 63/37 leaded, 0.5-0.8mm)
  • Flux (no-clean or rosin)
  • Solder wick and/or desoldering pump
  • Isopropyl alcohol (>90%) and brushes for cleaning
  • Multimeter for testing
  • X-Acto knife blades for heat shielding

Removal Procedure

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Hot Air Method (Recommended)

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  1. Set hot air station to approximately 350-380°C, medium airflow
  2. Place X-Acto blades or metal shields around the capacitor to protect nearby plastic connectors
  3. Apply heat evenly around the capacitor until solder melts
  4. Use tweezers to lift the capacitor from the pads
  5. Repeat for all SMD capacitors

Soldering Iron Method

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  1. Apply flux to the capacitor terminals
  2. Heat one terminal while gently applying pressure to tilt the capacitor
  3. Alternate between terminals, rocking the capacitor until it releases
  4. Warning: This method risks pad lifting if too much force is applied

Twist-Off Method (Not Recommended)

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Some technicians grip the capacitor with pliers and twist to fatigue the terminals. This method:

  • Risks lifting pads from the PCB
  • May crack the board
  • Should only be used on boards that are already damaged

Cleaning

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After capacitor removal:

  1. Inspect pads for damage; repair lifted traces before proceeding
  2. Clean residue with isopropyl alcohol and a soft brush
  3. For heavy contamination, scrub with distilled water and dish soap
  4. Rinse with distilled water, then final rinse with isopropyl alcohol
  5. Allow to dry completely (24+ hours) before installing new capacitors

If corrosion has damaged traces:

  • Use a conductive trace pen for minor repairs
  • Solder jumper wires for major trace damage
  • Test continuity with a multimeter before reassembly

Installation

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Polarity

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Critical: Electrolytic and tantalum capacitors are polarized. Installing backwards will cause:

  • Immediate failure (electrolytics may bulge or pop)
  • Short circuit failure (tantalums can burn or catch fire)

The negative terminal is typically marked on the PCB with:

  • A filled-in side of the capacitor symbol
  • A stripe or bar on the silkscreen

On electrolytic capacitors, the negative terminal is marked with a stripe. On tantalum capacitors, the positive terminal is marked (stripe, bar, or "+").

Soldering SMD Capacitors

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  1. Tin one pad with fresh solder
  2. Hold the capacitor with tweezers, position on pads
  3. Tack one terminal by reheating the tinned pad
  4. Verify alignment, then solder the second terminal
  5. Reflow the first terminal with additional solder if needed
  6. Clean flux residue with isopropyl alcohol

Soldering Axial Capacitors

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  1. Insert leads through holes (or bend for surface mounting if holes are damaged)
  2. Verify polarity
  3. Solder both terminals
  4. Trim excess leads

Testing

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Before reassembling the Macintosh IIsi:

  1. Visual inspection — verify all capacitors are correctly oriented
  2. Continuity test — check that no solder bridges exist between pads
  3. Power-on test — with logic board outside case, briefly power on and verify operation
  4. Extended test — run the system for several hours to verify stability

Purchasing Kits

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Pre-made capacitor kits for the Macintosh IIsi are available from:

  • Console5 (console5.com)
  • ToTsRC/ToTsRETRO (totsrc.com)
  • Various eBay sellers

These kits typically include all logic board capacitors and sometimes power supply capacitors as well.

References

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  1. ↑ Caps! -- Macintosh IIsi, 68kMLA—link(accessed 2026-02-09)
  2. ↑ Recapping a Macintosh SE/30 and a IIsi, ED Retro Tech—link(accessed 2026-02-09)
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