Macintosh 128K/512K Capacitor Replacement Guide
Replacing electrolytic capacitors (recapping) in your Macintosh 128K and 512K is essential for long-term reliability. Over time, capacitors degrade, leading to voltage instability, display artifacts, and system failure. Proactively replacing these components ensures continued functionality and prevents potential board damage.
Capacitor Inspection
[edit | edit source]Before replacing capacitors, carefully inspect them for deterioration. Common failure symptoms include:
- Bulging Tops – A properly functioning capacitor has a flat top. Swelling or doming indicates failure.
- Leaking Electrolyte – Brown or white crust around capacitor leads signals internal leakage.
- Corrosion – PCB staining or green residue near the base of a capacitor suggests corrosion.
If any of these symptoms are present, replacement is highly recommended.
Macintosh 128K/512K Capacitor List
[edit | edit source]The Macintosh 128K and 512K analog board and logic board contain electrolytic capacitors that should be replaced proactively. Below are verified capacitor specifications for both boards.
Analog Board Capacitors
[edit | edit source]| Label | Capacitance | Voltage | Quantity |
|---|---|---|---|
| C1 | 3.9µF | 35V | 1x |
| C2 | 4700µF | 16V | 1x |
| C3 | 220µF | 16V | 2x |
| C5 | 47µF | 10V | 1x |
| C6 | 22µF | 50V | 2x |
| C10 | 33µF | 16V | 2x |
| C11 | 10µF | 160V | 1x |
| C12 | 22µF | 50V | 2x |
| C18 | 33µF | 16V | 2x |
| C24 | 2200µF | 16V | 4x |
| C27 | 2200µF | 16V | 1x |
| C28 | 1000µF | 16V | 1x |
| C30 | 2200µF | 16V | 1x |
| C31 | 220µF | 16V | 1x |
| C32 | 2200µF | 16V | 1x |
| C33 | 4700pF | 250V | 2x |
| C34 | 100µF | 200V | 4x |
| C35 | 100µF | 200V | 1x |
| C36 | 4700pF | 250V | 1x |
| C37 | 0.47µF | 250V | 1x |
| C38 | 100µF | 200V | 1x |
| C39 | 100µF | 200V | 1x |
| C42 | 470µF | 10V | 2x |
| C45 | 470µF | 10V | 1x |
Logic Board Capacitors
[edit | edit source]| Label | Capacitance | Voltage | Quantity |
|---|---|---|---|
| C1 | 1µF | 50V | 1x |
| C7 | 1µF | 50V | 1x |
| C9 | 1µF | 50V | 1x |
| C15 | 47µF | 16V | 1x |
| C21 | 1µF | 50V | 1x |
| C24 | 220µF | 10V | 1x |
| C27 | 1µF | 50V | 1x |
| C31 | 1µF | 50V | 1x |
| C32 | 1µF | 50V | 1x |
| C33 | 1µF | 50V | 1x |
| C34 | 1µF | 50V | 1x |
> Note: Capacitor numbering may vary slightly between early 128K and 512K revisions. Always verify location and values against your specific board version before ordering replacements.
Capacitor Replacement Procedure
[edit | edit source]Proper capacitor replacement requires care and the right tools. Follow these steps:
- Discharge CRT – Fully discharge the CRT before opening the system to avoid electric shock.
- Disassembly – Carefully remove the analog board and/or logic board, noting cable connections.
- Desoldering – Use a solder pump or wick to remove capacitors without lifting traces.
- Install Replacements – Insert new capacitors with correct polarity (+ and – markings).
- Soldering – Apply clean, shiny joints and trim excess leads.
- Final Inspection – Confirm all joints are clean and test for shorts using a multimeter.
Recommended Tools
[edit | edit source]- Temperature-controlled soldering iron (fine tip)
- Desoldering braid or solder sucker
- Multimeter (continuity and voltage testing)
- Isopropyl alcohol and ESD brush (for board cleaning)
- Safety glasses and insulated gloves
Voltage Adjustment Post-Recap
[edit | edit source]After recapping, test voltages at the floppy or logic board connector using a multimeter:
- +5V Rail: 4.85V – 5.15V
- +12V Rail: 11.9V – 12.7V
Adjust if necessary using the analog board’s trimmer potentiometer (R56).
Additional Tips
[edit | edit source]- Power up the Macintosh periodically to preserve capacitor function.
- Always use high-quality capacitors from trusted brands.
- If full recapping isn't feasible, replace in matching sets or sections.
- Recycle old capacitors at an electronics waste facility.