Power Macintosh 7100 Capacitor Replacement Guide

The Power Macintosh 7100 logic board, 820-0597-A, uses surface-mount tantalum capacitors. Console5 lists 26 of them: twenty-five 47 µF 16 V parts and one 100 µF 6.3 V part, and sells them as a "tantalum main PCB cap kit". Apple's Power Macintosh 7100 Series Service Source is module-level and names no capacitors; it treats the power supply as one part, 661-0758, and the logic board as 661-0897 or 661-0208.

Apple's 7100 logic board connector diagram (Service Source p. 18). It shows connectors and slots, not capacitor positions

Logic board capacitors

Power Macintosh 7100 logic board (820-0597-A), from Console5

Position	Value	Rating
C13	47 µF	16 V
C15	47 µF	16 V
C18	47 µF	16 V
C19	47 µF	16 V
C22	47 µF	16 V
C25	47 µF	16 V
C26	47 µF	16 V
C29	47 µF	16 V
C30	47 µF	16 V
C31	47 µF	16 V
C33	47 µF	16 V
C34	47 µF	16 V
C35	47 µF	16 V
C38	47 µF	16 V
C40	47 µF	16 V
C42	47 µF	16 V
C43	47 µF	16 V
C44	47 µF	16 V
C45	47 µF	16 V
C46	47 µF	16 V
C53	47 µF	16 V
C56	47 µF	16 V
C58	47 µF	16 V
C62	100 µF	6.3 V
C63	47 µF	16 V
C65	47 µF	16 V

Source: Console5. This is a community list, not an Apple one; read the marking on each part before removing it and go by what is on the board.

Do they need replacing?

Apple's 7100 symptom charts do not mention capacitor faults. Recap-a-Mac's verdict on the related Power Macintosh 6100 board, which uses the same 47 µF 16 V tantalums, was that it "probably" does not need recapping yet. Replace a part when it is visibly damaged, shorted or out of value, or when there is corrosion round it. The Recap-a-Mac finding is for the 6100 board, not the 7100.

Inspection

Remove the top housing, power supply, drive chassis, video card and reset/interrupt actuator, take out the SIMMs, cache and ROM, and lift out the logic board as Apple describes (pp. 53–88). The procedure is summarised on Power Macintosh 7100 General Maintenance. Look for:

• cracked, scorched or discoloured tantalum bodies
• corrosion or residue round the battery holder; a leaking lithium cell leaves acidic residue (see Battery Explosion, Capacitor or Corrosion Damage)
• corrosion on the SIMM, ROM and cache sockets

Capacitor Failure Symptoms describes what failing parts look like.

Replacement

1. Photograph the board and note the value, voltage and polarity of each part before removing anything.
2. Remove the tantalum with hot air or two irons without lifting the pads.
3. Fit the new part the right way round. On a tantalum capacitor the band marks the positive terminal, the opposite of the band on an aluminium electrolytic.
4. Use a replacement of the same capacitance and at least the same voltage rating. If you fit aluminium electrolytics in place of tantalums, their band marks the negative lead.
5. Clean off flux with isopropyl alcohol and check for bridges.
6. Before the first power-up, measure across each new part for a short to ground.
7. Refit the logic board, ROM, cache and SIMMs (the ROM and cache sockets are interchangeable; check which module goes where), video card, drive chassis and power supply, then reset the logic board as Apple describes (pp. 86, 124–128).

Power supply

Neither Apple's manual nor Console5 lists the capacitors of the 661-0758 supply. Record the values from the board before removing anything and fit parts of the same capacitance and at least the same voltage rating. The supply is auto-ranging for 100–240 V (p. 31), so the primary-side reservoir charges to about 340 V on 240 V mains (240 × √2). Discharge it and confirm with a meter before touching the primary side.

Related pages

• Power Macintosh 7100
• Power Macintosh 7100 General Maintenance
• Power Macintosh 7100 Troubleshooting
• Power Macintosh 6100 Capacitor Replacement Guide
• Capacitor Failure Symptoms