RetroTechCollection

Power Macintosh G3 (Beige) Capacitor Replacement Guide

Capacitor list and replacement notes for the logic board (820-0991), personality card and voltage regulator card of the Power Macintosh G3 (Beige). The same board is used in the desktop, the minitower and the Power Macintosh G3 All-in-One, so the logic board list applies to all three.[1][2] Apple's Service Source gives no capacitor data; the values here come from Console5's list, an owner's recap and Apple's pre-production schematic.

Apple's diagram of the logic board; the voltage regulator card plugs in at lower left (Service Source, PDF p. 85)

Do they need replacing?

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The board uses surface-mount aluminium electrolytics. One owner found some leakage under a few of them on a minitower that had stopped starting; another 68kMLA member reports the capacitors on his beige G3s are still good, sees no need to recap them preventively, and recapped one dead board without curing it.[1] Check for leakage, residue and a fishy smell before deciding; see Capacitor Failure Symptoms. For damage from a leaking PRAM battery, see Battery Explosion, Capacitor or Corrosion Damage.

Logic board

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Logic board 820-0991-A and -B[3]
Designator Value Voltage
C5 47 µF 16 V
C6 100 µF 6.3 V
C7 47 µF 16 V
C17 100 µF 6.3 V
C49 100 µF 6.3 V
C74 100 µF 6.3 V
C76 47 µF 16 V
C78 47 µF 16 V
C110 47 µF 16 V
C176 47 µF 16 V
C248 47 µF 16 V
C250 47 µF 16 V
C251 47 µF 16 V
C255 47 µF 16 V
C259 47 µF 16 V
C261 47 µF 16 V
C306 (designator unconfirmed) 10 µF 16 V
C328 47 µF 16 V
C336 47 µF 16 V
C369 47 µF 16 V
C370 47 µF 16 V

That is 16 × 47 µF 16 V, 4 × 100 µF 6.3 V and 1 × 10 µF 16 V, which matches the owner's count once the 100 µF part on the personality card is taken out.[3][1]

Apple's DVT schematic (a pre-production revision dated 20 May 1997) gives the same values for C7 (47 µF 16 V), C74 (100 µF 6.3 V), C76 and C78 (47 µF 16 V) on sheet 3, the processor voltage regulator connector sheet. The same sheet shows C96 (330 µF 6 V) and C106 (100 µF 10 V) marked "no stuff", and sheet 17 shows two small polarised parts, C227 (2.2 µF 35 V) and C228 (4.7 µF 10 V), that neither list includes. Check those positions on your own board before ordering.[4]

Personality card

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One 100 µF 6.3 V capacitor, found by the owner on both the audio-only and the video in/out card he recapped. Check your own card.[1]

Voltage regulator card

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The processor regulator is a separate plug-in card (Apple service part 922-3292) with four tall through-hole electrolytics.[5][1] Several makers built these cards, and two values have been reported:

Card Capacitors Source
Card in an -A revision desktop; card in an owner's minitower 4 × 1500 µF 6.3 V Console5; shadedream[3][1]
Card in a -B revision server (Console5); card labelled Switch Power, Apple P/N 614-0081 4 × 680 µF 10 V (C6-C9 on Console5's list) Console5; croissantking[3][1]

Read the values off your own card. The originals on one card were low-impedance Nichicon UPW parts; use low-impedance electrolytics or solid polymer capacitors of the same value and at least the same voltage. One owner found the legs soldered into large ground planes on both sides and used hot air to remove and refit them.[1]

Replacement

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  1. Remove the logic board as described on Power Macintosh G3 (Beige) General Maintenance#Removing the logic board: open the case, take out the cards and processor module, unplug the cables, take out the column support screw and the processor wire screw, and slide the board forward off its tabs.[5]
  2. Pull the voltage regulator card and the personality card and work on them separately.
  3. Remove the PRAM battery before working on the board.
  4. Replace the surface-mount parts one at a time, matching polarity. The 10 µF part is very small; one owner suggests a slightly larger replacement to make soldering easier.[1] Owners on the same thread advise polymer over tantalum for the surface-mount positions.[1]
  5. Refit the board. When refitting the processor module wire, use a hand screwdriver: Apple warns of a capacitor right beside the screw hole.[5]
  6. Check J28 and J16 before powering up.[5]

No capacitor list has been found for the desktop or minitower power supplies.

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References

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  1. ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 68kMLA forum thread "Beige PowerMac G3 Capacitor Replacement", August 2023 to August 2024. shadedream (minitower): 16 × 47 µF 16 V, 5 × 100 µF 6.3 V (one on the personality card, on both his basic and video in/out cards) and 1 × 10 µF 16 V; regulator board 4 × 1500 µF 6.3 V through-hole, low-impedance Nichicon UPW on his; replaced the SMD parts with tantalums and the regulator caps with solid polymers; the 10 µF part is very small; regulator cap legs are tied to large ground planes on both sides and he used hot air to remove and refit them; some leaking under a few caps; the old regulator caps showed no leakage. 3lectr1cPPC: the tower, desktop and AIO boards are the same. Phipli: his beige G3s' caps are still good and there is no real need to recap preventively; these fail by stopping working, not by corroding the board. croissantking: suggests low-impedance electrolytics for the regulator; his regulator labelled Switch Power, Apple P/N 614-0081, has 4 × 680 µF 10 V. mmic1101y: was cautioned against tantalum and will use polymer. Community repair report.
  2. ↑ 68kMLA forum thread "G3 AIO Power Supply Jumper", September 2012. mcdermd: his beige G3 desktop board is the same part, 820-0991-A, as the one in his All-in-One. Community experience.
  3. ↑ 3.0 3.1 3.2 3.3 Console5 Tech Wiki, "Macintosh G3" (retrieved 2026-10-02, via the wiki's raw page). "Confirmed for 820-0991-A / 820-0991-B"; C306 marked with a question mark; switch board in the -A revision G3 desktop 4 × 1500 µF 6.3 V; switch board in the -B revision G3 server C6-C9 680 µF 10 V. Secondary source.
  4. ↑ Apple Computer, Power Macintosh Gossamer - DVT main logic board schematic, Rev 5, last changed 20 May 1997, hosted here as File:Power Macintosh G3 Gossamer logic board schematic (DVT, 1997).pdf (see Power Macintosh G3 Documentation). Sheet 3 (microprocessor VRM connector and pull-ups): C7 47 µF 16 V, C74 100 µF 6.3 V, C76 and C78 47 µF 16 V; C96 330 µF 6 V and C106 100 µF 10 V marked NO STUFF. Sheet 17 (SCSI and floppy): C227 2.2 µF 35 V and C228 4.7 µF 10 V polarised; F2 0.9 A fuse. Pre-production drawing.
  5. ↑ 5.0 5.1 5.2 5.3 Apple Computer, Power Macintosh G3 Desktop Service Source, hosted here as File:Power Macintosh G3 Desktop and Minitower Service Source.pdf (see Power Macintosh G3 Desktop and Minitower Service Source). PDF page numbers: voltage regulator Hot Issue p. 7 and theory p. 219; Open Internal Chassis pp. 139-142; Processor Module pp. 161-170 (capacitor beside the processor wire screw, p. 162); Logic Board pp. 190-196; Exploded View p. 256 (voltage regulator card 922-3292).


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