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Power Macintosh 9600 Capacitor Replacement Guide

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Power Macintosh 9600 logic board 820-0865-A. Photo: Gona.eu, Wikimedia Commons, CC BY-SA 3.0

No community capacitor list has been published for the Power Macintosh 9600 or 8600 logic boards. Apple's schematic for the first 9600 board, 820-0865-A, is hosted here, and the table below lists every polarised capacitor drawn on it: 46 fitted positions and three marked "NO STUFF" (not fitted).[1] The schematic does not say whether each part is an aluminium electrolytic or a tantalum. MacDat lists the capacitors on the 8500 board as surface-mount electrolytics.[2]

The table applies to board 820-0865-A, used in the 9600/200, 9600/200MP and 9600/233. The later board for the 300 and 350 MHz models and both 8600 boards differ.[3] Apple's Service Source shows the 8600/250 and 8600/300 board without the cache slot of the 8600/200.[4] The service manual gives no component values.

Logic board capacitors (820-0865-A)

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Polarised capacitors on Apple's 9600 schematic
Positions Value Voltage Rail on the schematic Sheet
C1, C2 47 µF 16 V +5 V at the processor card connector 2
C3, C4 47 µF 16 V +3.3 V at the processor card connector 2
C68, C69 47 µF 16 V +5 V at the memory slots 8
C70, C71 47 µF 16 V +5 V at the memory slots 9
C72, C73 47 µF 16 V +5 V at the memory slots (sheet titled "additional RAM SIMMs for Tsunami") 10
C338 47 µF 16 V +3.3 V at PCI slots A–C 13
C337 47 µF 16 V +3.3 V at PCI slots D–F 14
C151 47 µF 16 V +5 V to the AAUI Ethernet connector, through fuse F1 (1.5 A) 16
C132 10 µF 16 V Analogue supply on the Ethernet sheet 16
C52 10 µF 16 V −5 V (output of the 79L05 regulator); positive end to ground 17
C183, C185 10 µF 16 V External SCSI terminator power, regulator input and output 18
C194, C197 10 µF 16 V Internal Fast SCSI terminator power, regulator input and output 19
C204, C205, C206, C207, C208, C209, C211, C212 47 µF 16 V +5 V bulk 20
C236 47 µF 16 V +5 V at the power connector J36 20
C231 47 µF 16 V +12 V, after fuse F4 20
C235 47 µF 16 V −12 V; positive end to ground 20
C232 47 µF 16 V Trickle 5 V, near connector J39 20
C226 47 µF 16 V Cuda supply 20
C254, C255 10 µF 16 V Audio 12 V and the 5 V regulator output feeding the AWACS chip 22
C271 47 µF 16 V Speaker amplifier 12 V supply 22
C265, C266, C268 100 µF 6.3 V Line output coupling (left, right, common) 22
C246, C247, C248, C249, C250, C253 1 µF 10 V CD and microphone/line input coupling 22
C263, C264 0.47 µF 25 V AWACS reference bypass 22
C353, C354, C355 1 µF 10 V Marked NO STUFF (not fitted) 22

Totals: 27 × 47 µF 16 V, 8 × 10 µF 16 V, 3 × 100 µF 6.3 V, 6 × 1 µF 10 V and 2 × 0.47 µF 25 V fitted. Sheets 3–7, 11, 12, 15, 21 and 23–26 carry no polarised capacitors.[1] The scanned schematic has handwritten value changes on sheet 22, all to small ceramic capacitors, none to the parts above.[1]

Inspection

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Swing out the top chassis to reach the board, or remove it as described on Power Macintosh 9600 General Maintenance. Look for:

  • electrolyte residue, dark rings or corrosion round the capacitor pads, especially the bulk group on the +5 V rail and the parts beside the memory slots
  • bulging or leaking cans
  • corrosion near the battery holder; a leaking lithium cell leaves acidic residue (see Battery Explosion, Capacitor or Corrosion Damage)

Capacitor Failure Symptoms describes what failing parts look like. An 8600 owner reports recapping 8600 boards with tantalum capacitors before the originals leaked.[3]

Replacement

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  1. Photograph the board and record the value, voltage and polarity of every part before removing anything; compare what is fitted with the table, because boards differ.
  2. Remove each capacitor with hot air or two irons without lifting the pads, and clean away electrolyte with isopropyl alcohol.
  3. Fit parts of the same capacitance and at least the same voltage rating. C52 and C235 sit on negative rails with their positive ends to ground.[1] On an aluminium electrolytic the marked side is negative; on a tantalum the stripe marks the positive end.
  4. Leave the NO STUFF positions empty.
  5. Check each new part for a short to ground before the first power-up.

Power supply

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No capacitor list has been published for the 8600 and 9600 supply, Apple service part 661-1242.[4] Owners' reports of failures in its standby circuit and in a power-control IC are on Power Macintosh 9600 Troubleshooting. The primary side holds about 300 V DC from the mains; discharge it and confirm with a meter before working on it.[5]

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References

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  1. ↑ 1.0 1.1 1.2 1.3 Apple Computer, SCHEM, PCB, MN LG BD, 9600 (PCB 820-0865-A), sheets 2–26, read sheet by sheet; polarised capacitors are drawn with a "+" mark and a curved plate. Hosted as File:Power Macintosh 9600 logic board schematic (820-0865-A).pdf; see Power Macintosh 9600 Logic Board Schematic.
  2. ↑ MacDat, "Power Macintosh 8500 Capacitor Reference": ten 47 µF 16 V, seven 10 µF 16 V and five 4.7 µF 25 V, all surface-mount electrolytic.
  3. ↑ 3.0 3.1 68k Macintosh Liberation Army forum, "PowerMac 9600 Logic Boards" (2022), post by aplmak: recapped 8600 boards (820-0858-B and 820-0931-A) with tantalum capacitors as a precaution.
  4. ↑ 4.0 4.1 Apple Computer, Service Source: Power Macintosh 8600/9600 & WS 9650 (1997), PDF pp. 40–42 (logic board diagrams); exploded views pp. 234–235 (logic boards 661-0394 and 661-1221 for the 9600, 661-0387 and 661-1220 for the 8600; power supply 661-1242). File:Pm8600.9600.ws9650.pdf; see Power Macintosh 8600/ 9600 & WS 9650 Service Source.
  5. ↑ 68k Macintosh Liberation Army forum, "9600 power supply failure modes/schematic?" (2022): roughly 300 V DC on the primary side of a 9600 supply.
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