Power Macintosh 8100 Capacitor Replacement Guide

Power Macintosh 8100 logic board with the 13 surface-mount 47 µF 16 V electrolytics circled. Photo: Qrani; annotation: MacDat

The Power Macintosh 8100 has two sets of electrolytic capacitors that age: thirteen 47 µF surface-mount electrolytics on the logic board, and the through-hole capacitors in the power supply, for which an owner's list exists for the Delta-built version. MacDat's capacitor reference counts 13 × 47 µF 16 V surface-mount electrolytics on the logic board. Apple's schematic for the 8100/110 logic board shows the same thirteen 47 µF parts and gives their designators, along with 25 smaller polarised capacitors.

Apple's Service Source treats the logic board and power supply as single parts (logic boards 661-0199, 661-0209 and 661-1026; supplies 661-0232 and 661-1687) and gives no component values.

Logic board capacitors

47 µF capacitors on the 8100 logic board (Apple's 8100/110 schematic)

Position	Value	Voltage printed	Rail or function on the schematic	Sheet
C17	47 µF	none printed	+5 V audio supply (output of the 78M05 regulator VR1)	19
C29	47 µF	none printed	Speaker amplifier supply	19
C31	47 µF	none printed	Audio output common coupling	19
C43	47 µF	none printed	Audio output left coupling	19
C59	47 µF	none printed	Audio output right coupling	19
C60	47 µF (faint)	illegible	Bulk supply capacitor	16
C62	47 µF	16 V	Processor core supply (output of the LT1085 regulator VR3)	3
C63	47 µF	16 V	Processor core supply (VR3 output)	3
C67	47 µF	16 V	Trickle 5 V	16
C75	47 µF	16 V	+12 V	16
C76	47 µF	16 V	−12 V; positive end to ground	16
C77	47 µF	16 V	−5 V (output of the 79M05 regulator VR4); positive end to ground	16
C105	47 µF	16 V	Cuda supply	16

MacDat gives all thirteen as 47 µF 16 V surface-mount electrolytics. The value of C60 is faint on the scanned schematic.

Smaller polarised capacitors on the 8100/110 schematic

Value	Positions	Notes
10 µF 16 V	C61, C78, C361	Processor regulator input and output (sheet 3); clock supply (sheet 11)
10 µF 16 V tantalum	C288, C362	Clock supply filters (sheet 11)
10 µF	C45, C48, C49, C89	Curio analogue supply and SCSI terminator power (sheets 13, 14); no voltage printed, C45 poorly printed
10 µF	C96, C90	Cuda synthesiser supply (sheet 16); floppy controller supply (sheet 20); no voltage printed
10 µF	C10, C16, C18, C19	Audio: regulator input and telecom audio output coupling (sheet 19); no voltage printed
1 µF	C23, C24, C25, C35, C36, C39, C40, C47, C53, C54	Audio input coupling and speaker volume (sheet 19); no voltage printed

These 25 parts are polarised on the schematic, but apart from C288 and C362, which are marked tantalum, it does not say whether they are tantalum or electrolytic, and MacDat does not list them. Check each one on the board before ordering.

The schematic is for the 8100/110 board; MacDat's photograph is of a board marked 8100/80. The two agree on thirteen 47 µF parts, but MacDat's photograph does not show designators.

Power supply capacitors

Apple's service parts for the 8100 supply are 661-1687 and 661-0232. Apple's Module Identification manual gives 661-1687 as its 200 W supply, with assembly number 614-0012 on the module label; that number identifies Apple's part, not the maker. Apple Rescue of Denver lists the 8100 supply under all three numbers and says it was made by several manufacturers, including Delta and Magnetek. The list below is for the Delta SMP-220DB only, so read the maker's name and model on the supply's own label before ordering parts.

An owner who refurbished a Delta SMP-220DB published this list. The supply comes apart into five boards, four of which carry electrolytics. All are 105 °C parts except C1 and C2, which are 85 °C.

Delta SMP-220DB electrolytic capacitors, from an owner's list

Board	Position	Value	Voltage	Size (length × diameter, mm)
SMP-220DP-1 (main board)	C104, C105	3300 µF	10 V	36 × 13
	C106	2200 µF	10 V	28 × 13
	C107	1000 µF	10 V	20 × 10
	C154, C156	1000 µF	16 V	28 × 10
	C252, C807	470 µF	35 V	20 × 10
	C253	220 µF	16 V	15 × 18
	C513	10 µF	50 V	11 × 5
SMP-220DP (primary board)	C1, C2	820 µF	200 V	40 × 30
	C301	470 µF	35 V	20 × 10
	C302	0.47 µF	50 V	11 × 5
	C304	4.7 µF	50 V	11 × 5
	C952	1 µF	50 V	11 × 5
DC-267	C507	2.2 µF	50 V	11 × 5
	C511	22 µF	50 V	11 × 5
	C532, C601	10 µF	50 V	11 × 5
	C655, C674	4.7 µF	50 V	11 × 5
	C783	1 µF	50 V	11 × 5
	C784	100 µF	25 V	11 × 7
DC-230 (smallest board)	C804	2.2 µF	50 V	11 × 5

The list's first version gave C253 as 22 µF; its author corrected it to 220 µF. C1 and C2 are the primary reservoir capacitors and charge from the mains. Replacing every capacitor did not revive that owner's supply, which kept clicking on and off. Another owner's dead supply needed its LM339N comparator and two 180 Ω resistors (R955A, R955B) replaced; see Power Macintosh 8100 Troubleshooting.

Inspection

Check the supply first. Apple's chart for a machine that does not power up resets the logic board, reseats the ROM and cache SIMMs, and then replaces the power supply before the logic board (SS p. 40); the connector voltages are on Power Macintosh 8100 Troubleshooting. Take out the logic board as described on Power Macintosh 8100 General Maintenance. Look for:

• electrolyte residue, discoloured pads or corrosion round the 47 µF parts
• bulging or leaking cans
• corrosion near the clock 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.

Replacement

1. Photograph the board and record every value, voltage and polarity before removing anything.
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, observing polarity. C76 and C77 sit on negative rails with their positive ends to ground. On an aluminium electrolytic the marked side is negative; on a tantalum the stripe marks the positive end.
4. Do not unplug or disturb the thermoelectric cooler wires on 8100/100 and 8100/110 boards; Apple warns that unplugging them can damage the board.
5. Check each new part for a short to ground before the first power-up.

For the Delta supply, discharge C1 and C2 and confirm with a meter before touching the primary board, record the orientation of every part, and, as one owner did, test the repaired supply through a lamp in series or from a current-limited supply before connecting it to the logic board.

Related pages

• Power Macintosh 8100
• Power Macintosh 8100 General Maintenance
• Power Macintosh 8100 Troubleshooting
• Capacitor Failure Symptoms
• Recommended Tools