Macintosh Centris 650 Capacitor Replacement Guide

This guide covers capacitor diagnosis and replacement on the Macintosh Centris 650 and the Macintosh Quadra 650. The two machines share one logic board design and one power supply; Apple documents them together in a single service manual.

Safety

The power supply is a mains-rectified switching supply. Its primary side sits at mains potential and the two large reservoir capacitors hold a charge that can kill after the machine is unplugged. Recapping it is a perfectly reasonable job, but treat it as live-mains work:

1. Switch off and unplug the mains lead.
2. Discharge each large reservoir capacitor through a 1 kΩ / 5 W resistor across its terminals, then confirm with a meter that it reads near zero before touching anything.
3. Work one-handed where practical, and do not probe a powered primary side without an isolation transformer.

There is no CRT in the system unit. The matching Apple displays contain their own tube and supply and are serviced separately — see CRT Discharge Procedure if you are working on a monitor.

The supply is self-configuring for 100–240 V AC at 50–60 Hz, so there is no voltage selector to set wrongly. Apple rates the machine at 112 W maximum, not including display power.

What Actually Fails

• The logic board does not carry surface-mount aluminium electrolytic capacitors. Two independent 68kMLA members who have had Centris 650 boards in front of them report that the board is populated with tantalum and ceramic parts: "All the other caps on the Centris PCBs are tantalum or ceramic", and "The 650 has solid state caps on the logic board already." That means the corrosion damage seen on the Macintosh Centris 660AV, Macintosh Quadra 840AV and the compact Macs does not apply here. This is a community finding, not an Apple statement — check your own board before you take anyone's word for it.
• Tantalums fail short, not open. A shorted decoupling tantalum pulls its rail down and the supply either shuts down or blows a fuse. Look for a cracked or blackened moulded block rather than for weeping electrolyte.
• The power supply does carry aluminium electrolytics, and it is the part of this machine that realistically needs recapping.

Apple published no capacitor values for this machine. The Service Source contains no capacitance, working-voltage or component-designator data anywhere — not in Specifications, not in Troubleshooting, not in Take Apart. Apple serviced these at module level: every power fault in the symptom charts ends in "Replace power supply." Any table of "Centris 650 capacitor values" is therefore somebody's reading of a particular board, not a manufacturer specification.

Identifying the Power Supply

The Centris 650 uses the same physical supply as the IIcx, IIci, IIvi, IIvx, Performa 600 and Quadra 700, but at a higher rating. Apple part numbers and their manufacturers, taken from the labels on the units themselves:

Apple P/N	Fitted to	Manufacturer and model	Rated output
699-0392	IIci	Astec AA15830	+5 V 12 A • +12 V 1.5 A • −12 V 1.0 A • +5 V 1 mA continuous
614-0004	IIci, Quadra 700	Astec AA15831 • GE 9T89Y5005G11	+5 V 12 A • +12 V 1.5 A • −12 V 1.0 A • +5 V 1 mA continuous
614-0009	Centris 650, Power Macintosh 7100	Astec AA16870 • Delta SMP-120EB	+5 V 15 A • +12 V 2.5 A • −12 V 0.6 A • +5 V 1 mA continuous

The "+5 V 1 mA continuous" line is the trickle rail that keeps the soft-power circuit alive. If a machine is completely dead, measuring that rail is the first useful go/no-go check: present means the primary side is running and the fault is downstream; absent means the fault is in the mains input, the primary switcher or the standby circuit.

Note the Centris 650's supply is the higher-rated 614-0009 unit. It is mechanically interchangeable with the earlier ones, so a supply swapped in from a IIci will fit but will give less headroom on +5 V and +12 V.

Power Supply Capacitors

The list below is one member's board-by-board reading of a Centris 650 supply, with the board silkscreen markings he recorded. Where the designator was obscured by the factory adhesive he noted the nearest legible part instead; those rows are marked "near". It is a secondary source and covers one physical unit — read the markings on your own supply before ordering.

Board	Designator	Value	Notes
SMP-120 EP	C1, C2	470 µF 200 V	Bulk reservoir pair, radial
SMP-120 EP	C807	470 µF 35 V
SMP-120 EP-1	C103	2200 µF 10 V
SMP-120 EP-1	C551	1000 µF 35 V
SMP-120 EP-1	C252	470 µF 25 V
SMP-120 EP-1	near C105 / C155 / C253	1000 µF 16 V	Designators obscured by adhesive
SMP-120 EP-1	near D255	470 µF 16 V	Designator obscured by adhesive
SMP-120 EP-1	C302 and neighbour, C612, C684	10 µF 50 V
SMP-120 EP-1	C505	2.2 µF 50 V

The 200 V reservoir pair

C1 and C2 are in series across the rectified mains, which is how the supply manages 100–240 V input on 200 V parts. On 230–240 V mains the rectified DC bus sits at roughly 340 V, and only the series pair holds it off; 200 V across each is correct, and the two together give 400 V of margin.

Consequently:

• Never fit a single capacitor in place of the pair. A lone 200 V part in that position will fail on European mains, violently.
• Replace both at once with matched parts of the same value and voltage, or higher.
• Do not "improve" the design by fitting one 400 V part across both positions unless you also understand what the balancing resistors are doing.

Logic Board Capacitors

There is nothing to do here as routine maintenance. If a tantalum has failed:

1. Identify it — look for a cracked, split or scorched moulded block, and for a rail that measures as a short to ground with the supply disconnected.
2. Note the orientation. Tantalums are polarised and the bar marks the positive end, which is the opposite convention to an aluminium electrolytic's stripe.
3. Remove with hot air or by alternating a fine iron between the two terminations.
4. Fit a replacement of the same capacitance with generous voltage derating. Solid tantalums should be derated by about 50 %: a part on a 5 V rail wants a 10 V or higher rating, and a part on 12 V wants 25 V.
5. Polymer aluminium or polymer tantalum parts are a reasonable substitute and fail benignly rather than shorting.

For what failing capacitors look like in general, see Capacitor Failure Symptoms.

Replacement Procedure

1. Discharge the supply as described above and confirm with a meter.
2. Photograph each board before removing anything. The supply comes apart into stacked sub-boards and they only go back one way.
3. Desolder with a temperature-controlled iron and a pump or wick. The bulk capacitors sit on heavy ground pours and need more heat and dwell than the small parts.
4. Clean the pads with isopropyl alcohol.
5. Fit the replacements the right way round — on aluminium electrolytics the stripe marks the negative lead.
6. Trim the leads flush and check for bridges and stray clippings before reassembly.
7. Reassemble, then bring the supply up on a dummy load — a car headlamp bulb across +5 V and another across +12 V works — before connecting it to the logic board.

Use 105 °C, low-ESR parts rated for switching-supply ripple. See Recommended Tools for the soldering and cleaning kit this wiki recommends.

Battery

Apple's documented check: set a voltmeter to the 10 V DC range, measure across the cell in its holder, and replace it if it reads below 3.2 V. The cell sits in a holder with a latched cover — prise the latch open with a small flat-blade screwdriver, lift the cover off and lift the cell out. It is not soldered in.

A leaking cell will corrode the traces underneath it long before it stops holding a date. Check it whenever the machine is open. If it has already leaked, see Battery Explosion, Capacitor or Corrosion Damage.

What the Symptom Charts Actually Say

Apple's own troubleshooting for this machine ends in "Replace power supply" for the following, which is the best available guide to when the supply rather than the logic board is at fault:

• No power at all, fan not turning, no start-up chime.
• The machine powers on but shuts down intermittently.
• The fan and drives run but there is no video and no chime.
• Drives that will not spin up while the rest of the machine runs.

Before condemning the supply, check the battery — Apple lists a battery check among the steps for start-up failures, because a flat or leaking cell can stop the soft-power circuit latching.

Related Pages

• Macintosh Centris 650
• Macintosh Centris 650 Troubleshooting
• Macintosh Centris 650 General Maintenance
• Macintosh Quadra 650
• Capacitor Failure Symptoms
• Recommended Tools