Macintosh Centris 650 Capacitor Replacement Guide

Macintosh Centris 650 (photo: Benoît Prieur, CC0)

Capacitor diagnosis and replacement for the Macintosh Centris 650 and the Macintosh Quadra 650, which Apple services together in one Service Source volume. On this machine the logic board is not the recap job; the power supply is.

Safety

The power supply is a mains-rectified switching supply. Its primary side is at mains potential and the two large reservoir capacitors hold a lethal charge after the machine is unplugged.

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. Do not probe a powered primary side without an isolation transformer.

The system unit has no CRT. Apple's displays contain their own tube and supply; see CRT Discharge Procedure when working on one.

The supply accepts 100–240 V AC at 50–60 Hz with no voltage selector, and Apple rates the machine at 112 W maximum, not including display power.

What fails

• The logic board has no surface-mount aluminium electrolytics. Retro Viator found none on a Quadra 650 logic board, only tantalums, while the supply did contain electrolytics and had a patch scorched by a hot resistor. A TinkerDifferent member says the Centris 650, Quadra 650 and Quadra 800 boards all came with tantalums from the factory. Check your own board.
• Solid tantalums most often fail short. A shorted filter tantalum pulls its rail down, and the supply shuts down or its fuse blows. Look for a cracked or scorched moulded body.
• The power supply does use aluminium electrolytics.

Apple published no capacitor values for this machine. The Service Source has no capacitance, voltage-rating or designator data; power faults in its symptom charts end at "Replace power supply".

Identifying the power supply

Apple's service part number for the supply is 661-0758. Apple's developer note says it is the same physical size as the Quadra 700's supply but delivers up to 112 W. Apple Rescue of Denver lists the same supply as Apple 614-0009 (service part 661-0758), 112 W, made by Delta (SMP-120EB) or ASTEC (AA16870), and fitted to the Centris and Quadra 650, IIvi, IIvx, Performa 600 and Power Macintosh 7100. Two makers means two different capacitor lists: open the supply and read the maker and board markings before ordering.

Power supply capacitors

Console5's community list, read from a Delta SMP-120EB supply, has fifteen electrolytics. It has no list for the ASTEC AA16870 version; read the markings on that one.

Delta SMP-120EB electrolytics (Console5)

Designator	Value
C1, C2	470 µF 200 V (680 µF on some revisions)
C103	2200 µF 10 V
C104, C153, C154	1000 µF 16 V
C252	470 µF 25 V
C253	470 µF 16 V
C302, C522, C612, C684	10 µF 50 V
C505	2.2 µF 50 V
C551	1000 µF 35 V
C807	470 µF 35 V

The 200 V reservoir pair

C1 and C2 are 200 V parts on a supply that accepts 240 V mains, which rectifies to about 340 V DC; a single 200 V capacitor cannot hold that, so the two work as a series pair across the rectified bus. Replace both together with matching parts of the same value and at least the same voltage rating, and never fit a single 200 V capacitor in place of the pair.

Logic board capacitors

There is no routine work to do here. If a tantalum has failed:

1. Find it: look for a cracked, split or scorched body, and for a rail that measures as a short to ground with the supply disconnected.
2. Note its orientation. The bar on a tantalum marks the positive end, the opposite of an aluminium electrolytic's stripe.
3. Remove it with hot air, or by alternating a fine iron between the two terminations.
4. Fit a replacement of the same capacitance, derated by 50 %: a part on the 5 V rail wants a 10 V or higher rating, and one on 12 V wants 25 V. Some restorers use solid polymer electrolytics instead.

For the signs of failure in general see Capacitor Failure Symptoms.

Replacement procedure

1. Discharge the supply as above and confirm with a meter.
2. Photograph each board before removing anything. The supply is built from stacked sub-boards.
3. Desolder with a temperature-controlled iron and a pump or wick. The reservoir capacitors sit on heavy copper and need more heat.
4. Clean the pads with isopropyl alcohol.
5. Fit the replacements the right way round; the stripe on an aluminium electrolytic marks the negative lead.
6. Trim leads, then check for bridges and stray clippings.
7. Test the supply on a dummy load before connecting it to the logic board.

Use 105 °C, low-ESR parts suited to switching supplies. See Recommended Tools.

Battery

Apple's check: set a voltmeter to the 10 V DC range, measure the battery in its holder (positive end marked "+" on the logic board), and replace it if it reads below 3.2 V. The holder has a latched cover; prise the latch with a small flat-blade screwdriver and lift the battery out. If it has leaked, see Battery Explosion, Capacitor or Corrosion Damage.

Apple's symptom charts and the power supply

Apple's charts include "Replace power supply" among the cures for:

• no power, black screen, fan not running and LED off;
• clicking, chirping or thumping (power supply first, then logic board);
• intermittent shutdown, after checking the air vents (thermal protection can shut the machine down for 30 to 40 minutes), the power cord and the battery;
• intermittent crashes or lock-ups, after software, SCSI and SIMM checks;
• a dark screen with no sound and no drive activity while the fan runs and the LED is lit, after removing peripherals and NuBus cards and trying DRAM and VRAM;
• no CD-ROM icon on the desktop.

Related pages

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