Macintosh Quadra 800 Capacitor Replacement Guide

Macintosh Quadra 800

This guide covers capacitor diagnosis and replacement on the Macintosh Quadra 800 and the Workgroup Server 80, which share one logic board, one enclosure and one power supply.

On this machine the work is in the power supply. The logic board is a different design from the leaking surface-mount boards of the same period.

Safety

The supply is a mains-rectified switcher. Its primary side sits at mains potential and the two 200 V bulk capacitors hold a charge that can kill after the machine is unplugged. Recapping it is a reasonable job, but treat it as live-mains work:

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

This supply comes apart into five stacked boards, which means components on the primary side end up exposed and easy to reach across. One member who reassembled it with a joint left unsoldered had the mains-side safety capacitors detonate when he plugged it in — nothing caught fire, but it was loud and it could have been much worse. Reflow every joint you disturbed before the unit sees mains again.

There is no CRT in the system unit — see CRT Discharge Procedure only if you are working on a monitor.

What Actually Fails

• The logic board is reported to carry solid (tantalum) capacitors, not surface-mount aluminium electrolytics. A 68kMLA member describes his Quadra 800 as having "solid capacitors", explicitly contrasting it with the 840AV, and members of the same thread group the Quadra 800 with the Centris 650 and Quadra 650 as the "Wombat" board family — where two further members report tantalum and ceramic parts on their own boards. This is community observation, not an Apple statement, and it rests on fewer reports than the equivalent claim for the Centris 650. Check your own board before deciding not to recap it. Aluminium surface-mount electrolytics are small metal cans on a plastic base; tantalums are solid moulded blocks, usually amber or dark brown.
• Tantalums fail short. A shorted decoupling part drags its rail down and the supply shuts down or a fuse goes. Look for a cracked or scorched block, and for a rail that reads as a short to ground with the supply disconnected.
• The power supply is where the electrolytics are, and where the age-related failures happen.

Apple published no capacitor values for this machine. The Service Source contains no capacitance, working-voltage or designator data anywhere; every power fault in the symptom charts ends in "Replace power supply." Everything below is community data from a named source.

The Power Supply

The Quadra 800 uses the Delta SMP-220DB, Apple part number 614-0012. The same unit is fitted to the Macintosh Quadra 840AV and the Power Macintosh 8100/80.

It is built as five stacked sub-boards, four of which carry electrolytics. The list below was compiled by a 68kMLA member who dismantled a unit completely and recorded the designator, value and physical size of every part, and later corrected one entry (C253) in the same thread. All the electrolytics are 105 °C parts except the two bulk capacitors C1 and C2, which are 85 °C.

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

This is a secondary source and covers one physical unit. Read the markings on your own supply before ordering — and note that "SMP-220DP" appears on the boards while the unit as a whole is labelled SMP-220DB.

The 200 V bulk pair

C1 and C2 are in series across the rectified mains. That is how a 200 V part survives in a supply rated for 100–240 V input: on 230–240 V mains the DC bus sits at roughly 340 V, and only the series pair holds it off.

• Never fit a single capacitor in place of the pair. One 200 V part in that position will fail on European mains, violently.
• Replace both together with matched parts of the same value and voltage, or higher.
• These two are also the parts that hold their charge longest. Discharge them first and check them last.

Things That Are Not Capacitors

Recapping this supply frequently does not fix it. Two failures documented in the same thread are worth checking before you order parts:

• R955A and R955B on the control board — 180 Ω, 0.125 W. Both had burned open on one unit, taking the supply with them. The markings burn off, so there is no way to read the value from a failed part.
• ZD1 and ZD2 — 18 V zener diodes. If these are blown, the primary switching transistors have very likely gone too.
• A failed LM339N comparator on the control board brought one otherwise-dead unit straight back to life after a full recap had achieved nothing. The PS_ON signal connects directly to one of its pins.

Soft power behaviour

This supply is not an ATX unit and does not behave like one. PWR_ON latches on when it is pulled up to the +5 V trickle rail, and the supply will run with PWR_ON left unconnected. To shut it down you short PWR_ON to ground — the opposite of ATX. Bench-testing it with ATX assumptions will make a working supply look dead.

The +5 V trickle rail is the first useful measurement on a dead machine: present means the primary side is alive and the fault is downstream; absent means the mains input, the primary switcher or the standby circuit.

Replacement Procedure

1. Discharge the bulk capacitors and confirm with a meter.
2. Photograph every board before separating them. The five boards interlock and the inter-board pins only go back one way.
3. Desolder with a temperature-controlled iron and a pump or wick. The bulk capacitors sit on heavy copper and need dwell time.
4. Clean the pads with isopropyl alcohol. Expect generous, erratically placed silicone adhesive; soften it with isopropyl alcohol and cut it away with a scalpel rather than pulling.
5. Fit the replacements the right way round — on aluminium electrolytics the stripe marks the negative lead.
6. Reflow every joint you disturbed, including the inter-board pins, before the unit goes anywhere near mains.
7. Bring it up behind a series lamp — a 100 W or 200 W filament bulb in place of the fuse — on a dummy load, before connecting it to the logic board.

Use 105 °C, low-ESR parts rated for switching-supply ripple. See Recommended Tools.

Logic Board

No preventive recap is required if your board is a tantalum one. If a tantalum has failed, replace it with the same capacitance and generous derating: solid tantalums want about 50 % voltage derating, so a part on a 5 V rail needs a 10 V or higher rating and one on 12 V needs 25 V. Polymer parts are a good substitute and fail benignly.

Remember the polarity convention flips: on an aluminium electrolytic the stripe is negative; on a tantalum the bar is positive.

See Capacitor Failure Symptoms for what failure looks like elsewhere in the machine.

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 latched holder and is not soldered in.

Apple lists a battery check among the steps for intermittent shutdowns, because the cell is part of the soft-power circuit. A leaking cell will corrode the traces beneath the holder — see Battery Explosion, Capacitor or Corrosion Damage.

Electrical Specification and What Apple Does Not Publish

Apple's specification: 100–240 V AC, 50–60 Hz single phase, 200 W continuous. The supply is self-configuring, so there is no voltage selector to set wrongly.

Apple publishes no rail tolerance band and no power-supply adjustment procedure for this machine. There is no adjustment chapter in the Service Source and no potentiometer to turn. If a rail is out, the supply is faulty; there is nothing to trim.

Apple's symptom charts send the following to the power supply:

• Dead machine — black screen, fan not turning, LED not lit, after checking cables and the mains lead.
• Clicking, chirping or thumping noises.
• Intermittent shutdowns not explained by blocked vents or a flat battery. Apple notes that the thermal protection circuit will shut the machine down when the vents are obstructed, and that it recovers after 30 to 40 minutes — that is normal behaviour, not a fault.

Related Pages

• Macintosh Quadra 800
• Macintosh Quadra 800 Troubleshooting
• Macintosh Quadra 800 General Maintenance
• Macintosh Quadra 840AV Capacitor Replacement Guide — same power supply
• Capacitor Failure Symptoms
• Recommended Tools