Macintosh Centris 650 General Maintenance

The Centris 650 and Quadra 650 share one enclosure, logic board design and power supply.

This page covers routine care for the Macintosh Centris 650 and the Macintosh Quadra 650, which share a logic board design, a case and a power supply and which Apple documents together in one manual.

What this machine is

Apple's specification

Item	Centris 650	Quadra 650
Processor	Motorola 68040 at 25 MHz	Motorola 68040 at 33 MHz
RAM	4 or 8 MB standard, expandable to 132 MB, 72-pin SIMMs
ROM	1 MB
PRAM	256 bytes of non-volatile parameter memory
VRAM	512 K, expandable to 1 MB
Expansion	Three NuBus slots and one inline processor-direct slot
Ethernet	On-board Apple Ethernet port
Line voltage	100–240 VAC, 50–60 Hz
Maximum power	112 W, display excluded
Dimensions	6.0 × 13.0 × 16.5 in (152 × 330 × 419 mm), 25 lb (11.3 kg)

Apple's figures.

Power supply

Apple service part 661-0758, the same physical supply as the Macintosh IIvi, IIvx and Performa 600, and the same family as the IIcx, IIci and Quadra 700 supplies at a higher rating.

Apple's developer note prints the ratings for this supply, and they are worth having because they turn "is the supply all right?" into a measurement:

Apple's power supply ratings

Load	+5 V	+5 V TRKL	+12 V	−12 V	Total
Minimum	1.5 A	0 A	200 mA	0 A	9.9 W
Maximum	15 A	1 mA	2.5 A	600 mA	112 W
Peak	15 A	1 mA	6 A (12 s max)	600 mA	130 W

Those figures are Apple's for the supply used in this chassis family. They are corroborated from the other direction: 68kMLA members reading the rating plates of physical units record Apple part 614-0009 (Astec AA16870 / Delta SMP-120EB), fitted to the Centris 650, as +5 V 15 A, +12 V 2.5 A, −12 V 0.6 A with a 1 mA continuous +5 V trickle. 15 × 5 plus 2.5 × 12 plus 0.6 × 12 is 112 W exactly.

There is no −5 V rail. Apple's rating table has four outputs — +5 V, +5 V trickle, +12 V and −12 V — and no −5 V among them.

The +5 V trickle rail is the first useful go/no-go check on a dead machine. It is alive whenever the mains lead is in, whether the machine is switched on or not, because it powers the soft-power circuit and the clock. 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.

What Apple does and does not publish

Apple publishes no rail tolerance and no power-supply adjustment procedure for the Centris 650 or Quadra 650. The Service Source contains no acceptable-range table for any rail and no trimmer adjustment; every power fault in the symptom charts ends in "Replace power supply". The "+5 V 4.85–5.15 V / +12 V 11.9–12.7 V" table that circulates on pages of this era is Apple's Macintosh Plus procedure — genuine there, where it uses voltage test cable 077-0135 on the external floppy port — copied onto machines it was never written for. It has been removed from this page rather than reproduced, and no substitute has been invented.

What you can do instead is compare against a known load. Each rail at the logic-board power connector should sit close to its nominal value with the machine running and should not move when a drive spins up. A rail that is visibly low, or that sags under load, points at the supply. A rail that measures as a short to ground with the supply disconnected points at the logic board.

The series reservoir pair

68kMLA members' readings of a Centris 650 supply record C1 and C2 as a 470 µF 200 V pair on board SMP-120 EP. Those two are in series across the rectified mains, which is how a 100–240 V supply manages on 200 V parts: 240 V mains rectifies to about 340 V, and the series pair holds off 400 V between them.

• 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, matched, same value and voltage or higher.
• Do not "improve" the design with one 400 V part across both positions unless you also understand what the balancing resistors are doing.

Full supply list and procedure: Macintosh Centris 650 Capacitor Replacement Guide.

Battery

A 3.6 V lithium half-AA cell in a holder on the logic board keeps the real-time clock and parameter RAM alive with the machine unplugged.

Apple's check is a measurement, not a calendar. Set a meter to the 10 V DC range, put the positive probe on the positive end of the cell and the negative probe on the negative end, and replace the cell if it reads below 3.2 V. Apple publishes no replacement interval, and none is invented here: a cell above 3.2 V is doing its job and one below it should come out today whatever its age.

If it has leaked

This is a lithium cell, so neutralise with bicarbonate of soda, not vinegar. Vinegar is the right treatment for alkaline leakage, which is basic; it is the wrong treatment here and it adds water and chloride to an already corroded board. Use a paste of sodium bicarbonate and distilled water, rinse with distilled water, follow with isopropyl alcohol and dry thoroughly.

Then check the damage rather than assuming there is none:

• Inspect under magnification for traces that have gone dull, green or thin.
• Buzz out every track running away from the holder — corrosion travels under the solder mask and does not show from above.
• Check the underside of the board. Electrolyte wicks down through vias.

See Battery Explosion, Capacitor or Corrosion Damage and Battery Refurbishment.

Take the cell out before the machine goes into storage. That is not a service interval; it is the one measure that reliably prevents this damage.

Apple lists a battery check among the steps for start-up failures, and there is a reason for that: a flat or leaking cell can stop the soft-power circuit latching, so a machine that appears completely dead can be a battery fault rather than a supply fault.

Connectors and sockets

Oxidised contacts cause more intermittent faults on a machine this age than failed silicon does, and they are the cheapest thing to put right.

• SIMM sockets. Clean with isopropyl alcohol on a swab and reseat. Do not take an abrasive to a module's gold fingers — once you are through the plating, the base metal oxidises and then transfers to every socket the module touches.
• VRAM sockets. Same treatment. Video faults that come and go when the case is knocked usually start here.
• NuBus and PDS slots. Inspect for bent contacts and debris before a card goes home; check the card's edge fingers too.
• ROM SIMM socket, where one is fitted. A poorly seated ROM gives a machine that chimes and does nothing else.
• Logic-board power connector. Look for browning or a distorted housing. A discoloured power connector is a warning, not a cosmetic problem.
• ADB, serial, SCSI and floppy connectors. Reseat; check ribbon cables for cracked conductors where they fold.

A contact cleaner such as DeoxIT D5 earns its place on genuinely corroded contacts. It is not a preventive treatment and it does not belong on clean gold.

Capacitors: this board is the exception

The Centris 650 / Quadra 650 logic board is not an aluminium-electrolytic board. Two 68kMLA members who have had these boards in front of them report that it is populated with tantalum and ceramic parts. That means the creeping corrosion damage seen on the Centris 660AV, the Quadra 840AV and the compact Macs does not apply here, and that preventive recapping of the logic board is not indicated.

This is a community finding, not an Apple statement. Check your own board before taking anyone's word for it — and note what you are looking for, because the failure mode is different:

• Tantalums fail short, not open. A shorted decoupling tantalum pulls its rail down and the supply either shuts down or the machine will not start.
• Look for a cracked, split or scorched moulded block, not for weeping electrolyte.
• Confirm with a meter: with the supply disconnected, a rail that measures as a short to ground has a failed part on it.

The power supply does carry aluminium electrolytics, and it is the part of this machine that realistically needs recapping. See Macintosh Centris 650 Capacitor Replacement Guide.

If you do replace a tantalum, note that the bar marks the positive end — the opposite convention to an aluminium electrolytic's stripe — and derate generously: a solid tantalum on a 5 V rail wants a 10 V or higher rating, and one on 12 V wants 25 V.

Cleaning

Opening the case

Disconnect everything, press the release tabs at the rear and lift the cover off.

Inside

• Compressed air and an anti-static brush on the logic board, the supply and the fan. Hold the fan blade still while you blow it: spinning a fan with compressed air drives it as a generator and puts a reverse voltage back down its cable.
• Isopropyl alcohol (99 %) and a soft brush for grime, working outwards from each capacitor and from the battery holder.
• Check the underside of the board as well as the top. Both battery and capacitor electrolyte travel through vias.

Outside

• A damp microfibre cloth and mild detergent. No abrasives, no solvents — the texture on these shells does not survive either.
• ADB keyboards come apart for washing: keycaps off, warm soapy water, dry them completely, then clean the contacts with isopropyl alcohol.
• Mouse ball out, rollers scraped and wiped with isopropyl alcohol.

The platinum-grey plastics yellow with age. The discolouration is in the body of the plastic rather than on the surface, so cleaning will not shift it; see Retrobrite for what can be done and what it costs in brittleness.

Floppy drive

The 1.4 MB Apple SuperDrive is direct drive. It has no belt. Advice to fit a new belt to a sluggish or non-ejecting SuperDrive — including to the auto-inject version — is wrong: there is nothing there to replace. What these drives actually suffer is hardened grease on the head carriage and eject rails, dust in the mechanism, and dirty or worn heads. On manual-inject drives a worn eject gear is a genuine and common failure.

• Clean the heads with isopropyl alcohol on a lint-free swab, supporting the upper head arm so it is not sprung.
• If the rails are stiff, re-lubricate with a silicone grease — not white lithium grease, which gums up as it ages.
• If a disc will not eject, hold the mouse button down while switching the machine on to run a full eject cycle before taking anything apart.

See Macintosh Floppy Drive Maintenance.

Hard disk

The original SCSI mechanisms are past thirty years old and the usual failures are a stuck spindle, dried head-park grease and dead controller electronics. Solid-state replacements — BlueSCSI, ZuluSCSI, SCSI2SD — are quieter, cooler and considerably more reliable, and they let you keep the original drive on a shelf.

Whatever you fit, get the termination right: the drive at the end of the internal bus must be terminated, and the computer itself is always SCSI ID 7. See Macintosh HDD Maintenance.

Thermal

Keep the vents and the fan clear and the 68040 stays within its design. There is nothing to re-paste: the processor in these machines carries a passive heatsink where one is fitted at all, and there is no published thermal procedure for it.

What does matter is that the fan is turning. Apple's symptom charts distinguish "fan runs" from "fan does not run" in several places, and that distinction is the fastest branch in the whole fault tree.

Storage

• Take the battery out.
• Store dry and at room temperature — not a loft, not a garage.
• If the logic board comes out, bag it anti-statically and lay it flat.
• Nothing needs periodic running. "Power it up every few months to keep the capacitors formed" is repeated widely and supported nowhere for machines of this kind. The real hazard to a stored Macintosh is the cell in the battery holder, and removing it costs nothing.

Related pages

• Macintosh Centris 650
• Macintosh Centris 650 Capacitor Replacement Guide
• Macintosh Centris 650 Troubleshooting
• Macintosh Quadra 650
• Centris 650/Quadra 650 Service Source
• Macintosh Centris 610 Centris 650 and Quadra 800 Developer Note
• Recommended Tools