Macintosh Centris 660AV General Maintenance

This page covers routine care for the Macintosh Centris 660AV, which Apple renamed the Quadra 660AV in October 1993 without changing the hardware. The two are documented together, and everything here applies to both.

Figures below come from Apple's Service Source for the Centris 660AV / Quadra 660AV and from Apple's Macintosh Quadra 840AV and Macintosh Centris 660AV Computers Developer Note, both hosted on this wiki.

What this machine is

This is not an ordinary 68040 Macintosh with extra sockets. Three pieces of hardware make it behave differently from a Centris 650 and are worth knowing before you diagnose anything:

• An AT&T DSP3210 digital signal processor. It does the sound work, so 16-bit stereo input and output at sample rates up to 48 kHz — with 44.1 kHz as the standard rate — depend on the DSP rather than on a conventional sound chip.
• A Peripheral Subsystem Controller (PSC) providing DMA between the processor buses and the peripherals.
• Composite and S-video in and out, plus a DAV (digital audio/video) connector that gives an accessory card direct access to YUV video data and digital sound. On the 660AV the DAV connector lives on the optional NuBus adapter card, not on the main board.

Apple's specification

Item	Figure
Processor	Motorola 68040 at 25 MHz, with built-in PMMU, FPU and 8 K cache
RAM	8 MB standard (4 MB soldered plus a 4 MB SIMM), expandable to 68 MB, 72-pin, 70 ns
ROM	2 MB — see the note below
VRAM	1 MB, two banks of 512 K soldered on the board; not expandable on the 660AV
PRAM	256 bytes
Expansion	One slot taking a NuBus, PDS or DAV card with the appropriate adapter
Ethernet	On-board, AUI-15 connector
Serial	One mini DIN-8 and one mini DIN-9 high-performance (GeoPort) modem port
Line voltage	100–240 VAC, 50–60 Hz
Maximum power	86 W

Apple's figures. One discrepancy is worth flagging: the Service Source specification table gives ROM as "1 MB soldered on logic board", while Apple's developer note says "identical ROM chips totalling 2 MB are provided with both models". The developer note is the more detailed document and is the figure used here.

VRAM is not expandable on the 660AV. Apple states that the Quadra 840AV's VRAM goes from 1 MB to 2 MB and the Centris 660AV's does not. A 660AV that will not take more video memory is behaving correctly.

Power supply

Apple service part 661-1688, shared with the Centris 610 and Quadra 610. Apple rates the machine at 86 W maximum, display excluded.

An expansion card in the single slot may draw at most +5 V 2.0 A, +12 V 175 mA and −12 V 150 mA. That is a real design limit; a card over it is a plausible cause of a machine that shuts down under load.

What Apple does and does not publish

Apple publishes no rail tolerance and no power-supply adjustment procedure for the Centris 660AV or Quadra 660AV. 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 dusty-filter fault

Before condemning a supply that will not start, take the cover off it and look at the filter mesh in front of the fan. These units accumulate a felt of dust there, the airflow stops, and the supply shuts down thermally. Clearing it has revived a good many "dead" 660AV supplies. That is a cleaning job, not a repair.

Recapping it

You may open this supply. Understand what is live in it first: it is mains-rectified, so with the cover off and the lead plugged in the fuse, input filter, bridge rectifier and reservoir capacitors sit at mains potential and hold a charge after the plug comes out. Unplug, discharge each large reservoir through a 1 kΩ / 5 W resistor, and confirm with a meter that it reads near zero before a tool goes near the primary side.

If your unit has two reservoir capacitors in series across the rectified mains, replace both together with matched parts. The series pair is how a 100–240 V supply holds off the ~340 V that 240 V mains rectifies to, using parts rated a couple of hundred volts each. A single capacitor in place of the pair will fail on European mains, violently.

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.

A flat battery on this machine takes the video with it

A dead or low-voltage PRAM cell can kill the built-in video on a 660AV entirely. The machine chimes, the drives run and the screen stays dark, which looks exactly like a failed logic board or a failed monitor. Apple documented the behaviour, and it is the single most useful thing to know about this model before you start swapping parts.

So on a 660AV with no picture, measure the battery first — before the video cable, before the monitor, before the logic board. Apple's own symptom chart also puts "check battery" among the first steps for a machine that will not power on, because a flat cell can stop the soft-power circuit latching.

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.

Add one item specific to this machine: the DAV / NuBus adapter card and its connector. If the machine has a card fitted through the angle adapter, reseat both the card and the adapter.

Capacitors

Thirteen surface-mount electrolytics on the logic board: eleven 47 µF 16 V and two 10 µF 16 V. That is the whole population. There are no 1 µF parts and no 50 V parts on this board — lists that include them are copied from a different machine.

Designators, the annotated board photograph and the procedure are on Macintosh Centris 660AV Capacitor Replacement Guide.

Apple published no capacitor values for this machine, so the figures above are community readings of physical boards rather than a manufacturer specification. Count the cans on your own board before ordering a kit.

Unlike the Centris 650, whose logic board is a tantalum-and-ceramic design, the 660AV board does carry aluminium surface-mount electrolytics and does leak. Audio faults come first, which on this machine means the DSP-driven sound path; then intermittent starting; then visible residue. See Capacitor Failure Symptoms.

Cleaning

Opening the case

Disconnect everything, press the release tabs at the rear and lift the cover off. No tools, no hidden screws.

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.

Two things specific to the 660AV's drive. Apple fitted an auto-inject SuperDrive to early units and a manual-inject drive later, and the instruction is to replace like for like. And the controller is unusual: Apple's developer note describes a new floppy controller based on Industry Standard 765 supporting both Apple's GCR format and DOS-compatible MFM. That is why a 660AV reads DOS discs that an older Macintosh will not.

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.

SCSI termination is automatic on this machine. Apple's developer note states that built-in circuitry terminates the internal and external SCSI cables automatically if no SCSI devices are connected. Do not add a terminator on the assumption that one is missing.

Things that are not faults

• VRAM that will not expand. The 660AV's 1 MB is soldered and fixed.
• No FPU to add. The 68040 in this machine already has one on-chip.
• A 16-bit video window that tops out at 512 × 384. That is the 660AV's published limit; 640 × 480 at 16 bits belongs to the Quadra 840AV.
• Sound that stops when DSP software is misbehaving. The sound path runs through the DSP on this machine, so it is not independent of software in the way it is on an ordinary 68040 Mac.

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 660AV
• Macintosh Centris 660AV Capacitor Replacement Guide
• Macintosh Centris 660AV Troubleshooting
• Macintosh Quadra 660AV
• Centris 660AV/Quadra 660AV Service Source
• Macintosh Quadra 840AV and Centris 660AV Developer Note
• Recommended Tools