Macintosh LC 475 General Maintenance

This page covers routine care for the Macintosh LC 475 (logic board 820-0364-A, 1993), which is the same board as the Macintosh Quadra 605 and the Macintosh Performa 475/476. The chassis, power supply, battery and take-apart procedure are shared with the rest of the LC "pizza box" family.

Figures below come from Apple's Service Source for the LC series and Quadra 605 and from Apple's Macintosh LC 475 and Macintosh Quadra 605 Developer Note, both hosted on this wiki.

What this machine is

Apple's specification for the LC 475 and Quadra 605

Item	Figure
Processor	Motorola 68LC040 at 25 MHz, 32-bit internal data bus, burst-mode RAM access
DRAM	4 MB or 8 MB standard, expandable to 36 MB (80 ns or faster SIMMs)
ROM	512 K, expandable to 1 MB
VRAM	Two 256 K VRAM SIMMs, upgradable to 1 MB
Expansion	114-pin slot for 030/040 expansion cards
Sound	Monaural 8-bit input; stereo output — the first in this family
Frequency	47–63 Hz (LC series) / 50–60 Hz (Quadra 605)
Dimensions	3.0 × 12.2 × 15.0 in (7.7 × 31.0 × 38.2 cm), 8.8 lb (4.0 kg)

Apple's figures. Three of them are regularly misread as faults:

• No FPU. The 68LC040 has no floating-point unit. Software that requires one refuses to run on a standard machine, and that is a specification, not a fault.
• Two small VRAM modules is the factory configuration, not somebody's bodge: Apple ships a pair of 256 K VRAM SIMMs, upgradable to 1 MB.
• The expansion slot will not take an accelerator. Apple states that the 114-pin slot accepts LC-compatible I/O, display, network and video-capture cards but does not support 030 processor accelerator or cache cards, and Apple's developer note is blunter still — the slot is not a processor-direct slot, and cards that assume direct 68030 bus behaviour will not work in it.

Power supply

Every "pizza box" machine in this family — LC, LC II, LC III, LC III+, LC 475 and Quadra 605 — takes the same power supply, which Apple lists as a single service part, 661-1733. It is a universal auto-ranging switch-mode unit covering 100–240 VAC, so there is no voltage selector to set wrongly and no separate 120 V and 230 V board to confuse.

Apple's electrical specification

Item	Figure
Line voltage	100–240 VAC, automatically configured
Frequency	47–63 Hz (LC 475) / 50–60 Hz (Quadra 605)
Maximum power, Quadra 605	26 W, monitor excluded

Note what that figure is: the machine's maximum consumption, not the supply's rating. The same 661-1733 supply is fitted to a 50 W LC and to a 26 W Quadra 605.

Apple publishes 26 W for the Quadra 605 and no separate figure for the LC 475; the two are the same board in the same case. The "30 W power supply" figure sometimes quoted for the LC 475 is Apple's LC III maximum-power number, which belongs to a different machine and is a consumption figure rather than a supply rating in any case.

What Apple does and does not publish

Apple publishes no rail tolerance and no power-supply adjustment procedure for this machine. The Service Source carries no acceptable-range table for the +5 V, +12 V or −5 V rails 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.

What you can do instead is compare against a known load. With the machine running, each rail at the logic-board power connector should sit close to its nominal value 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.

Recapping it

You are allowed to open this supply — tired electrolytics in it are one of the commonest reasons one of these machines will not start. Understand what is live inside first. It is fed straight from the mains, so with the cover off and the lead in, the fuse, input filter, bridge rectifier and bulk capacitor all sit at mains potential. The bulk capacitor charges to roughly the peak of the incoming waveform — about 170 V on 120 V mains, about 340 V on 230 V mains — and holds a useful fraction of that after the plug comes out. Unplug, wait, then measure across the bulk capacitor and confirm it reads a few volts before a tool goes near the primary side.

Apple bought this supply from several vendors and their capacitor complements differ, so read the maker's label before ordering parts. The per-variant lists are on Macintosh LC Capacitor Replacement Guide.

Removing it: disconnect the power supply cable from the logic board, release the two latches that hold the front end of the supply to the bottom case, and lift it out.

PRAM battery

Apple's part is a 3.6 V lithium half-AA cell, part number 742-0011, in a clip-in holder on the logic board. It appears under that number in the exploded view Apple prints for the whole LC series and the Quadra 605.

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 3.0 V. Apple publishes no replacement interval for this battery and none is given here: a cell above 3.0 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 an alkaline cell, whose leakage 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 instead of 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.
• Look at the underside of the board. Electrolyte wicks down through vias and comes out the other side.

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.

The CR2032 question

Replacing the original holder with a CR2032 coin-cell holder is a popular modification because CR2032s are cheap and available anywhere. Be clear about the trade-off first: a CR2032 is a nominal 3.0 V cell, which is exactly the voltage at which Apple's own procedure says to throw the battery away. A fresh CR2032 therefore starts life at Apple's replace-now threshold and falls from there. Expect a shorter useful life, and on a marginal machine expect PRAM that does not hold.

A 3.6 V lithium half-AA in a holder — rather than soldered in — gives you the original voltage with the same convenience.

Cleaning

Opening the case

1. Disconnect everything.
2. Remove the case screw if one is fitted. Not every machine has one.
3. Lift the tabs at the back of the lid and lift the top cover straight up.

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.
• Look at the underside of the board too. 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 about it and what it costs in brittleness.

Fan

The fan is a separate part with its own cable to the logic board: disconnect the cable, release the plastic latches, lift it out. Fit it back logo side down — Apple prints this as a caution because a fan installed the other way up blows the wrong way and may damage the computer.

Connectors and sockets

Oxidised contacts are the commonest cause of intermittent faults on a machine this age, and the cheapest to put right.

• SIMM sockets. Clean with isopropyl alcohol on a swab and reseat. Do not take an abrasive to a SIMM'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.
• Expansion slot. Check for bent contacts and debris before a card goes home.
• Logic-board power connector. Look for browning or a distorted housing. A discoloured power connector is a warning, not a cosmetic problem.
• SCSI and floppy headers. Reseat, and check the ribbon for cracked conductors where it folds.

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.

Working around the processor

The 68LC040 is socketed, and swapping it for a full 68040 to gain an FPU is a popular upgrade. Apple's own procedure removes the processor with a dedicated processor removal tool, which Apple sold as a separate service part. There is a reason for that: levering a PGA package out with a screwdriver bends pins and cracks board corners, and a cracked corner on this board takes traces with it.

If you do not have the tool, leave the processor in place. It is not a part that needs periodic attention, and the machine is no worse for it.

Capacitors

Eleven surface-mount electrolytics on logic board 820-0364-A: nine 47 µF 16 V and two 100 µF 6.3 V. Two independent community sources — Recap-a-Mac's annotated photograph of the board and MacDat's reference list — give the same complement.

There are no 10 µF parts on this board. Lists that put four of them on it are copied from a different machine. Designators, the board photograph and the full procedure are on Macintosh LC 475 Capacitor Replacement Guide.

Unlike the LC III, this board's bulk capacitor on the −5 V rail is wired the correct way round, so an 820-0364 with serial-port faults after a recap has a genuine fault rather than the LC III's silkscreen error.

See Capacitor Failure Symptoms for what a seeping surface-mount electrolytic looks like before it looks like anything.

Floppy drive

The LC 475 and Quadra 605 shipped with either the auto-inject 1.4 MB SuperDrive or the manual-inject version, and Apple's instruction is to replace drives like for like.

Neither is belt driven. The Apple SuperDrive is a direct-drive mechanism and there is no belt in it to perish or replace. What goes wrong is hardened grease on the head carriage and eject rails, dust, and dirty or worn heads.

• Heads: isopropyl alcohol on a lint-free swab, supporting the upper head arm.
• Stiff rails: a silicone grease, not white lithium grease.
• Before fitting a replacement SuperDrive, remove the dust shield if one is present.

See Macintosh Floppy Drive Maintenance.

Hard disk

The original SCSI mechanisms are 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 as a spare.

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

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 LC 475
• Macintosh LC 475 Capacitor Replacement Guide
• Macintosh LC 475 Troubleshooting
• Macintosh Quadra 605
• Macintosh LC Series/ Quadra 605 Service Source
• Macintosh LC 475 and Quadra 605 Developer Note
• Recommended Tools