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Macintosh LC 475 General Maintenance

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Mac LC 475 Recap Guide
Macintosh LC 475 / Quadra 605 logic board 820-0364-A, annotated by Recap-a-Mac with the value of each electrolytic capacitor.

Routine care for the Macintosh LC 475, whose logic board (820-0364-A, 1993) is also used in the Macintosh Quadra 605; Apple's Module Identification gives one service logic board, 661-1732, for the Quadra 605, LC 475, Macintosh Performa 475 and 476.[1][2][3][4] The case, power supply, battery and take-apart procedure are shared with the rest of the LC family.

The machine in brief

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Macintosh LC 475 and Quadra 605 (Apple)
Item Figure
Processor Motorola 68LC040 at 25 MHz, in a socket; no FPU
RAM 4 MB on the board plus one 72-pin SIMM socket; 4 MB or 8 MB standard, expandable to 36 MB (80 ns or faster)
ROM 1 MB, soldered
VRAM Two 256K VRAM SIMMs, upgradable to 1 MB (two 512K SIMMs)
Expansion One slot for 96-pin LC II or 114-pin LC III cards; not a processor-direct slot
Sound Mono input; stereo output
Power 100-240 V AC, automatically configured; 47-63 Hz (LC 475), 50-60 Hz (Quadra 605); Quadra 605 26 W maximum
Size and weight 3.0 × 12.2 × 15.0 in (7.7 × 31.0 × 38.2 cm); 8.8 lb (4.0 kg)

Figures from the Service Source and the Developer Note.[4][5]

Three things that look like faults are not. The 68LC040 has no floating-point unit, so software that needs one will not run on a standard machine. Two small VRAM SIMMs are the factory fit. The expansion slot is not connected to the processor and runs at 16 MHz, so accelerators, FPU cards and cache cards made for the LC II and LC III do not work in it.[5][4]

Opening the case

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  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.[4]

The fan has its own cable to the logic board: disconnect it, release the plastic latches and lift the fan out. Apple's fan procedure, written for the LC II and LC III, says to refit the fan logo side down, or it may damage the computer.[4]

Cleaning

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Blow dust out of the logic board, power supply and fan with compressed air, holding the fan still. Clean residue with isopropyl alcohol and a soft brush, and look at both sides of the board around the capacitors and the battery holder. See Capacitor Failure Symptoms.

Power supply

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Recap-a-Mac treats the LC, LC II, LC III, LC 475 and Quadra 605 supplies as one design, prone to leakage and failures in its smaller capacitors.[6] Apple's exploded view for the family gives the supply as part 661-1733, and it accepts 100-240 V AC without a selector.[4] To remove it, disconnect its cable from the logic board, release the two latches that hold its front end to the bottom case, and lift it out.[4]

Apple's Service Source has no Adjustments chapter and gives no rail voltages or tolerances for this family; its power symptoms end in "Replace power supply".[4] Capacitor values for the supply are on Macintosh LC Capacitor Replacement Guide.

The supply runs from the mains. Its primary side, including the bulk capacitor, is at mains potential when plugged in, and the bulk capacitor stays charged after the plug is pulled. Unplug it, wait, and measure across the bulk capacitor before working on the primary side.

PRAM battery

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Apple's part is lithium battery 742-0011 in a clip-in holder; EveryMac gives it as 3.6 V.[4][7] Apple's check: set the meter to the 10 V DC range, probe the two ends of the cell, and replace it if it reads below 3.0 V.[4] To open the holder, push a small flat-blade screwdriver down into the top of the holder until the side tab pushes out, then repeat at the other end.[4]

Recap-a-Mac fitted a CR2032 holder in place of the original on its example board.[3] A CR2032 is a nominal 3 V cell, the same as Apple's replace-below figure.

A leaking lithium cell is neutralised with bicarbonate of soda, not vinegar. After cleaning, check the tracks around the holder for continuity and look at the underside of the board. See Battery Explosion, Capacitor or Corrosion Damage and Battery Refurbishment.

Capacitors

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The 820-0364-A logic board has eleven surface-mount electrolytics: nine 47 µF 16 V and two 100 µF 6.3 V.[3] The LC III's reversed −5 V capacitor does not apply: Doug Brown found the LC 475 board wired the correct way round.[8] The photograph and procedure are on Macintosh LC 475 Capacitor Replacement Guide.

Processor

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The 68LC040 is in a socket and can be replaced by a full 68040 to gain an FPU.[5] Apple removes it with a processor removal tool, lifting the handle up (pressing down can damage parts on the board) and prying each side only slightly so the pins do not bend. The EMI clips on the underside of the board flex easily and should not take heavy pressure.[4]

Floppy drive

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The LC 475 and Quadra 605 shipped with either the auto-inject Apple SuperDrive or the manual-insert version, and Apple's instruction is to replace drives like for like. Remove the dust shield, if present, before fitting a replacement auto-inject drive.[4] Apple's cures for a stuck disk are to hold the mouse button down while switching on, or to push a straightened paper clip into the hole beside the slot.[4] See Macintosh Floppy Drive Maintenance.

Hard disk

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The internal SCSI drive carries the internal termination; Apple's chart for a machine that works with an internal or an external SCSI device but not both includes checking that the terminator is installed on the internal drive and that the external chain is terminated.[4] See Macintosh HDD Maintenance for drive care and replacements.

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References

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  1. ↑ Apple Computer, Module Identification, part number 072-8124, June 1994, section 1.5.11 (PDF p. 85): "Macintosh Quadra 605, LC 475, Performa 475, 476 Logic Board", Apple P/N 661-1732. Hosted as File:Apple Service Module Identification Manual (June 1994).pdf.
  2. ↑ Apple Computer, Macintosh Performa 400 Series Service Source, File:Performa 400 series.pdf; see Macintosh Performa 400 Series Service Source. Specifications, PDF pp. 3-14: Performa 475/476 with a 25 MHz 68LC040, 4 or 8 MB to 36 MB, 1 MB ROM.
  3. ↑ 3.0 3.1 3.2 Macintosh LC475 & Quadra 605, Recap-a-Mac—link(accessed 2026-09-30) Annotated photograph of logic board 820-0364-A, hosted here as File:Mac LC 475 Recap Guide.jpg: 9 × 47 µF 16 V and 2 × 100 µF 6.3 V; the author replaced the ½AA battery holder with a CR2032 holder.
  4. ↑ 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 4.11 4.12 4.13 4.14 Apple Computer, Macintosh LC Series/Quadra 605 Service Source (1995), File:Quadra_605.lc_series.pdf; see Macintosh LC Series/ Quadra 605 Service Source. PDF page numbers: Specifications pp. 6-17; Symptom Charts pp. 20-36 (SCSI p. 28); Top Cover p. 38; Fan pp. 44-45; Floppy Drive pp. 48-52; Power Supply pp. 53-54; Logic Board pp. 55-63; Macintosh Processor Upgrade pp. 87-104 (processor removal cautions p. 94; EMI clips p. 100); Battery Verification p. 107; Battery Replacement pp. 108-110; Exploded View p. 112.
  5. ↑ 5.0 5.1 5.2 Apple Computer, Macintosh LC 475 and Macintosh Quadra 605 Developer Note (1993), File:Macintosh LC 475 and Quadra 605 Developer Note.pdf; see Macintosh LC 475 and Quadra 605 Developer Note. Printed pages: p. 2 (features: 1 MB ROM soldered); pp. 7-13 (RAM and VRAM); p. 19 (expansion slot is not a PDS); p. 22 (68LC040 in a socket); p. 39 (cards that do not work).
  6. ↑ Macintosh LC Power Supply (For LC, LC II, LC III, LC 475 and Quadra 605), Recap-a-Mac—link(accessed 2026-09-30)
  7. ↑ Apple Macintosh LC 475 Specs, EveryMac—link(accessed 2026-09-30) Battery type 3.6 V lithium.
  8. ↑ Doug Brown, "The capacitor that Apple soldered incorrectly at the factory", 26 November 2024.


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