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Apple Macintosh LC 575 Logic Board Upgrade

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Macintosh LC 575 Logic Board Upgrade
Macintosh LC 575 logic board 661-0867 (Apple Module Identification)
The LC 575 logic board, service part 661-0867 (Apple, Module Identification, 1994)
Manufacturer Apple Computer
Type Logic board upgrade
Compatible Macintosh LC 520, Macintosh LC 550

The Macintosh LC 575 Logic Board Upgrade is Apple's upgrade that turns a Macintosh LC 520 or Macintosh LC 550 into a Macintosh LC 575 by replacing the logic board. AppleFacts 10.94 lists it under the LC 520 and LC 550: they "can be upgraded to the Macintosh LC 575 with the purchase of the Macintosh LC 575 Logic Board Upgrade".[1] The LC 575 has the mechanical design of the LC 520 and the electrical design of the Macintosh LC 475.[2]

What changes

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LC 520 and LC 575 logic boards
LC 520 LC 575
Processor 68030, 25 MHz 68LC040, 33 MHz[3]
VRAM 512 KB–768 KB 512 KB–1 MB[2]
Communication slot No Yes[4]
Ethernet No Optional, internal[2]
Battery held by hook-and-loop fastener No Yes[4]
Service part 661-0812 661-0867[5]

The LC 550 board sits between the two, with a 68030 at 33 MHz; like the LC 520 board it lacks the communications slot and the hook-and-loop battery mounting.[3][4] The LC 575 uses the same type of VRAM SIMM as the LC 520, so the old board's VRAM can be moved across, provided both sockets hold SIMMs of the same size.[2]

The LC 550 and LC 575 shipped with the manual-inject 1.4 MB SuperDrive, a revised chassis harness without a floppy drive adapter and the caddyless CD 300+ drive. The newer harness can be fitted to an LC 520 or LC 550, but it needs the manual-inject floppy drive and the caddyless CD-ROM drive.[4]

Fitting the board

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On these models the logic board slides out of the back of the case once the I/O door is off. Apple's Service Source says that "although upgrading the logic board is now extremely easy", the ESD precautions still apply: a grounded workbench pad and a grounding wrist strap.[6]

  1. Remove the two screws from the I/O door, push down on its two tabs and take the door off.
  2. Pull the logic board out of the rear of the computer.
  3. Move the VRAM SIMMs across if they are being kept.[2]
  4. Slide the LC 575 board in and refit the I/O door.

Apple's PowerPC upgrade for the LC 520 and LC 550 was built on the same board: it consisted of an LC 575 logic board, the PowerPC Upgrade Card, a new rear panel and the 575 product ID label, installed by following the LC 575 Macintosh Processor Upgrade procedure with the 575 board, rear panel and label substituted.[7]

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References

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  1. ↑ Apple Computer, AppleFacts 10.94 (October 1994), Macintosh LC 575 entry, "Upgrade information". vintageapple.org (retrieved 2026-10-04).
  2. ↑ 2.0 2.1 2.2 2.3 2.4 Apple Computer, Macintosh LC 575 developer note, chapter 1: "Whereas the mechanical design of the Macintosh LC 575 computer is like that of the Macintosh LC 520, its electrical design is similar to that of the Macintosh LC 475" (p. 2); Table 1-1, comparison of the LC 520, LC 475 and LC 575 (p. 3); "Video RAM": the VRAM SIMMs "are the same type as those used in the Macintosh LC 520 and Macintosh LC 475 models", and both sockets must hold SIMMs of the same size (p. 12). Hosted as File:Macintosh_LC_575_Developer_Note.pdf; see Macintosh LC 575 Developer Note.
  3. ↑ 3.0 3.1 Apple Computer, Macintosh LC 520, Macintosh LC 550, Macintosh LC 575 Service Source, Specifications, Processor - 1 (PDF p. 7): LC 520 68030 at 25 MHz, LC 550 68030 at 33 MHz, LC 575 68LC040 at 33 MHz. Hosted as File:Lc_520.550.575.pdf; see Macintosh LC 520/550/575 Service Source.
  4. ↑ 4.0 4.1 4.2 4.3 Macintosh LC 520, 550, 575 Service Source, Basics, Product Information - 2 and 3 (PDF pp. 4-5): identifying features of the LC 575 board, the newer drives on the LC 550 and LC 575, and the chassis harness compatibility note.
  5. ↑ Apple Computer, Module Identification, PN 072-8124, June 1994: Macintosh LC 520 Logic Board 661-0812, p. 1.11.5 (PDF p. 115); Macintosh LC 575 Logic Board, 33 MHz, 661-0867, p. 1.11.7 (PDF p. 117), with the note to return the board without VRAM or DRAM SIMMs and to leave any ROM SIMM in place. Hosted as File:Apple Module Identification (PN 072-8124, June 1994).pdf; see Apple Module Identification Manual (1994).
  6. ↑ Macintosh LC 520, 550, 575 Service Source, Take Apart: I/O Door - 13 (remove the two screws, push down on the two tabs); Logic Board - 14 and 15 (PDF pp. 51-52).
  7. ↑ Macintosh LC 520, 550, 575 Service Source, Upgrades, Macintosh Processor Upgrade - 3 (PDF p. 101).


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