Macintosh Classic / Classic II Troubleshooting: Difference between revisions
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Expand troubleshooting: add common faults (RIFA/PRAM battery/recap/ROM-disk/SCSI), cited from 68kMLA/recapamac/etc. |
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* If the screen shows garbage or freezes early in boot, check for shorted capacitors | * If the screen shows garbage or freezes early in boot, check for shorted capacitors | ||
* Trace repair may be required for extensive battery leakage (especially under RAM and ROM sockets) | * Trace repair may be required for extensive battery leakage (especially under RAM and ROM sockets) | ||
== Booting from the ROM disk (Classic) == | |||
The original Macintosh Classic holds a minimal copy of System 6.0.3 in ROM. Holding '''⌘ Command + Option + X + O''' at power-on boots this ROM disk (the letters refer to the Classic's "XO" codename). This is a useful diagnostic: if the machine boots the ROM disk but not from a drive, the logic board and video are working and the fault is in the storage or the system software rather than the core logic.<ref name="classic_src">[https://68kmla.org/ 68kMLA] threads on the Macintosh Classic (ROM-disk boot, recap and checkerboard faults) and [https://blog.gingerbeardman.com/2021/02/20/macintosh-classic-logic-board-recap/ "Macintosh Classic logic board recap"], gingerbeardman. Source for the ⌘-Option-X-O ROM boot and the surface-mount capacitor leakage.</ref> | |||
== ⚠️ Surface-mount capacitor leakage (recap first) == | |||
The Classic, Classic II (and the Macintosh Portable) are notorious for leaking surface-mount electrolytic capacitors. The electrolyte creeps like honey across the logic and analog boards, dries to a film, and corrodes traces, pads and vias — it is the single most common cause of Classic/Classic II faults (no boot, simasimac, distorted or crackly sound, dead audio). '''Recap and clean the board before any other diagnosis.''' Watch the capacitor next to the SCSI controller in particular: its leakage shorts the SCSI bus. After a recap, a machine that will not boot the ROM disk (⌘-Option-X-O) usually has a recap error — a wrong value, reversed polarity, or a bridged or lifted pad.<ref name="classic_src" /> | |||
== Classic II specifics == | |||
The Classic II uses a 16 MHz 68030 on an LC-derived logic board and is even more prone to capacitor leakage than the original Classic; distorted or "farting" sound is a hallmark of its leaked audio-filter capacitors. It is the same hardware as the '''[[Macintosh Performa 200]]'''. | |||
== References == | |||
<references /> | |||
== Related Resources == | == Related Resources == | ||