Editing Apple Lisa Troubleshooting (section)

== Boot self-test and error codes ==

The Lisa boot ROM runs a self-test and, on a fault, shows a '''numeric error code''' and draws a '''cross (X) over the icon of the failing board'''. Useful codes:

* '''40''' — CPU-board / MMU fault (a failed MMU register test loops endlessly; the CRT goes blank once warm).
* '''57''' — disk-controller fault.

The card-based design makes diagnosis a matter of swapping the '''CPU, memory and I/O boards'''; almost everything is user-replaceable except the CRT and video board.<ref name="lisa">[https://lisafaq.sunder.net/single.html The Apple Lisa FAQ]; [https://tinkerdifferent.com/threads/lisa-2-repair-journey.1151/ Lisa 2 repair journey], TinkerDifferent; [https://www.classic-computers.org.nz/blog/2011-03-05-rejuvenating-a-lisa2-10.htm Rejuvenating an Apple Lisa 2/10], Tezza's Classic Computers; and the Apple Lisa Do-It-Yourself Guide. Source for the I/O-board battery-pack leakage, the PSU failure, the Twiggy-drive unreliability, and the boot-ROM error codes (40 = CPU/MMU, 57 = disk controller).</ref>