4 Feb
2008
4 Feb
'08
10:01 p.m.
Just to follow up on a very old thread -- I finally got a replacement
LAG for my 512k Mac (thanks to a very helpful list member with a GAL
programmer) and after replacing it, the Mac is once again functioning.
So if you do accidentally do what I did (discharge the CRT to the main
chassis) and you end up with a very long, drawn out boot beep, the LAG
is quite possibly the culprit.
Thanks once again to all you helpful folks. You've been, well, helpful :).
- Josh
That particular failure is documented in Larry
Pina's "Macintosh Repair
and Upgrade Secrets" and probably in "The Dead Mac Scrolls" as well.
I'd
look it up for you, but I don't have my books with me here.
Okay, I'm home, I have my books. It says on page 98 that discharging
the CRT without a big honking resistor may blow a 74LS38N (U2) on the
analog board and the LAG chip on the logic board. The former sounds
like it might be fairly standard. The latter sounds like it may be
one of the custom programmed PALs or GALs or whatever that Tony was
writing about.
I wouldn't be surprised if folks had already figured out all the
internal logic for the various Mac 128/512/Plus chips though. Finding
it might be a bit of a challenge.
OTOH, the LAG chip may be fine and it could be U2 on the analog board
that has the problem.
Jeff Walther