14 Nov
2007
14 Nov
'07
4:13 p.m.
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
IIRC that '38 is part of the vidro drive circuit (at least it is in the
Mac+). I can't rememebr what the LAG chip does, it's one of the PALs I think.
My first thought, though is 'why those 2 particular chips only?' My
_guess_ is that the author of said book has had to repair a couple of
Macs danaged by incorrect CRT discharging, and those where the chips he
found had failed. Next time it might be something else.
former sounds like it might be fairly standard. The
latter sounds
The 74LS38 is a standard TTL part, a quad 2-input NAND with open collector
outputs. It's a very common IC.
like it may be one of the custom programmed PALs or
GALs or whatever
that Tony was writing about.
It is.
-tony