How not to fix a classic mac (or: fried logic boards)

der Mouse mouse at Rodents.Montreal.QC.CA
Tue Nov 13 15:31:31 CST 2007

> The problem is thst most of the logic is in HAL chips (Hard Array
> Logic -- mask programmed gate arrays with the saem architecture as a
> PAL).  And AFAIK there's no way to read out the 'fuse map' from a HAL
> (certainly I've never managed it).  So I don't have the logic
> equations, which makes troubleshooting, and indeed repair, a little
> hard.

I don't know PAL/HAL chips, but if you have reason to think the circuit
is combinatorial, it's easy enough to just exhaustively probe its truth
table, and once you have that, you don't care how it's built up in
terms of gates (except, I suppose, for cases where delay times and
output glitches matter).

Of course, if it's *not* combinatorial, it gets more interesting.  And
I suppose all the interesting stuff isn't....

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