Tech: Bally -35 MPU - temperature related freeze-ups

Hi folks.
I rebuilt a corroded Bally -35 MPU and it ALMOST works. If it's cold,
it will boot up properly with 7 LED flashes "in the game" and 6
flashes on the bench with 12V and 5V attached to TP2 and TP5
respectively. The problem is, whether it is in the game or on the
bench, it freezes up shortly after boot up - like within 15 seconds or
so (in the game it will play the sound and start attract mode for a
few seconds, then freeze up at which point you can hear a 60hz hum).
If I let it cool off, it will do it the same way. If I try to boot up
immediately it will freeze up right away. If I let it cool slightly,
i.e. between 15 seconds to a minute or so, it will partially boot but
freeze up in mid-boot, the shorter cooling time, the sooner the freeze-
up.

On the bench I've hunted the board for hot spots and found that C5
gets too hot to touch if I leave power applied for a bit, and nearby
VR1 is slightly warm too, but not hot.

Reading through Clay's guide I can't find anything that points to
what's happening here. Searching RGP I found a couple references to
heat-related MPU stuff, but nothing similar enough to make a
correlation. I've checked and reseated all socketed chips. Headers &
connections might be suspect except that it happens identically on the
bench too with power attached to test points as per Clay's guide. The
test points aren't corroded or oxidized either.

There are a couple original chips with dark spots (oxidization) on the
legs. This may or may not be the problem, but I'm leaning away from
this being the likely cause because after re-seating a couple times it
still behaves identically. Besides, I'm not sure why one of the chips
might cause C5 to get so hot. Of course I don't know whether or not
it's wrong for C5 to become hot - maybe that's normal for all I know.

Can anybody help to point me in a next direction? I don't mind
replacing components even if I'd be re-replacing components I already
have in the corrosion rebuild process. Hell I'd redo the whole smash
if it would work. Seems like if I had an idea why the thing would be
locking up due to heat like it is, it might point to a more specific
plan of attack.

In case it matters, I also reinforced various traces that may have
been iffy, Especially the ground trace which was very flaky along the
bottom edge. Looking over the board and my rebuild work under
magnification, checking and re-checking again, it all looks solid even
if it ain't exactly purdy ("not purdy" being due to corrosion damage &
repair, not the soldering work which is pretty clean).

Thanks for any help.
.

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