OK, I guess since I already have a reply to my "introduce myself" post I'm a full-fledged member now, so it's down to business,
(thanks Mark)
Warning: This is cross-posted from RGP, but I just discovered this forum a few minutes ago so hopefully you'll forgive me.
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 repeat the problem 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.
