Logic Chips and 12 volts

orion3311

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Is it a given or an almost given that if an input/output on a TTL chip sees 12v that its toast? I was working on a Space Invaders board yesterday and found it had a smashed trace, sending 12v into one of the address bus lines (A1). The board had no roms installed at the time. I know one chip got hot enough to pull my finger away (9233@F6) and I know the address buffer (74LS08 I think) saw 12v, but at this point both chips seem to at least have a signal although the boot isn't booting.

Just wondering if I should just shotgun those chips.

Also - the DMI/Hold pin on the CPU is low, causing the cpu to go into "disconnected" mode - is that normal for no roms? My test rom didn't seem to work but I need to replace the CPU and rom H sockets first I think.
 
Is it a given or an almost given that if an input/output on a TTL chip sees 12v that its toast? I was working on a Space Invaders board yesterday and found it had a smashed trace, sending 12v into one of the address bus lines (A1). The board had no roms installed at the time. I know one chip got hot enough to pull my finger away (9233@F6) and I know the address buffer (74LS08 I think) saw 12v, but at this point both chips seem to at least have a signal although the boot isn't booting.

Just wondering if I should just shotgun those chips.

Also - the DMI/Hold pin on the CPU is low, causing the cpu to go into "disconnected" mode - is that normal for no roms? My test rom didn't seem to work but I need to replace the CPU and rom H sockets first I think.

It could definately kill chips, but I've seen them survive, too. I think a lot depends on the duration of time they were pumped with 12V. On several occasions I've had Atari games in the shop with monitor issues. When a game is dropped off to me, I always do a quick "go through". One thing I do is meter the power supplies. Numerous times I've had the A/R II boards pumping 8-14VDC down the 5VDC rail....and the gameboard is working just fine. Now, how long will it work like that? Who knows?...but it can't be good.

Edward
 
if it just the input/output pin, yes, it will toast them. there's also possibility that the next one after that chip is also broken.
 
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