Testing Gorf Ram PCB?

SpookySpaceKook

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Hey guys, I have a bad Gorf ram board which I know has one or more bad ram chips on it. I have horizontal thick lines on the screen and the players ship blows up right away on the screen. So I set the ram card on the bench, applied the +5, +12, and -5 volts to the board. None of the ram chips got hot so I took out my logic probe and checked out all the ram chip legs and all the chips tested exactly the same. If I have a bad ram chip, these are 4027 ram, why won't the bad chip or chips show up when using a logic probe? I guess my next step would be to piggyback a known good ram to each of the boards ram chips, one at a time and look for a change on the screen? Any good advice on testing ram chips? Thanks, Jon.
 
It could be a bad solder joint on any of the chips. I had one that would work if you put some pressure on the board but I never could find a bad joint. I had an extra board that worked so I never spent much time on it.:)
 
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