Dodgy Sprint2 PCBs

Hi!
I recently picked up two Sprint2 machines that need some work. Both PCBs
have had a AC/DC Regulator bypass operation and one board has a burned TDA
1004 audio amplifier. So, now I've pulled them out of the cabs and hooked
them up to a test monitor and supplying DC 5v directly onto the board
(ignoring the 16 and 25VAC part) and both PCBs produce a nice picture
consisting of random characters. They sometimes actually have cars jumping
around among the random characters, especially if I pull out some ROMs.

Someone told me that Sprint2 PCBs wont run out of the cabinet unless the
Coin switch pins are grounded on the PCB so I tried that aswell, but to no
avail.

My questions are:

* What would a working PCB show when just applying the 5V without the
cabinet harness attached?

* Supposed my PCBs are bad, where should I start digging?

Thanks,

Joel
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Received on Sun Oct 1 17:12:41 2006