Well I got the board running with the fluke. Looks like a bad 6502 socket was the culprit.
Now I have a problem with the ZOUT. Hooked up to the scope nothing is being hidden.
Going through things I verified that the appropriate signals are getting to the Z section of the outputs. But the ZN3904 @ Q8 is dropping it all to ground. I pulled Q8 and get normal Z function.
Tracing back the input to Q8 I see that !ZBLANK controls it. This is in turn controlled by !WNDWBLK and part of the stat system.
Checking !WNDWBLK I see that it is always low.
Any ideas on how to debug this area? !LST & !HST which feed it appear to be working fine.
I am betting some cap / resistor / diode / comparator / opamp in the X or Y section of the window hardware has died and is causing this but can't really see anything.
David
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Received on Fri Jul 4 05:21:24 2003
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