The boards are rev. 3 and what appears to be rev. 1½ since it has the 6290
ROM but not the 6291 and instead 6392-6395 and the rest. A peculiar thing
though; on the schematics (drawing 005922, sheet 4) the C6,7 decade counter
is connected to what looks like 128V on pin 14 (cpa). Is this actually the
60 hz pulse you are mentioning?
> The original design of the board cannot be operated using a switcher,
> because the NMI line is clocked at 60Hz from the AC input. Later versions
> of the board have a factory hack which eliminates this requirement. That
> might explain some of the problem. Good luck...
>
> Alex
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Received on Mon Oct 2 08:21:53 2006
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