Re: Debuging wndwblk in battlezone

I would definitely try the opamps. Easy check, they are used as comparator, so the output is always VCC or GND, depending on which input voltage is higher, - input higher than + input will make the ouput is GND, + input will make the output go VCC.
  ----- Original Message -----
  From: David Shoemaker
  To: vectorlist@vectorlist.org
  Sent: Friday, July 04, 2003 11:21 AM
  Subject: VECTOR: Debuging wndwblk in battlezone

  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 12:03:19 2003