(Topic ID: 200481)

System 11 MPU no VMA signal

By ekthoren

6 years ago



Topic Stats

  • 3 posts
  • 2 Pinsiders participating
  • Latest reply 6 years ago by ekthoren
  • Topic is favorited by 1 Pinsider

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#1 6 years ago

I need some help. I have a system 11 (not an a, b, or c the first one) board. It does boot but not properly. I have Leon’s test eprom. When I hook it up it does not cycle through the tests. When I check the signals on U15 6802 chip I get only .11volts on pin 5 VMA and 5.0 volts on pin 37 signal “E”. Pins 2,3,8,35, and 40 all have 5.0volts as does my working system 11 board that I’m comparing this too. Pin 39 is 2.0volts on both boards. I’m using a dmm not a logic probe. So I’ve changed u37 and u32 and their is no change. I’ve also changed u15 and their is no change. I’m not sure where to go from here and any help would be appreciated.

#3 6 years ago

Ok disregard this thread. I somehow managed to kill the 6802 when I was doing testing because when I replaced it (again) the VMA signal came back. Now I’m back to my original sound problem which I never mentioned in this thread.

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