(Topic ID: 168965)

Switch matrix row short

By wingnut

7 years ago



Topic Stats

  • 2 posts
  • 1 Pinsider participating
  • Latest reply 7 years ago by wingnut
  • No one calls this topic a favorite

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#1 7 years ago

Hey all

I just picked up a new machine and I'm fighting a switch matrix issue. What I'm seeing is that any switch on row 0 (i0) and row 1(i1) always fire together. This also happens with rows 5 and 6. It looks like on this X's and O's the switch matrix feeds straight into a 6821.

Thus far I've tried ohming out the rows and they don't seem truly shorted, and I've also tried swapping the 2 6821s on the mpu board. I've also went through the switches looking for issues and am wondering if there are other places to focus my efforts? Is a row short likely a diode issue?

Thanks

1 week later
#2 7 years ago

This one got even weirder then got better. What it boils down to was the MPU board, after digging and cleaning a lot of connections I tried reinstalling the MPU and at one point it just stopped coming up. Given the level of acid damage from a leaking battery I was feeling pretty bleak but the leaks and corrosion were mostly isolated from the switch matrix which made little sense that it would have been the issue. I tried the standard reseating of everything and connectors and it started up. So I continued troubleshooting the matrix.

The not booting became more common as I was removing and installing the MPU board so I had to get to root of that, eventually I found the culprit to be U8 having a shoddy connection, I could take it from not booting to booting just tapping on the memory chip. I decided to take it out and attempt to clean it up and the machine totally lost it's brain. Then I took it out again for a deeper cleaning and suddenly the entire machine started working, all the switches were fine and everything popped into place.

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