(Topic ID: 261878)

Data East DE MPU Debug - Crashing CPU


By thedefog

4 days ago



Topic Stats

  • 8 posts
  • 2 Pinsiders participating
  • Latest reply 3 days ago by vec-tor
  • No one calls this topic a favorite

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#1 4 days ago

So now that I have a proper working bench power supply, I'm able to see what this DE MPU is doing wrong.

With a game rom in socket, +5v on, PIA on-off quick, Blanking on, then blanking drops out after about 3 seconds.

With Leon's test rom in socket, on boot, I get about 2-3 relay clicks of the PIAs doing there thing, then crash, but sometimes more or less.... IRQ drops low about 3 seconds after the last click.

With no rom in socket, 2 volts on all address lines for about 3 seconds, then they all go high.

Identical behavior with another known working CPU.

Address line short? Chip selection? PIA?

#2 4 days ago

I first would check continuity on all CPU traces...
Then I would check RAM...

#3 4 days ago
Quoted from vec-tor:

I first would check continuity on all CPU traces...
Then I would check RAM...

I've swapped RAM with ramtron 1608. I also buzzed this board out about 3 times prior, so good there.

I was just curious if this partial working behavior was typical of one section, like bad 74ls244s, 245, chip selection ICs. I've repaired a similar issues, but they were less complicated to debug because they were obvious to spot.

#4 4 days ago

i replaced the cpu socket and it is more consistent now, but still hangs...Replacing ROM and RAM sockets now.

#5 4 days ago

Got Leon's test running. Isolated it down to the display PIA @ 11B. The LED pin at pin 6 there was randomly firing, and pins 2-5 are completely dead on it. Could be more involved, but starting here as it is the most likely cause since the decoder & led lines are isolated.

#6 4 days ago
Quoted from thedefog:

Got Leon's test running. Isolated it down to the display PIA @ 11B. The LED pin at pin 6 there was randomly firing, and pins 2-5 are completely dead on it. Could be more involved, but starting here as it is the most likely cause since the decoder & led lines are isolated.

I was reading up on the test chip you are using...
If everything else is good you could have a flaky PIA/PIAs.
I had to replace three PIAs on a Data East Simpsons pinball
one time to get it to work... They were used to drive the
display circuity... some tech shorted the display and...BOOM.

#7 3 days ago
Quoted from vec-tor:

I was reading up on the test chip you are using...
If everything else is good you could have a flaky PIA/PIAs.
I had to replace three PIAs on a Data East Simpsons pinball
one time to get it to work... They were used to drive the
display circuity... some tech shorted the display and...BOOM.

I got lucky this time and it was just a bad RAM socket, which has been the case historically for me with any intermittent issues like this (bad sockets). Thanks for the input.

#8 3 days ago
Quoted from thedefog:

I got lucky this time and it was just a bad RAM socket, which has been the case historically for me with any intermittent issues like this (bad sockets). Thanks for the input.

Excellent!

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