Dolly – Bally MPU U8 progress

With the help of my friends at GAPAS I was able to determine test points and continuity areas of my Bally MPU for the Dolly Parton pin so that I’ll be able to put in jumpers where necessary to resolve the problems with U8.

However, while testing I found that pin 8 and pin 22 were showing continuity. I was pretty sure this shouldn’t be the case, but as I have only this Bally pinball machine – I have no other MPU to test against.

Today I was able to get my friend Robby to help me – as he has a few.  He verified that there should not be continuity between 8 and 22 as I suspected.  But then there is the issue with – well why are they connecting when they shouldn’t.

I knew that pin 8 was supposed to be connected to ground for the power portion of the circuit.  And it looked like 22 should have been to a positive power source – and after checking pin22 did seem to test good to the little through hole solder junction on the board (with a + sign next to it).  Of course this wasn’t foolproof as I was testing continuity between that + and ground… which is a big obvious NO NO.

After having stared at the board so long while determining the pin out connections – I was thinking perhaps it was a bad capacitor.  C13 seemed to stand out to me – it is near the battery, and could have been damaged some way from the acid problem.  Or, perhaps, it was due to heat or some other from when removing the IC stand at U8.

I cut a lead off the capacitor – and like magic no more continuity between + and -.  Now, I’ve added a new 0.0uF Axial Ceramic capacitor to my shopping list for this week at the electronics component store..

Hooray for progress, and thanks again Robby.

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One Response to Dolly – Bally MPU U8 progress

  1. avannoy says:

    Progress is a good thing! Congratulations!

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