Bally MPU Reset Circuit

John McRae

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Nov 8, 2022, 2:14:37 PM11/8/22

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Upgraded an acid damaged Bally MPU -17 to -35. I rebuilt the Reset Circuit and changed the jumpers as well as putting in tested IC’s where ever sockets existed. Also replaced all closed sockets.
When testing the MPU I do not get the initial flicker and LED stays lit. U9 pin 40 initially does not go high however after a minute measures 5.44V
What I’m trying to figure out is what components might delay this rise in voltage. After the rise in voltage the LED does not change from the solid on state.
Also want to mention that I used .01Uf 400v caps for C3, C13 and C80 which were originally .01Uf 50v and wondering if the higher voltage caps might be part of the issue.
Thanks in advance for any assistance

Kerry Imming

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Nov 10, 2022, 7:50:17 AM11/10/22

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The voltage on capacitors is the maximum voltage, so 400v vs 50v won't
cause your issue.

On the schematics, the top of C13 is labeled "Vaux to U8". Extra
capacitance on this trace is what I suspect is causing the issue. Have
you checked R12 and the battery?

I assume you're familiar with the information on Pinwiki.com:
https://www.pinwiki.com/wiki/index.php?title=Bally/Stern#MPU_boot_issues

- Kerry

John McRae

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Nov 11, 2022, 10:06:21 AM11/11/22

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Thanks Kerry - will check this weekend and get back on result.

John McRae

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Nov 15, 2022, 11:05:50 AM11/15/22

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Recommended checks tested ok and no change in status. Will put this board on the side for parts. Thanks for the assist.

cody chunn

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Jan 31, 2023, 11:00:17 PM1/31/23

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Man, that's probably for the best. Those -17's despise technicians. I still carry mental scars from dueling with them.

Mr Pinball

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Feb 2, 2023, 1:07:15 AM2/2/23

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John Robertson

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Feb 2, 2023, 4:45:51 PM2/2/23

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> https://mrpinballmach.scam
>

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