• Bally MPU Reset Circuit

    From John McRae@jfbmcrae@gmail.com to rec.games.pinball on Tuesday, November 08, 2022 11:14:32
    From Newsgroup: rec.games.pinball

    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
    --- Synchronet 3.19a-Win32 NewsLink 1.113
  • From Kerry Imming@kcimming@pobox.com to rec.games.pinball on Thursday, November 10, 2022 06:50:08
    From Newsgroup: rec.games.pinball

    On 11/8/2022 1:14 PM, John McRae wrote:
    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

    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
    --- Synchronet 3.19a-Win32 NewsLink 1.113
  • From John McRae@jfbmcrae@gmail.com to rec.games.pinball on Friday, November 11, 2022 07:06:17
    From Newsgroup: rec.games.pinball

    On Thursday, November 10, 2022 at 7:50:17 AM UTC-5, Kerry Imming wrote:
    On 11/8/2022 1:14 PM, John McRae wrote:
    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
    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
    Thanks Kerry - will check this weekend and get back on result.
    --- Synchronet 3.19a-Win32 NewsLink 1.113
  • From John McRae@jfbmcrae@gmail.com to rec.games.pinball on Tuesday, November 15, 2022 08:05:44
    From Newsgroup: rec.games.pinball

    On Friday, November 11, 2022 at 10:06:21 AM UTC-5, John McRae wrote:
    On Thursday, November 10, 2022 at 7:50:17 AM UTC-5, Kerry Imming wrote:
    On 11/8/2022 1:14 PM, John McRae wrote:
    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
    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
    Thanks Kerry - will check this weekend and get back on result.
    Recommended checks tested ok and no change in status. Will put this board on the side for parts. Thanks for the assist.
    --- Synchronet 3.19a-Win32 NewsLink 1.113