Pinball machine +12V measuring 28V

Discussion in 'General Electronics Chat' started by AWEInCA, Jun 11, 2009.

  1. AWEInCA

    Thread Starter New Member

    Jun 11, 2009
    Hi have been searching for an answer to my problem all over the NET. I hope it is ok if I ask it here.

    I've been helping a friend with his Jurassic Park pinball. It all
    started with the F1 fuse constantly blowing on the power supply

    1st: I replaced both BridgeRectifiers BR1 and BR2

    2nd: The Power Supply contained all fast blow fuses so I replaced them
    with Slow Blow Fuses.

    Then the sound board completely fried. (I think it was because of the
    slow blow fueses. High power getting to sound board for a longer
    period of time)

    3rd: I replaced the Power supply board with a Rottendog board DPS004.

    I decided to measure the power on the board and that is when I
    discovered the +12V is actually 24.8V. All other voltages are fine. I
    don't think the power supply board is the problem since this one is

    What do I look at next?

    I realize this question is specific but I am looking for other general places to look for the problem. I don't believe it's any of the PCB boards.

    Should I replace the transformer?

    I would really appreciate any ideas/help/info you can give,
  2. pfofit

    Active Member

    Nov 29, 2006
    The schematic can be found here. and board image board image

    There are two 12 volts on this board, regulated 12V and unregulated 12VU. If the regulated is 25V then the board has been toasted.

    If it's the unregulated 12 volts then the Ac voltage is wrong by double (if your measuring it correctly) and depending on how long you have had it powered like that then it still may be toasted due to a probable overvoltage on the bridge output caps rated at probably 16 volts.
    Also depending on how the regulators held up, then the main boards may be damaged.

    If the 12V unregulated is double, it may be that the transformer is 110/220 volt switchable and someone has buggered it up.

    I would check the AC input voltage on pins 9,10,11 on connector CN1X12 first and not power up that board with the output connectors connected until you verify that the Ac is correct or your measuring techniques are correct.

    As well, there are multiple test points for varying dc voltages. What are their values. Again with the output connector disconnected.

    Last edited: Jun 11, 2009