(Topic ID: 197745)

So... how much damage did I do? +-12VDC (CN2 Whitestar)

By OHMI_Arcade

2 years ago

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  • 6 posts
  • 3 Pinsiders participating
  • Latest reply 2 years ago by OHMI_Arcade
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    audio power 12V reverse.jpg

    #1 2 years ago

    Suppose you accidentally switched the +12VDC and the -12VDC on CN2 of a Whitestar CPU/SOUND Board (SST) and now the sound is loud and distorted with a high amount of hum. What do I start replacing? I think I might need to replace U26... does the fact that the speaker still makes noise mean that it might have survived? Anything else likely blown?

    Thanks... one of those days where I shouldn't have even tried working on my pins. Ugh!

    #2 2 years ago

    You may be lucky. Start with the two amps. You can use diode test on them to compare to good amps.
    Chris Hibler - CARGPB #31
    http://www.PinWiki.com - The new place for pinball repair info

    #3 2 years ago

    How did this happen?
    Were you repinning?
    Chris Hibler - CARGPB #31
    http://www.PinWiki.com - The new place for pinball repair info

    #4 2 years ago

    How'd this happen? Well, the more I played the SST the more I thought the sound issues I've been having might be caused by noise on the 5vdc. Specifically, I noticed some display freezes and resets along with the sound issues.

    So... I thought I'd hack in an external power supply to see if it improved things. That's when I screwed up the 12vdc polarity. Crap!

    #5 2 years ago

    Diode 102-105 are conducting when + and - 12Volt is reversed.
    In example below it results in a short between between -12Volt to +12Volt through Diode D104 and D105

    When the powersupply shuts off only one 12V rail (due to overload) , the speaker is continuous powered by 12Volt (+ or -) relative to GND. Also capacitors C116 or 119 is wrong polarized this way.

    audio power 12V reverse.jpg

    I think that the opamps are relative safe behind the 7x05 regulators.

    It's a little guess what really happened and whether or not the (+) and (-) 12Volt stayed active all the time.
    Inspect capacitors C116,119,109,112 and diode D102-105.

    #6 2 years ago

    Thanks for the detailed write up zaza !

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