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12542Re: [midatlanticretro] Testing a TIP120 transistor

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  • Mr Ian Primus
    May 9, 2009
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      --- On Sat, 5/9/09, Joe Giliberti <Starbase89@...> wrote:

      > One of my pinball machines (that was built it 1977 and uses
      > a Motorola
      > 6800-based computer for scoring, solenoids, etc, which (I
      > think) makes this
      > post on topic) broke down earlier today. I have reason to
      > suspect a bad
      > solenoid driver transistor, which are TIP120s. There're
      > about 20 of them on
      > the board, and I don't want to replace them all. Is
      > there a means of testing
      > them? I have a DMM and scope available.

      You can check them with the meter to see if they are shorted, but it's really more of a symptom/diagnose process. It would be silly to even think of replacing all of them. Each transistor controls a specific solenoid - and everything is well documented in the manual for the machine. Failing that, you can match up the wire colors, and follow the trace on the board to the associated driver transistor. For troubleshooting, you can simply substitute the transistor from one position that you know works into the faulty position.

      What broke on it?

      -Ian
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