(Topic ID: 233814)

Bally -22 HV HELP

By Fordiesel69

5 months ago

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  • 11 posts
  • 5 Pinsiders participating
  • Latest reply 4 months ago by Fordiesel69
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    hvnew (resized).jpg

    #1 5 months ago

    Installed a whole kit but it had the bux85g in it. Worked for 2-3 minutes now I can only get 8vdc out of the HV section. Any ideas what to check?

    Attached is a photo if you want to check my work. I did use mica and a new plastic screw thru the bux 85g.

    The original HV section did not work, it just fed the full 230v to the displays thus ruining all of them. It was visually perfect however, no burn.

    hvnew (resized).jpg
    #2 5 months ago

    You have the collector connection to the transistor cut off (middle leg) which is what is needed to be done here. But with the collector pin cut, the only means of connecting the collector is through the tab. But you used an electrical insulating thermal gasket there (thermal gasket is OK) and you also used a nylon screw which is not OK. You must use a metal screw there with a star lock washer on bottom of board so the transistor can make good electrical connection with the trace on the bottom of the board.

    #3 5 months ago

    Really the instructions I read about the bux84 conversion wanted the screw shrink wrapped and a nylon washer used. I will swap out with metal screw and see what happens.

    #4 5 months ago

    TO-66 transistors (old 2N3584) relies on the case to make the input connection. You get the same connection through the tab of the new BUX85.

    You *could* isolate the tab from the heatsink but still must make good connection to the trace that shares the same screw hole. To do this, you need to reduce the screw size to a #4 and use something like a 7721-7PPSG nylon shoulder washer. This would be an ideal condition as the heatsink would no longer be connected to high voltage (original design had the heatsink connected to high voltage) but still make connection to the PC board.

    See this thread:

    #5 5 months ago

    R51 is getting HOT. I went ahead an changed the screw to ensure continuty. No dice. Still 8v. I think the two 2n3440 are toast as in diode test they do not match my working boards. I wonder if the BUX85 is toast as a result of it not being grounded.

    #6 5 months ago

    Would my plastic screw have caused things to fail?

    #7 5 months ago

    Not likely. Hot R51 is due to Q23 being fully turned on. Missing collector connection to Q22 (plastic screw) would result in Q23 being fully turned off and R51 would remain cool.
    Sounds like Q23 is shorted. Q22 probably isn't too healthy either.

    #8 5 months ago

    If you replaced Q22 and 23 and they blew in a few minutes, you may have gotten some bad(counterfeit)transistors. Where did you get "kit"?

    #9 5 months ago

    Anytime i see a burnt / over heating R51 pretty much know the HV section transistors are shorted. Pretty good tell you can pick up at a glance.

    too bad 2n3440 goes EBC otherwise it would be safer / easier to use soemthing like MJE3439 or TIP50. Put one of those small TO-220 heat sinks on Q23 but it would be flapping around. I guess you could drill a hole or do some kind of fold over mounting to the right.

    Maybe Q22/Q23 failed because because the bux85 collector was floating? Not sure....

    #10 4 months ago

    It's always best to replace all 3 of those transistors at once. Otherwise you may chase your tail but eventually the merry go-round will stop, and it will work fine. I don't like revisiting problematic high voltage sections, so out with the bad and in with Great Plains good stuff. New filter cap, pot and whatever else looks or measures tired.

    #11 4 months ago


    Got the kit from a very well known supplier. I changed VR1, Q22 and Q23 again from parts from marco to make sure they are from a different source. Perfect. Got the voltage down to 160 and all is well.

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