(Topic ID: 290458)

Bally AS-2518-22 Voltage regulator problem with high voltage

By Inkochnito

8 months ago


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  • 78 posts
  • 14 Pinsiders participating
  • Latest reply 7 months ago by Inkochnito
  • Topic is favorited by 4 Pinsiders

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    #17 8 months ago

    Are you sure about the 95V and 98V at the Q22 pins? The voltage on the base should be higher than the emitter, not lower.

    SDB_HV1.png

    1 week later
    #30 8 months ago
    Quoted from Inkochnito:

    When you measure the totall resistance of R54, RT1, R56 theoreticly you should be getting something around 115-120K.
    When measured on the good board it starts around 1M and goes down slowly (due to the cap).
    When measured on the bad board it goes rightaway to 115-120K.

    On the bench and disconnected from anything, when I measure it on a good board from the ground side of R56 to TP2 side of R54, I get 115k ohms immediately even after swapping the meter leads around. There's no capacitance across that resistor ladder and it goes against the reading of your "good" board.

    Quoted from Inkochnito:

    For example R56.
    This is a 82K resistor, but when measured in circuit it will start at 1M and slowly drop down (on the good board).
    When measured on the bad board to goes to 82K rightaway.

    My working board measures 82k ohms across R56 immediately even when swapping the meter leads around.

    All resistors measure to spec right away on my board other than R35 but that's because it has the C26 filter capacitor across it.

    Is resistor R51 (22k ohm) on the bad board original and still good? You've got 175 volts across it. That's 1.4 watts of power dissipated by a 0.5 watt rated resistor.. She should be burning if she hasn't already gone open circuit.
    Measure the long distance resistance across R51 from the collector of Q23 to the collector of Q21 in case there's a connection/trace issue to that resistor.

    #33 7 months ago
    Quoted from G-P-E:

    Your 'good' board appears to have either a bad resistor R35 or a bad connection to it. R35's job is to drain current from C26 after you shut the machine off. Your measurements are showing that the cap is still charged.

    It's been more than 6 months that I've worked on one of these boards but my rusty memory tells me it takes about a minute to pretty much discharge C26.

    1 week later
    #38 7 months ago
    Quoted from Inkochnito:

    This time I had succes!

    Good to hear. So you got yet another source of 2N3440 transistors since yesterday and they worked ok?

    Quoted from Inkochnito:

    I must say I do not trust those cheap Chinese transistors.

    Can you tell us all the Chinese vendors (with web links) you got the working and non-working transistors from?

    #43 7 months ago
    Quoted from Inkochnito:

    The source I got them from is in post #11.

    These 2N3440 from Poland might be a better source closer to you and look like good value:
    ebay.com link: 20pcs 2N3440 PNP 350V 20mA 1W TO39

    #52 7 months ago

    The question is why do we see the HV circuit blow out more than we should?

    The only time I've had to re-repair a board was when a friend disconnected/connected a display live and it killed the HV section.

    I guess another reason is when the 100k 1/4W resistors in the digit drive circuit on the displays go up in flames.

    From Dolly Parton onwards, Bally revised the high voltage F2 fuse on the rectifier board from a slow blow to a fast blow (same 750mA rating).

    #65 7 months ago
    Quoted from barakandl:

    I am sure you can have human error accidents too.

    Yes, I also had someone call today who accidentally swapped a display with the power on and blew the SDB's high voltage circuit.

    Quoted from barakandl:

    This can happen too. High voltage is a bitch.

    Not as bad as yours but those 100k resistors can go out in a blaze of glory.

    IMG_0017a.jpg

    #74 7 months ago
    Quoted from barakandl:

    I have seen the MPU board 1K2 series resistors burnt to a crisp too.

    Wow, haven't seen that.

    Quoted from G-P-E:

    Quench -- second photo, did it actually burn a hole through a 'ceramic' capacitor?

    Nope
    That's the capacitors internal disk that's uncovered.

    Quoted from G-P-E:

    The idea behind this was good but it was a poor part choice for Q24.

    I think about a year ago you mentioned a MPSA42 transistor (same as used on the display boards) was a better choice for Q24 (Vceo of 300V)? apposed to the factory used 2N3904 which is only 60V spec.

    First time I'd seen one of these particular H.V capacitors (red epoxy on the positive side). It measures good with my ESR tester but was causing the 750mA H.V F2 fuse on the rectifier board to blow every time I powered on. One for the memory bank.

    IMG_0023b.jpg

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