(Topic ID: 325332)

Power box thermistor can fail?

By AlexRogan84

1 year ago


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  • Latest reply 1 year ago by phishrace
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    #1 1 year ago

    My question stems from a Theatre of Magic

    Game is great yet it powers on with a screech. Really loud one and sometimes a quieter one when it turns off.

    I would describe it like a power surge but not from the power in the house, more like as the power comes into the game it is coming too fast or too strong. I’m no electrical engineer so not sure those terms even apply.

    Reading online, the power box has a thermistor they call it in series with the black power wire. The purpose is apparently to limit this power surge at start-up.

    Given my power on screech noise, I wondered if perhaps this component has failed? Or can they even fail?

    I have my power box opened up and I can see clearly all the connections for the power switch, fuse, thermistor and a couple additional multi wire connectors. Nothing looks frayed or crispy.

    Is there a way to test this thermistor or otherwise confirm everything is good in there?

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    #2 1 year ago

    You'd know if it failed. It would be burned up.

    LTG : )

    #3 1 year ago
    Quoted from LTG:

    You'd know if it failed. It would be burned up.
    LTG : )

    And I take it they either work or they don’t? But nothing in between like they “sorta” work?

    #4 1 year ago
    Quoted from AlexRogan84:

    And I take it they either work or they don’t?

    Anything else would be rare.

    You could lift one leg and try the game briefly. I would leave it or a new one off for long.

    LTG : )

    #5 1 year ago

    Yeah, they generally explode when they fail ha. You'd notice for sure...ask me how I know...

    #6 1 year ago
    Quoted from grantopia:

    Yeah, they generally explode when they fail ha. You'd notice for sure...ask me how I know...

    Haha I can only imagine! Hard to get that magic smoke back in once it gets out

    I’ll make sure everything is snug and reassemble the power box. I am also looking closer at the grounding wires and connections to make sure they are all decent. I know bad grounds on old cars makes for weird things to happen and I think that applies to pinball machines too.

    #7 1 year ago

    They can fail without exploding. The symptom is the game won't boot for minutes when cold. Turn on power switch, no power to the backbox or anything else. Easy to test using a jumper around it.

    I don't suspect your screech is coming from the thermistor, but as mentioned, you can jumper around it to test. Be careful as it all 120 volts. Make sure jumper is at least 18 gauge wire and has good alligator clips.

    If you haven't already, I would suggest reseating all 4 ends of the ribbon cable that connects to the sound board.

    #8 1 year ago
    Quoted from phishrace:

    They can fail without exploding. The symptom is the game won't boot for minutes when cold. Turn on power switch, no power to the backbox or anything else. Easy to test using a jumper around it.
    I don't suspect your screech is coming from the thermistor, but as mentioned, you can jumper around it to test. Be careful as it all 120 volts. Make sure jumper is at least 18 gauge wire and has good alligator clips.
    If you haven't already, I would suggest reseating all 4 ends of the ribbon cable that connects to the sound board.

    Thanks. I definitely don't see any trouble booting up when cold. Or hot. Or any other time. It just makes the loud screech and then is ready to rock n roll.

    I'm in agreement with you about the sound board possibility. I just the other day got a replacement ribbon set and put all new ones in. It didn't change anything though. Doesn't mean it isn't still related to that I guess. Might be one or more pins on the board going to those ribbon cable connectors that isn't quite right.

    I think what I'm going to do is disconnect one speaker at a time and see what I find or hear. When I turned the game off earlier today, I was listening more closely and it seemed like the noise was more towards the left speaker in the backbox than elsehwere, so that's where I'll start.

    #9 1 year ago

    A question for the Bally gurus: Is there a mute line somewhere on one of the boards that should prevent this during power up?

    #10 1 year ago

    The best way to find faults before touching anything is to use your meter and measure all test points to confirm all voltages are withn specifications.

    If you don't do this you are just guessing and are likely to wander off in all sorts of dead end directions.

    #11 1 year ago
    Quoted from pins4u:

    The best way to find faults before touching anything is to use your meter and measure all test points to confirm all voltages are withn specifications.
    If you don't do this you are just guessing and are likely to wander off in all sorts of dead end directions.

    Is there an expected voltages “map” or guideline that I can use to do this? I like the idea and suggestion and agree you’re right about first things first.

    #14 1 year ago
    Quoted from pins4u:

    Detailed power info here.

    Pin wiki doesn't list sound board voltages. I don't suspect power is a problem, but the schematics section of the manual shows expected voltage for each pin on sound board. Requires 5V DC and 18V AC. Sound board doesn't have test points, so voltages need to be checked at the connector.

    #15 1 year ago
    Quoted from Atari_Daze:

    Yep they can and do "fail" but that's kinda their job.

    That's a varistor. Does the same job as a thermistor, but different device that's wired differently. Definitely don't want to switch a varistor for a thermistor and vice versa.

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