(Topic ID: 230242)

Should Alltek-driven coil line be reading 20 VAC always?

By swampwiz

5 years ago



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  • 5 posts
  • 3 Pinsiders participating
  • Latest reply 5 years ago by swampwiz
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    #1 5 years ago

    On my Bally Strikes & Spares, I have an Alltek Solenoid Driver board with a few coils that are not working. For one of them (the "extra chime", which I have already excised since it was not the proper coil), I get a constant reading of 20 VAC. I took the reading for another coil that does work, and it showed 0 V until being actuated in the test, at which time it jumped temporarily, as it should. The other chimes work fine.

    As for the indicators on the board, I only get Q19, which goes to the coin lockout (which has been excised, and which is on different lines than the chimes).

    Could this be the result of a dirty pin connector?

    #2 5 years ago

    AC must be measured 'across' a winding, usually a transformer winding or an extension of that. You rarely measure to ground when measuring for AC.

    Exactly where are you placing the probes to get this AC reading?

    #3 5 years ago

    The coils in this machine are DC and you'd expect to see ~40VDC present at the coil at all times when measured to ground (the ground strap in the cabinet is a good place to test too). The SDB completes a path to ground for the coils when they fire.

    The AC voltage at this coil is concerning. Check the voltage at the rectifier board. With your DMM on VAC put the black lead on E8. This is one of the connection points for the transformer. Put the red lead on TP4. You should have ~7.3VAC. If this is right then test the other TPs with black on ground. If they are fine then test the diode on the coil in question with the machine off. If it is OK then maybe the 20VAC on the coil was a misreading due to the coil firing.

    Here is a link to the manual if you don't have one https://www.ipdb.org/files/2406/Bally_1978_Strikes_and_Spares_Manual_w_Schematics.pdf

    #4 5 years ago
    Quoted from Homepin:

    AC must be measured 'across' a winding, usually a transformer winding or an extension of that. You rarely measure to ground when measuring for AC.
    Exactly where are you placing the probes to get this AC reading?

    I am placing them on the 2 wires leading to the coil themselves (the coil has been excised already).

    #5 5 years ago
    Quoted from Cheddar:

    The coils in this machine are DC and you'd expect to see ~40VDC present at the coil at all times when measured to ground (the ground strap in the cabinet is a good place to test too). The SDB completes a path to ground for the coils when they fire.
    The AC voltage at this coil is concerning. Check the voltage at the rectifier board. With your DMM on VAC put the black lead on E8. This is one of the connection points for the transformer. Put the red lead on TP4. You should have ~7.3VAC. If this is right then test the other TPs with black on ground. If they are fine then test the diode on the coil in question with the machine off. If it is OK then maybe the 20VAC on the coil was a misreading due to the coil firing.
    Here is a link to the manual if you don't have one https://www.ipdb.org/files/2406/Bally_1978_Strikes_and_Spares_Manual_w_Schematics.pdf

    The other coils show no AC voltage when not actuated, so there is not a problem with the voltage coming from the power board. There are only 3 coil lines that don't show the proper behavior - this one, and 2 others that just show 0 V always.

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