Pinball Machine -Fuse

Discussion in 'The Projects Forum' started by Dalaran, Feb 7, 2010.

  1. Dalaran

    Thread Starter Active Member

    Dec 3, 2009
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    So I've finally found some time to get a chance to work on a vintage pinball machine I've had in collection for awhile since the driver board has reached my front door. Whenever the switch is flipped the main fuse is blown (the first fuse from the wall). Nothing is really connected except for the power supply board so I figure it must be a hard short somewhere.

    The main transformer in the head is labelled 1-8 on the input side. The schematic shows coils between 1-2, 3-4, 5-6, 7-8. Measuring the resistance across all of these gives me an 'open circuit' reading for 1-2, 5-6, 7-8, and only ~1ohm across 3-4. Do I have a short in my transformer causing this, or is this normal in some cases? Could be a nasty fix. Thanks.
     
  2. cumesoftware

    Senior Member

    Apr 27, 2007
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    Please, could you post a photo of the transformer, so we can see how the coils are arranged?
     
  3. Dalaran

    Thread Starter Active Member

    Dec 3, 2009
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    Attached, and next on the schematic. Please let me know if you need clarification on anything, I know the pics aren't the best.
     
  4. Dalaran

    Thread Starter Active Member

    Dec 3, 2009
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    schematic attached
     
  5. cumesoftware

    Senior Member

    Apr 27, 2007
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    Your coil 3-4 must be shorted. The other coils should not be open, contrary to what you said, but they should have a relatively big DC resistance. I thing you are using the wrong scale to measure the resistance. If all the other coils were actually open, the fuse wouldn't blew even if there was a short on the remaining coil.

    Could you measure the resistance again? Are you measuring with the transformer completely disconnected?
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    You wrote:
    Is it possible to disconnect the transformer from the rest of the power supply?

    In really old power supplies, the electrolytic capacitors are likely to be bad. If you see ruptured capacitors, that's a sure sign that they're gone - but even if they are intact, they may be shorted internally. This would cause a heavy load on the transformer's secondary, which would quickly blow the fuse on the primary side.
     
  7. Dalaran

    Thread Starter Active Member

    Dec 3, 2009
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    I have disconnected everything from the secondary of the transformer. This includes the 2 bridge rectifiers for the lamps and solenoids, the fuse for the display power and all the connectors going to the power supply board. The fuse is still blowing and I am still getting the inconsistent readings on the DMM. By that I mean resistance between pins 3&4 is ~1ohm while 1&2, 5&6, 7&8 are all too high for the multimeter (I will remeasure these asap).

    Leads me to believe it must be the transformer. Is it possible to repair, or must I start sourcing a new one?

    Cheers.
     
  8. Dalaran

    Thread Starter Active Member

    Dec 3, 2009
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    Thanks for the help. I have completed disconnected the transformer. My first measurements it seems I was not getting good contact due to corrosion on the leads. After re measuring I am now seeing less that 1ohm on each of windings 1&2, 3&4, 5&6, 7&8. Is this normal or is this resistance much to small indicating they are all shorted?!

    Thanks.
     
  9. cumesoftware

    Senior Member

    Apr 27, 2007
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    This is not normal. Those primary windings should have well more than 1Ohm DC resistance. For instance, the primary of the transformer inside my 30V 5A PSU has 9 to 10 Ohm DC resistance. And that is a 330VA input rated PSU! What confuses me most is that all the windings seem to be shorted.
     
  10. Dalaran

    Thread Starter Active Member

    Dec 3, 2009
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    Thanks for the reply. I found a transformer on my brothers work bench that he said worked, I measured the primary of it which was ~10ohms as well.

    It to confuses me why they would all be shorted... but I have rechecked and my measurements stand of ~1ohm across each winding.

    So this is definitely why I am consistently blowing fuses then. Now a fun fix heh, thanks for the help. Any other input appreciated.

    Cheers.
     
  11. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
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    Does the fuse blow when you pull the 6J1 plug? I don't see on the schematic what's to the left of the power switch.
     
  12. Dalaran

    Thread Starter Active Member

    Dec 3, 2009
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    No the fuse does not blow when the primary of the transformer is disconnected. The only things before the transformer is the fuse, then the AC line filter and a switch. I have unbolted the transformer and there doesn't seem to be anything shorting it out against the casing or anything, all of the secondary wires are disconnected, and it is the only thing connected with that 6J1 plug.

    Looks like I will be sourcing one. Thanks all for the help.
     
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