(Topic ID: 306342)

Low Transformer Voltage Output?

By Nchezey_5916

2 years ago



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    #1 2 years ago

    I am very new to the world of pinball restoration and wiring/electrical systems were never my strong suit while working on cars so this may be a dumb question but…. What is considered too low for voltage output when working with transformers?

    I’m currently restoring a Gottlieb System 1 and started by testing all of my wiring/voltages to make sure things are up to par. When I got to the transformers I found that several of the readings I’m getting are well below the spec in the schematic. I had a few that were only slightly off and I wasn’t too concerned with those but I started getting several that seem pretty low to me.

    I attached a picture of the schematic with my recorded voltages written next to each wire. I’m mainly concerned with the two that are supposed to be 69v and read out at 16.5v, but I think that most of the ones on the bottom of the picture are pretty low as well.

    Thoughts?

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    #2 2 years ago

    You're measuring your voltages wrong. On the 25V AC circuit, you measured 18V on one leg and 16V on the other. You should be measuring across both legs for a single reading.

    Transformers rarely go bad. Better to test incoming and outgoing voltages at the power supply board.

    http://www.pinrepair.com/sys1/index.htm#power

    #3 2 years ago

    Have you checked how the transformer primary is wired? That transformer has taps for 100, 115, or 130V connection. You should wire it to most closely match your incoming voltage. If for instance you have your primary connected for 115V but your incoming is actually 105V, then you would expect the outputs (secondaries) will be below the voltages shown on your schematic.

    #4 2 years ago
    Quoted from phishrace:

    You're measuring your voltages wrong. On the 25V AC circuit, you measured 18V on one leg and 16V on the other. You should be measuring across both legs for a single reading.
    Transformers rarely go bad. Better to test incoming and outgoing voltages at the power supply board.
    http://www.pinrepair.com/sys1/index.htm#power

    This is exactly the kind of thing I was hoping to hear! I would much rather look like an idiot than actually have a bad transformer. I’ll have to recheck them again this afternoon and do it the right way this time!

    Am I correct in understanding that I only need to measure across both legs on the ones that show a “shared” voltage between two wires in the schematic? If this is the case then my top 4 readings were taken correctly by going to ground with my other lead, right?

    Also, the power supply board was one of the first things I checked and I wasn’t getting my -12v outgoing to the control board. Someone told me I should go back to the bottom panel and test the rest of it before anything else since I had only done the bridge rectifiers.

    #5 2 years ago
    Quoted from JethroP:

    Have you checked how the transformer primary is wired? That transformer has taps for 100, 115, or 130V connection. You should wire it to most closely match your incoming voltage. If for instance you have your primary connected for 115V but your incoming is actually 105V, then you would expect the outputs (secondaries) will be below the voltages shown on your schematic.

    It sounds like I was testing incorrectly on some of the wires so I’ll probably start by retesting them correctly and then see where I’m at.

    This is great information though! Are you referring to what I have circled in the picture below??? If so it looks like I’m wired for 115v

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    #6 2 years ago
    Quoted from Nchezey_5916:

    If this is the case then my top 4 readings were taken correctly by going to ground with my other lead, right?

    No, you measure AC one side of the transformer coil to the other side of that winding. The center tap in your transformer happens to be ground which is why it worked.

    Don't get hung up on voltages that are 'close' like if you measure 18 volts out of the 14 volt lugs - transformers are notoriously unexact (this is why there is voltage regulation later on down the line from them). It's going to vary with load and other factors.

    #7 2 years ago
    Quoted from slochar:

    No, you measure AC one side of the transformer coil to the other side of that winding. The center tap in your transformer happens to be ground which is why it worked.
    Don't get hung up on voltages that are 'close' like if you measure 18 volts out of the 14 volt lugs - transformers are notoriously unexact (this is why there is voltage regulation later on down the line from them). It's going to vary with load and other factors.

    Aaaah, ok. That makes sense I guess. And good to know! In that case, after retesting them correctly they all look to be ‘close enough’.

    Thanks for your help on this everyone!

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