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Burnt PCB under relay

Discussion in 'Troubleshooting and Repair' started by spdjnky_42, Aug 23, 2017.

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  1. spdjnky_42

    spdjnky_42

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    Aug 23, 2017
    Hello all! Thank you for accepting me. I am looking to pick you more advanced builders brains for a second, if you dont mind. I dabble in just about everything. My stoves blower quit working, on the "high" setting. Stove isnt very old. Pulled the panel today. Just as suspected, the board is burnt under the relay. You can still hear the relay click when you push the button for the high setting. But the fan doesnt work. I flipped the wires around on the relays, since there is one for low and one for high. The fan seemed to pull harder when the wires were switched. Not sure I understand how the fan works. It is my understanding that if the fan is 120v, then its 120v on either setting. That would leave me to believe that the motor is wound different in each setting. Therefore if it works when I switch the wires, on the high setting, then there is no issue with the motor itself. If the relay still clicks and shows no sign of damage, should I be ok just repairing the burnt spot on the board? The copper path burnt away, but the board underneath is fine. Normally I would replace the relay as well, but I am having a hard time finding a replacement. Although, it seems something had to be at fault for the burnt board. Fluke??? Poor removal of flux before assembly? I will say there is some grease (food) that has leaked onto the connector at the other end of the harness. Possible it allowed something to short? FIgured that would show sign at the plug... TIA
     
  2. Minder

    Minder

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    Apr 24, 2015
    I just did a couple of similar repairs, one on a stove and one a top end toaster oven, both the same as you describe.
    I think the reason is just that the printed CCT is not built to take the current that the relay switches.
    I actually replaced the relays, but I suspect it was just the foil had blown, I used some dry wick, (copper wick) to re-enforce the trace and both have been working fine now for some months.
    M.
     
  3. davenn

    davenn Moderator

    13,674
    1,892
    Sep 5, 2009

    hi and welcome :)

    a pic or two of the damaged area would be really helpful so people knew what you were talking about

    sharp and well lit



    Dave
     
  4. spdjnky_42

    spdjnky_42

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    Aug 23, 2017
    Thank you. I suspect another issue may play a part in this. The squirrel cage gets heavy from grease deposit. Typically a fan with a cage would start in low first then high. This unit starts it in high first. That heavy grease covered cage would cause a pretty hefty load wouldnt it? Would I be better off switching the wires so it starts off in low first, even though it would say "high". It is powered by the same button. First push is fan on in high, second push is fan on low, third it is off again. I will try to post a pic, but I already started repairing it before, I thought Id ask for some insight on what the issue may be. Maybe I am wrong and the start load will be the same. Doing the repair with 26 awg hook up wire should be better than the copper path, shouldnt it? The path is short, I would be able to reach both connectors with it.
     
  5. Minder

    Minder

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    Apr 24, 2015
    Squirrel cage? is the the motor technology or the radial fan impeller?
    If the former, it could be a single speed motor or probably it is variable. If so it should be capable of starting in high I would think.
    Any enhanced copper conductor to replace the foil will be an improvement.
    Fans are not usually a cause of this type of problem, element circuits are the culprit in my experience?.
    M.
     
  6. spdjnky_42

    spdjnky_42

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    Aug 23, 2017
    20170823_153525.jpg
     
  7. spdjnky_42

    spdjnky_42

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    Aug 23, 2017
    20170823_153606.jpg
     
  8. Minder

    Minder

    3,020
    640
    Apr 24, 2015
    Omron relay are quite common and easy to come by, replace if possible and/or at least repair copper foil as already outlined.
    Go to step one and test!.
    M.
     
  9. spdjnky_42

    spdjnky_42

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    Aug 23, 2017
    With the info given can you find a replacement? I cannot. I have a new board here with similar omron relays (different part #) However, the new board is missing one function this stove offers. So I cannot use the new one. And it was $300, so its going back.
     
  10. Minder

    Minder

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    640
    Apr 24, 2015
    I find that Digikey and mouser have them, standard Omron G5LE SP relay with 24vdc coil.
    M.
     
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