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common mode choke

Discussion in 'Troubleshooting and Repair' started by BobWells, Nov 17, 2018.

  1. BobWells

    BobWells

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    Nov 17, 2018
    Hi all, I have a bass amplifier I want to repair, the problem is the switch mode PSU, one of the inductors has a break in the winding, the inductor is on the AC side of the PSU.
    Ive put a blob of solder on the break and it now works, but I would rather replace it, problem is, I can find one of the correct value anywhere, I've measured it at 12mH, and the circuit is protected by a 5A fuse.
    I've found a 10mH @ 5A, question is will this do the job.
    Thanks in advance, BobWells
     
  2. kellys_eye

    kellys_eye

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    Jun 25, 2010
    Short answer - probably.

    Long answer - show us the schematic or tell us the make/model of the amplifier.
     
  3. BobWells

    BobWells

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    Nov 17, 2018
    Hi Kellys-eye, thanks for the reply, there are no schematics available, but the amp is a TC Electronic BG250 bass amp. The choke is on the AC side of the rectifier, if that helps.
    The mains in goes positive through the 5A fuse then to a thermistor, then to the choke, the choke has two windings, one takes positive the other negative.
    Hope this helps.
    BobWells
     
  4. kellys_eye

    kellys_eye

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    Jun 25, 2010
    The common mode choke is made to carry the operating current (and then some) so have you checked WHY it's become open-circuit? They don't do so for no reason!

    The device is used to prevent EMF (interference) and the equipment will work without it if you have to (bypass it completely) although this would be recommended only as a temporary solution to prove the rest of the equipment is ok.

    I suspect you may have a shorted switching component (MOSFET) - did the mains fuse blow as well?
     
  5. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    Can you show us a picture of the choke please?
    Thanks
    Adam
     
  6. BobWells

    BobWells

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    Nov 17, 2018
    Hi, here's a photo of the choke, the corner nearest the camera is the one that is broken
     

    Attached Files:

  7. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
  8. BobWells

    BobWells

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    Nov 17, 2018
  9. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    Or you could re-wind it with the correct size of enamel wire? Just mark the start and end point with a permanent marker pen and count the number of turns. It will be near enough.
    Adam
     
  10. BobWells

    BobWells

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    Nov 17, 2018
    oK Adam, I might give that a try, thanks very much for your input, Bob
     
  11. kellys_eye

    kellys_eye

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    Jun 25, 2010
    Is that a picture of the choke in its 'repaired' state? If so I see nothing wrong with it at all and looks safe to be reused as-is.
     
    Arouse1973 and duke37 like this.
  12. duke37

    duke37

    5,189
    704
    Jan 9, 2011
    You should be able to find the break in a fat wire like that and repair it.
    I do not see any signs of heating. Are the circuit board tracks continuous?
     
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