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  1. #1
    Senior Member
    Join Date
    Dec 2004

    Default Electronics: Chock Coils on Motherboards

    What are Chock Coils for?

    To help explain what I'm talking about here's a picture of a Gigabyte motherboard showing 3 chock coils, it looks like a grey insulated, maybe magnetised? ring wrapped with copper around it.

    This isn't the motherboard I have, it's just a picture I found, I'm not even sure they're called Chock but that's what was printed on the board.

    I'm wondering what they are for, because I've accidentally burnt one out by shorting it with a PCI card that got too close to it, poorly placed chock I believe, but since the board is over 5 years old, it's hard tracking down the same board, and it's just one of those boards you don't want to give up.

    If any electronic expert can tell me the properties for them, what they do, and what you'd need to know if you wanted to replace them, if you had to buy it, that would help me understand a little about them. Where do you buy these things?

    The reason I want to know this is I'm wondering whether I can 1)remove the burnt out copper and redo a new coil around the old ring with the same gauge copper, 2) remove the chock and replace it with a chock off another motherboard that looks similar, 3) just remove the chock complete and just solder wire to each point.

    Any help would be much appreciated.



  2. #2
    Join Date
    Dec 2004

    Default Re: Electronics: Chock Coils on Motherboards

    1) Yes

    2) Yes

    3) Best not to, even though it will work you may be plagued by strange interference and noise problems, but you could try it as an interim solution.

    They are called "chokes", they offer high impedance paths to ac frequencies, the higher the frequency the greater the impedance. In other words they are used to block unwanted interference in conjunction with the low impedance path offered by the capacitors associated with them.

    The ferrite is often made to be extra "lossy" in this application.
    Last edited by zqwerty; 13-01-2007 at 09:43 PM.

  3. #3
    6146-B Billy T's Avatar
    Join Date
    Dec 2004
    Middle Earth

    Default Re: Electronics: Chock Coils on Motherboards

    Quote Originally Posted by Kame View Post
    I've accidentally burnt one out by shorting it with a PCI card that got too close to it, poorly placed chock I believe, but since the board is over 5 years old, it's hard tracking down the same board, and it's just one of those boards you don't want to give up.
    Firstly, you can buy pre-wound ferrite chokes from Jaycar Electronics, so if you can't find a similar looking coil on an old MB, take the dud in to Jaycar and do some comparisons.

    Secondly, if it burned out when you shorted it, you drew an awful lot of current through the board and depending on how close (electrically) it was to the power supply, you may have killed the board. (Closer is good, further away is bad).

    Before wasting too much time on this, I'd connect a short across the damaged choke as per your option 3, then see if the board fires up and operates. If it doesn't then you can just cut your losses and dump it. If it does work, you can go on to plan B and try to replace the choke.

    You will need good soldering skills and an appropriately sized and rated soldering iron to do this without destroying the board so be aware of the risks before you start and you won't end up disappointed. If it is soldered in to plated-through holes, or it is a multi-layer board (at that location) then unless experienced, your chances of success diminish rapidly.


    Billy 8-{)
    Some days it's not even worth chewing through my restraints!

  4. #4
    Pedant and proud of it
    Join Date
    Dec 2004

    Default Re: Electronics: Chock Coils on Motherboards

    A toroidal inductor like that is likely to be the energy storage component in an onboard switchmode power supply, perhaps for the CPU. Its inductance will be critical. It might be worth rewinding it, with the same size wire, and exactly the same number of turns. One that looks like it might have a different grade of ferrrite, and would not work. Putting a jumper across it would not be a good idea.

    But the copper winding shouldn't "burn out". Usually a semiconductor would have lost its internal smoke long before that happened. Did the copper melt? If it's just the enamel insulation coating which has gone, and the board doesn't work any more, you might have 5V or even 12V on the CPU supply pins.

  5. #5
    Senior Member
    Join Date
    Dec 2004

    Default Re: Electronics: Chock Coils on Motherboards

    Here are some things I can tell you:

    When I noticed the problem, I thought it was the graphics card, because during the POST screen weird and colourful ASCII characters appeared on the screen. Eventually I lost video signal but the computer continued to run, did not hang, lock up or freeze. I could make the speaker beep by holding a lot of keys down and caps, etc still turned on and off.

    I noticed the choke was pushed against the PCI slot which is shared/linked with the AGP, it burnt it, melting the PCI slot and revealing the contacts, it does not seem like major damage, and it's possible I could still run the motherboard with the contacts exposed, I don't use this PCI slot due to it linked with AGP.

    The choke has lost its copper colour, the ring it's coiled around had flaked, I assume this is the enamel coating peeling off it. The choke heated up so much that it unsoldered one side of the joints which has disconnected it, I believe that's the cause of losing the video signal as I haven't joined it back as I wasn't sure if it was a good idea.

    The motherboard still powers on, and seems to go through fine just there's no video signal.

    Here's the image of my board and the location of this choke, this isn't however the burnt out one, just an image I found on the net.

    It's an Abit VP6 Dual P3 Processor Motherboard and had no problems with it till this unfortunate event, definitely worth trying to get it fixed.

    Basically I want to try the least risky things first, as in the end, the board will probably be dumped if I can't get it working but I'll try looking for a replacement.

    The last thing I would want to attempt to do is replace the PCI slot, soldering the choke is easy, the PCI slot however requires a very fine tip and I'd probably have to work under a magnifying glass, if I can avoid doing this I will, I don't use the slot.

    Also, is there any type of heat resistant insulation I could possibly put around the choke, or at least between the PCI and choke and AGP and choke to avoid this type of damage happening again, I also thought about relocating the choke via wires, but I don't know how well that would go.



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