Is there likely a way to repair a blown PWM output?



  • Setting up berdair motor and the example image for flyback diode I first found on google had the anode and cathode around the wrong way 😕 meaning there was a full short on the PWM output (it turned it off pretty quickly, but not quick enough.

    Is there likelyhood the component that blew will be user replaceable? (none of the chips smell like the magic ingredient came out (smoke).

    I have soldered surface mount stuff with a soldering iron before (modded a few playstation and xboxes for friends many moons ago).

    I did get it working on PWM1 output, but would just like to fix it if possible.



  • Easy enough to fix with care. Hot air rework station would be the best way, however you can use a soldering iron with patience. I replaced the entire micro on my board, a 3 pin FET is just a walk in the park. I guess years of experience helps. Flux is key to soldering the part back correctly, Some really good stuff on YouTube for this, and sadly some bad stuff to.

    Jeff


  • administrators

    The tricky part is removing the blown MOSFET. It's easy with a hot air rework station, difficult otherwise. Soldering the replacement MOSFET can be done using an ordinary soldering iron with a fine tipped bit.



  • I do have soldering station with hot air luckily, whether or not I can get the SMD MOSFET locally or have to order online is the question.

    Online it seems..

    @dc42 can you please confirm this is a suitable replacement?
    http://au.element14.com/nxp/pmv40un2/mosfet-n-ch-30v-4-4a-sot-23-3/dp/2469654

    And how I can confirm if thats the part that would have blown?


  • administrators

    The part is a PMV40UN2 so that's spot on.



  • Good you have the hot air rework station, personally I don't even attempt to do SMD work without. I prefer about a 1mm wide chisel tip. Too pointy and they do nothing good. Flux flux flux. Clean up with some 91% + iso and all is well.

    Also learning the art of drag soldering is always a good skill, not useful in this case but sure comes in handy.

    Jeff



  • Ohh, a bit of kapton tape covering areas you don't want melting is a useful trick. If you have plastic connectors too close for example, cover them loosely with kapton. More or less make a heat shield.



  • Good thing it happened to Brian and not to me. My thick fingers would have a great deal of trouble over this. Besides, all I have is a small soldering iron. He is the electronics I am mechanical. Good split.



  • So, what is the correct orientation for the flyback diode? I'm getting ready to connect a Berd-Air also and the orientation discrepancies have me nervous. I would rather not get lucky…

    It would be great if the Wiki page could be updated. https://duet3d.com/wiki/Connecting_and_configuring_fans

    Thanks!


  • administrators

    The wiki page already mentioned the need for a flyback diode, but I've just updated the text with information about the polarity.



  • If you have a microscope, it would make the job a lot easier! 🙂


  • administrators

    I find a pair of strong reading glasses sufficient during soldering, supplemented by an eyeglass for inspecting the joints after soldering.



  • @ShadowX:

    If you have a microscope, it would make the job a lot easier! 🙂

    I find that to be too much mag in most cases. Great for final inspection however.


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