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Broken brush-less DC motor module

Discussion in 'Troubleshooting and Repair' started by Bross, Nov 18, 2015.

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  1. Bross

    Bross

    7
    0
    Nov 17, 2015
    Hello! I have a problem with my DJ turntable. It has little torque, goes slow (with a little bit irregular speed) and needs even help to run with the finger. I isolated the problem and I know it's in the motor module (I have another working turntable that is the same and tried interchanging modules).

    I bought it already broken (very cheap, of course), thinking that it was just a broken fuse... But for some reason that I don't understand, this brand didn't include it to protect the circuit. It didn't turn on, and I suppose they plugged it to 230V in the 115V mode (in the seller's photos I saw it set at 115V here, in my 230V country). I opened the transformer with a hacksaw and found a broken 115 ºC thermal fuse. Now, for testing, I changed it with a 2A intensity fuse and turns on, but the motor doesn't respond well, as I explained before.

    It is a Numark tt500 with a brush-less DC 30V motor. As far as I know, its speed is controlled electronically and it seems that the processor controls the motor phase difference (it's a 3-phase one). Also, I found on the Internet a guy with exactly my turntable who had the same problem, so I guess that his analysis helps to find it out (but I don't understand the triangle terminals on his diagram, what are they?) He says that a phase may be lost (that's what I supposed with the irregular speed), but I'm not sure how to find if it's some transistor or some passive elements that it could be broken. Or well... maybe the motor itself, but I hope it's not! I tested the transistors with a multimeter to find if they are shorted, but there is always resistance between its connectors. And no, there isn't any component that is clearly burned, everyone says to my eyes "me? Naah, I'm like brand new, yo!") as you can see in the attached photos.

    It only works with the plate on (induction requirements, I presume!)

    No tt500 diagram on the Internet (or at least I didn't find it), just the ttx one, a newer model with similar features and some more (like a data screen), but I'm not sure if this model has the same motor (there's a web with spare parts that shows two versions of ttx, one with the same motor and other with the same as the ttx usb, an AC 24V one). I think it is the one with the same motor.

    So, my question is: what next step do you recommend? You know, if the problem is just some transistor, resistance or any cheap element, I refuse to pay for another whole motor module, even if it will takes me a lot of work... I'm not in a hurry, I'm ready to learn more about electronics if it takes that :p

    Cheers!
     

    Attached Files:

  2. Minder

    Minder

    3,102
    664
    Apr 24, 2015
    I would guess it could be one or more of the mosfets of the 6 on the heatsink if the transformer fuse blew..
    The plate you mention contains the magnets that the wound poles interact with.
    M.
     
  3. Bross

    Bross

    7
    0
    Nov 17, 2015
    Thanks! I'll get new ones and try with them then to see what happens.
     
  4. Bross

    Bross

    7
    0
    Nov 17, 2015
    There's something I didn't realize before. When I spin the motor with my hand (unplugged), I feel it a little harder than the good motor of my other turntable. I guess this means that the motor itself is broken (nevermind about the mosfets), right? Or it may work anyway?
     
  5. Alec_t

    Alec_t

    2,969
    804
    Jul 7, 2015
    Perhaps the shaft bearing needs lubrication?
     
  6. Bross

    Bross

    7
    0
    Nov 17, 2015
    Thanks for the idea! I didn't think about it... Maybe, I found lime on the lower part of the carcase and the plate is a little bit rusted (and drags the slipmat, the good one don't, maybe it's fatty).

    I'll try first with the new mosfets (I ordered all of them them through Internet, it will takes a little bit I guess) and then I'll try with some lub if I think it could be.
     
  7. bigone5500

    bigone5500

    712
    121
    Apr 9, 2014
    I would try the lubricant before replacing components. This could save you a lot of time. A cotton swab with some lube on the end can help you get into the crevices. It will also help remove any residue that would cause drag on the spindle. Also, an old soft toothbrush is great for sweeping out dust and particles.

    Good luck!
     
  8. Bross

    Bross

    7
    0
    Nov 17, 2015
    Thanx, bigone5500. I have to change, at least, one mosfet, because I detected one broken (current pass in both ways through a diode). Besides, I didn't realize that I may closed its carcass in a wrong way, because with my other turntable I had a problem (I was listening some rubbing and it has to be silent) and fixed it changing a way of a piece. I don't want to remove too much the plate, so I'll wait to my mosfets first. After that testing, I'll try to clean it if I think it's necessary (it doesn't seem to be that easy to open the whole motor and access the very axe).
     
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