Mc-60 speed controller won't work anymore

Discussion in 'The Projects Forum' started by SlickR187, Apr 26, 2016.

  1. SlickR187

    Thread Starter New Member

    Apr 24, 2016
    2
    0
    I recently got an MC – 60 speed controller and motor out of the treadmill to upgrade my drillpress to variable speed. After I pulled the parts out of the treadmill I just wanted to do a brief test before the installation on to my drillpress. I was following a video with instructions and I wired it up to test it and the first test everything went great except for I think my pot did not have enough resistance so I went to change it out with a pot with more resistance and in the process of doing so I bumped the pot into that heat sink surrounding the controller and shorted it out while trying to unplug it. It sent a good little spark and so I wired a new pot to it and tried to started up again and it would turn on for a few seconds and then turn off. Now it doesn't turn on at all not do any of yhf LEDs turn on. I tested all the LEDs and all turn on when I put voyage to them directly. I only wired the ground to it just while I was doing the test. When installed to the drill press I was going to ground it to the machine directly. Was grounding it like I did the first wrong move? Second where do I start to troubleshoot when all the components seem to look good and not burn disc colored or bulged ? The only thing that happens now is the 5w 5.6 k big white resistor just heats up and nothing else. Is it a complete loss now or can I replace some components and get it to work again?

    im a beginner so please be nice when responding.

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  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,571
    2,381
    You can earth ground the aluminum frame, but the rest of the electronics are not galvanically isolated from the AC supply so any connection to ground can blow semiconductors on the controller.
    There is previous posts here that show a reverse engineered schematic, I have a copy if you cannot find it.
    Max.
     
  3. SlickR187

    Thread Starter New Member

    Apr 24, 2016
    2
    0
    Thanks for your reply. I haven't been able to find it. As far as the semiconductors go. Do you think i should try replacing all of them?
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,571
    2,381
    Here it is, try a trouble shooting with this first.
    Max.
     
  5. IamJatinah

    Member

    Oct 22, 2014
    70
    14
    Whoa....

    Motor Controllers usually use a HOT ground!! Caution!!

    Here what that means....you have a metal frame around that board, which does attach to Earth Ground in the machine. That is "NOT" circuit ground!!!!

    When the wire came loose, the power must have been applied to make such a burn, and please remember to REMOVE all power from ALL electronics during connection/release of connections, or RISK total logic failure.
    I can explain further for those that would like to know why, but trust me, plugging and unplugging cables when there is power applied, is a great way to trash any electronic assembly, unless it is specifically listed as "Hot-Swappable".

    ** HOT GROUND ** Your MC-60 takes AC-Line and AC-Neutral in, and selectively passes power onto that dc motor, in an ugly fashion. Circuit GROUND will be at an elevated potential, meaning, that ground around that control board, is NOT equal to earth ground, and if you were to place a meter from the metal frame to the circuit ground on that PCB, you will read minimum of 60vAC and more likely near 100vAC. Therefore, when the wire hit the side of the frame, we just crossed a fluctuating ground(free riding -Hot ground) to Earth Ground, and that deals a hefty spark!

    The original potentiometer on that treadmill was electrically isolating due to the hot control circuits.

    If there wasn't power applied, there would have been little to NO spark! There are "no" storage capacitors on the MC-60, and this is a Thyristor Rectified motor control board, and is the worst design I have ever encountered from any released treadmill!

    So....with all that babble said, you have most likely ripped U1, LM324N IC, and there is another LM324 on that board that could have been taken out with the spark-path to ground. You will also want to check the TO-92 sized devices before repowering the unit.

    Good Luck!
     
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