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  1. #1
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
    Posts
    4,987

    Lightbulb Mill motor controller !

    Hi Guys,

    As I mentioned in another thread, the mill motor controller went bang ! Actually more of a pop-fizz and then died. The controller is a Chinese clone of a KB240 DC motor speed controller. I found enough information on line to be able to fault find this unit.

    08-07-2017-005.jpg
    This is the board in question. Looking at the power devices on the heatsink from left to right are two SCR's and three diodes. These checked out to be perfectly fine.

    08-07-2017-007.jpg
    This capacitor proved to be damaged and was replaced without curing the problem, though I did later find that the jumps in speed as the control was advanced had disappeared.

    12-07-2017-002.jpg 12-07-2017-001.JPG
    On testing I found that the motor still didn't run and that the 5 volt supply was absent. It seems that the mains input choke had gone open circuit, probably due to a dry solder joint allowing the wire to pull out of the hole that it should be secured into. re-soldering this wire brought the mill back to life. However the LED spindle speed display didn't work at all.

    12-07-2017-003.JPG
    I subsequently found that this 5 volt "78L05" voltage regulator was open circuited and was not feeding any voltage to the speed display module. Replacing it brought the display back to life.
    The mill is now back up and running, so I can get back to making the toggle clamps.

    FWIW, the total cost of this repair excluding the time it took to pull everything apart and test it was less than 50 UK pence. The capacitor cost more than the voltage regulator at 22p.
    Best Regards:
    Baron J.

  2. #2
    Join Date
    Nov 2006
    Location
    Bendigo Victoria
    Age
    77
    Posts
    7,471

    Default

    Nice save

    What mill is this controller off?

  3. #3
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
    Posts
    4,987

    Default

    Hi Fred,

    The mill is a Chinese BL20 clone, MT3 spindle, 1.5HP motor. I must admit that this mill has given me a number of problems since it was bought.

    Within the first week I discovered that the spindle was only half machined, the MT3 taper only had the top 30 mm machined in it. The supplier immediately sent a new spindle up to me. Then about four weeks later the motor burst into flames and melted. Again the supplier forwarded a replacement one. Sometime after that I managed to seize a slitting saw in a piece of aluminium plate, stripping teeth off the plastic gear. I ended up making a steel gear replacement for it. All in all I would have been better off buying a better quality product.
    Best Regards:
    Baron J.

  4. #4
    Join Date
    Nov 2006
    Location
    Bendigo Victoria
    Age
    77
    Posts
    7,471

    Default

    I used to have a little X2 and was always a bit suss about it, never let me down but eventually sold ot when I picked up a DM45 mill.

    I suspect the motor controller in my Steelmaster SM920V was simialar to you and it blew up last year. Never bothered to replace it as I had a 3ph motor and VFD waiting for it, it came with the DRO I bought for it S/H.

  5. #5
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
    Posts
    4,987

    Default

    Hi Fred,

    Post a picture of the board and I will see if I can identify it, though if you have fitted the 3ph motor and VFD, I suspect that it isn't urgent to get it fixed.
    Best Regards:
    Baron J.

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