Benchtop Pro MD95 Dremel Burnt resistor now works at Full speed only

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  • DJ_MIX
    Senior Member
    • May 2005
    • 118

    #1

    Benchtop Pro MD95 Dremel Burnt resistor now works at Full speed only

    Guys need your help.
    I believe it got wet a bit which then cause it to only run at full speed, no longer can adjust speed.

    Opened up and notice burn near resistor. I guess I need new resistor but what value? I did not test any further, I guess I can remove resistor and check.

    Let me know what you think. Also what is ntc 60?
    Attached Files
  • R_J
    Badcaps Legend
    • Jun 2012
    • 9514
    • Canada

    #2
    Re: Benchtop Pro MD95 Dremel Burnt resistor now works at Full speed only

    I would guess the triac is shorted, looks like that resistors been running hot for a while and it may still be ok. Remove it and check its value, look and see if there are any values still visible on the resistor
    Last edited by R_J; 06-04-2018, 04:02 PM.

    Comment

    • DJ_MIX
      Senior Member
      • May 2005
      • 118

      #3
      Re: Benchtop Pro MD95 Dremel Burnt resistor now works at Full speed only

      Remove it but didn't see any values on the resistor. It did measure 5.2 ohms with multi meter. Which one would be the triac?

      Comment

      • petehall347
        Badcaps Legend
        • Jan 2015
        • 4422
        • United Kingdom

        #4
        Re: Benchtop Pro MD95 Dremel Burnt resistor now works at Full speed only

        yes the triac is suspect . or the pot is damaged .. maybe still damp .

        Comment

        • petehall347
          Badcaps Legend
          • Jan 2015
          • 4422
          • United Kingdom

          #5
          Re: Benchtop Pro MD95 Dremel Burnt resistor now works at Full speed only

          triac is the one with 3 legs

          Comment

          • DJ_MIX
            Senior Member
            • May 2005
            • 118

            #6
            Re: Benchtop Pro MD95 Dremel Burnt resistor now works at Full speed only

            Thanks Guys, the trace near the resistor was lifting so I glued it back. Once I but it back I will retest.

            Comment

            • R_J
              Badcaps Legend
              • Jun 2012
              • 9514
              • Canada

              #7
              Re: Benchtop Pro MD95 Dremel Burnt resistor now works at Full speed only

              Remove the old solder and resolder the resistor, if the trace is bad just replace it with a piece of wire, Provide the number off the triac (3 leg part) if there is one.
              Last edited by R_J; 06-04-2018, 05:51 PM.

              Comment

              • redwire
                Badcaps Legend
                • Dec 2010
                • 3900
                • Canada

                #8
                Re: Benchtop Pro MD95 Dremel Burnt resistor now works at Full speed only

                It looks like the speed controller was overloaded, cooked the resistor and triac. The NTC was useless, it was supposed to limit power.

                Drew a schematic but not sure what the cooked R3 resistor's value is.
                The circuit did not make sense unless there is a diac or something underneath the hot glue blob.

                If you can give the resistor ohms and triac part number, I will update the sch.
                Attached Files

                Comment

                • DJ_MIX
                  Senior Member
                  • May 2005
                  • 118

                  #9
                  Re: Benchtop Pro MD95 Dremel Burnt resistor now works at Full speed only

                  WOW, thanks

                  The resistor is mwntion above at 5.2 ohms
                  triac is Z0409MF A149

                  Sorry had no time to mess with unit.

                  Comment

                  • R_J
                    Badcaps Legend
                    • Jun 2012
                    • 9514
                    • Canada

                    #10
                    Re: Benchtop Pro MD95 Dremel Burnt resistor now works at Full speed only

                    It's very likely the triac shorted, that would cause the motor to run full speed

                    Comment

                    • DJ_MIX
                      Senior Member
                      • May 2005
                      • 118

                      #11
                      Re: Benchtop Pro MD95 Dremel Burnt resistor now works at Full speed only

                      I will remove and try to test it.

                      Comment

                      • DJ_MIX
                        Senior Member
                        • May 2005
                        • 118

                        #12
                        Re: Benchtop Pro MD95 Dremel Burnt resistor now works at Full speed only

                        Problem solved, appears it was the Pot, I cleaned it and now have variable speeds..

                        Comment

                        • sam_sam_sam
                          Badcaps Legend
                          • Jul 2011
                          • 6018
                          • USA

                          #13
                          Re: Benchtop Pro MD95 Dremel Burnt resistor now works at Full speed only

                          If you can find a new pot I would recommend replacing it
                          It might do the same thing again

                          Comment

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