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Can out of spec capacitors cause intermittent motor start problems?

Discussion in 'Turntables' started by JamVal, Feb 13, 2018.

  1. JamVal

    JamVal Super Member

    Messages:
    2,734
    Location:
    Buffalo, NY
    Technics SL-QD33 with intermittent platter motor start problem.

    Usually it works as it should, but once in awhile not. Seems to be a common problem with this deck.

    I read this thread which concluded the problem is with capacitors.
    audiokarma.org/forums/index.php?threads/technics-sl-qd33-turntable-some-repair-tips.781772/

    I've tried to identify when a malfunction occurs - and it seems to happen after a longer period of not being used, or when the tonearm is moved manually. I get it back in sequence by powering it off and rotating the platter about half a turn.

    I am not a tech, but I am dubious about bad capacitors causing an intermittent platter motor start issue. Most of the time the motor starts as it should; once in awhile it does not. So Would bad capacitors cause an intermittent motor start problem? Seems to me if they were bad I wouldn't be able to get it going again.
     

     

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  2. alteclipsch

    alteclipsch Super Member

    Messages:
    1,654
    In many capacitor-start motors a failing cap will cause them not to start. In some cases, it depends on where in the cycle it stopped (so the problem is intermittent). I really can't say if this translates to turntables, but capacitors could have something to do with it.
     
  3. kickitagain

    kickitagain Member

    Messages:
    97
    Location:
    Western NY
    I'm not an expert, but I've had similar problems with ac motors.Sometimes they go backwards. Just change the start cap and it should be fine.
     
  4. JamVal

    JamVal Super Member

    Messages:
    2,734
    Location:
    Buffalo, NY
    Thanks for the replies.
    I took the bottom cover off and supported it between 2 tables so I could watch the mechanism work from underneath.
    I don't see anything that looks gunked up with old lube, no binding or hesitation with the arm gears, arms, levers, etc.
    Initially I thought it was more a mechanical issue than electrical, but not after I watched it.
    Thanks again.
     
  5. sregor

    sregor AK Subscriber Subscriber

    Messages:
    3,586
    Location:
    Mass
    Not a cap start AC motor. Problems with caps and direct drive motors are usually weak caps in power supplies. I would be suspicious of microswitches if they use them (haven't looked at manual....)
     
  6. JamVal

    JamVal Super Member

    Messages:
    2,734
    Location:
    Buffalo, NY
    The thread I previously read said that the problem was solved by changing 2200uF 25v cap in the power supply and all the 47uF caps.
    There is a 47uF 16v on the power supply, (2) 47uF 10v and (2) 47uF 6.3v on the motor board, and (2) 47uF 6.3v on he Control Board.

    Total of (7) 47uF caps
    Do I need to match each to the voltage (16v, 10v, 6.3v) or can I just go with all seven at 16v?
     

     

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  7. sregor

    sregor AK Subscriber Subscriber

    Messages:
    3,586
    Location:
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    Higher voltage caps is not a problem. Sometimes size and lead spacing can be important.
     
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  8. WaynerN

    WaynerN AK Subscriber Subscriber

    Messages:
    5,546
    Location:
    Minnesota
    This is a direct drive table. Your problem could be from lots of things.
     
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  9. JamVal

    JamVal Super Member

    Messages:
    2,734
    Location:
    Buffalo, NY
    In this case I fear size may be an issue. The plinth isn't very deep. I have to pull the boards to take some measurements. Service manual parts list gives values but not sizes.
    In the meantime the turntable has been working fine for the past few days.
    Thanks for the reply.
     
  10. WaynerN

    WaynerN AK Subscriber Subscriber

    Messages:
    5,546
    Location:
    Minnesota
    If the motor was a synchronous motor, the motor has 2 sets of windings and the capacitor is used to force motor rotation direction. If this cap fails, the motor could actually turn in the wrong direction. These kinds of motors are used in belt drive turntables.....
     
  11. JamVal

    JamVal Super Member

    Messages:
    2,734
    Location:
    Buffalo, NY
    Thanks. It's been fine the last few days. When it does malfunction, I power it off, rotate the platter 1/2 turn, power back on, and it works. Almost like it needed to be reset mechanically, looking at the service manual the only thing I can see that would be affected by a turn of he platter is the index plate.
    There's been a number of threads about the same or similar problem with this deck but only the one I mention in my original post attempts to offer a solution; capacitors.
    It's sort of low end so I suspect not many owners are willing to spend much time on it.
     

     

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  12. JamVal

    JamVal Super Member

    Messages:
    2,734
    Location:
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    Not sure what the motor is; SM only states DC-Brushless. When it malfunctions the motor does not drive the platter at in either direction.
     

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