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First electronics repair question

Discussion in 'Troubleshooting and Repair' started by slaquer, Feb 20, 2016.

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  1. slaquer


    Feb 20, 2016
    I was given a Mr. Christmas Piano that "played too fast" and I want to take this opportunity as a simple introduction into repairing electronics at the component level.

    After taking it apart and noticing it was a very simple design (1 diode, capacitor across a motor and that's it) I noticed when looking at the specs of the motor the first problem was they were using the wrong adapter. The motor has a spec from 6v - 12V and the adapter was putting out 36V and it played like it - easily 3 times too fast - maybe more!

    I found a 5V DC adapter and it is still playing a little fast however. So, I have a few questions. The circuit is very simple:

    Small diode where the adapter plugs in which then directly connects to the motor, The motor has a ceramic capacitor marked 104 on it (.01uf). That's basically it.

    I do not know what the original specs were on the original adapter.

    A few questions:

    1) Could it be I just need to reduce voltage a bit more? It is playing maybe 1/4 faster than it should at 5v. Very close

    2) What is the capacitor function? The positive and negative wires runs to the motor and the capacitor sits between those two wires directly soldered to the wires on the motor poles.

    3) I know the voltage is correct to the motor so I am assuming the diode is good.

    4) The capacitor tests .01uf which is right (tested in circuit), but I don't really know what that means and if the capacitor is good or not. Could it be the capacitor is acting like a resistor somehow and it died from the over voltage and the morot is spinning too fast because of this?

  2. Alec_t


    Jul 7, 2015
    Welcome to EP!
    104 indicates 0.1uF. It's an interference suppression cap. The diode is either for reverse polarity protection/prevention, if the original adapter was DC, or for half-wave rectification if the adapter was AC.
    You could try an extra diode or two in series with the motor to reduce the speed.
  3. cjdelphi


    Oct 26, 2011
    Diodes might work or cause it to be a tiny bit slower or tiny bit faster

    Another option is to vary the motor speed with pwm and a potentiometer to fine tune it...
  4. slaquer


    Feb 20, 2016
    I found the original adapter specs - 6vDC/200ma. I am using a 5vDC/240ma adapter.

    So, since it is still playing a little fast, what could be the issue? It's a diode, a capacitor and a motor.

    What is the function of the capacitor running between the poles of the motor? Can it act as a resistor?
  5. davenn

    davenn Moderator

    Sep 5, 2009
    noise interference suppression

    no, unless faulty ... does it look damaged ?
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