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Servo motor acting strange?

Discussion in 'Troubleshooting and Repair' started by Jimbo bob, Aug 31, 2015.

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  1. Jimbo bob

    Jimbo bob

    Oct 8, 2014
    Hi dear enthusiasts,

    I recently bought a PS-050 servo motor. It has a lot of torque. Due to some accidents, the wiring that go to the potentiometer and from there to the circuit board (the green, black and white wires) were ripped apart. Moreover, the orange, brown and red wires may also have been resoldered again possibly in the wrong position. That said I did have a look at a circuit board of the servo that I found online and the order seemed fine. In the photo I you can see that I have switched the black and white wire as I thought that is what one of the schematics illustrated. I think after the accident, the potentiometer of the servo is not working properly for two reasons:

    1. The total resistance of the pot seems to be changing as I rotate it. As far as I know, the resistance across two terminal should change and the terminal which has the total resistance of the pot should stay constant. In this case the resistance across all different combinations of terminals changes, which is strange to me.

    2. When I power the motor on with 12V, the DC motor keeps rotating in a given direction regardless of the position of the pot. This also was the case when the black and white wires were not switched yet.

    So what do you think? Is my pot gone or there is something with the wiring?

    Here is the link to schematics that I looked at:

    (The schematics are almost towards the end of the page)

    I have also attached some pictures.
    Many thanks in advance!!!:D:D

    Attached Files:

  2. Bluejets


    Oct 5, 2014
    Servos do not take kindly to the supply being reversed.
    I would say that in reversing the brown orange and red that you have blown the main board somewhere.
    One other query, why is there a green wire on a terminal marked "red"..and black and white transposed??
    Jimbo bob likes this.
  3. Jimbo bob

    Jimbo bob

    Oct 8, 2014
    I see. The thing is I am not really sure that the reason it does not work is reversing the brown, orange and red wires. How can I confirm whether that is the issue? They may be in the right position.
    Ha Ha :D. I have no idea about the green wire. It was there to begin with. Probably they ran out of red wires.
  4. Jimbo bob

    Jimbo bob

    Oct 8, 2014
    Also I forgot to mention that I transposed the black and white, because based on one of the circuit diagrams that I found (which I have linked) I thought the wires should be connected other way around (Although it is counter intuitive). But the point is that did not make any difference in servo's crooked performance as I mentioned in my original post. Moreover, I confirmed that the red, brown and orange wires were not resoldered and remained intact from the accident.
  5. Martaine2005


    May 12, 2015
    Hi Jimbo,
    @Bluejets has already pointed out some important points to you.
    The Brown is negative, Red is positive and Orange is signal.
    The other colours are marked on the board . I would re-solder all wires to corresponding board markings and start from fresh.

    If your servo is going in one direction only, check the gears. If the gear teeth or stopper positions have broken off or worn down, the motor wont 'return' in the opposite direction.

    Jimbo bob likes this.
  6. Jimbo bob

    Jimbo bob

    Oct 8, 2014
    Cheers!!:) I am going to try to change the potentiometer and the worn out bits, hopefully it works:D
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