help troubleshooting power supply

Discussion in 'General Electronics Chat' started by Dominic58, Jun 3, 2012.

  1. Dominic58

    Thread Starter New Member

    Jun 3, 2012
    hello this is my first time posting, the power supply in my canon mx700 printer has stopped working partially, i have some trouble shooting experience, but mostly dates back to the 70's so please be patient with me.

    the power supply has a part number on it of k30290, and on the pc board the numbers are PS-A214.

    the primary input is 100 to 240 volts
    and the secondary out put is 32 volts and 24 volts DC.

    im getting the 32 volts ok but when i check the 24 volts i see it on the meter but then it slowly drops to 9.9 volts. if i wait a min or so it will read the 24 volts then it will slowly drop again to 9.9.

    there are some components on the bottom of the pc that my old eyes have a really hard time seeing because there so small, i believe one of them is a transistor and the other two are resistors.

    so far i have checked the two 150 uf caps with my meter and they seem to be fine, the three fuses checked out ok, the diodes checked out ok as well.

    i can post a picture of the power supply as well if it helps.

  2. bertus


    Apr 5, 2008

    The power supply is most likely a switched mode power supply.
    Those can be hard to troubleshoot.

    It looks like there is a overload protection that lets the voltage drop to those 9 volts.
    If the current is low enough the circuit tries again, but the protection get active again, and so on.

    More info on switched mode power supplies can be found here:

    You can post some pictures of both the upper and lower side of the PCB.