Please help me repair power supply

Discussion in 'General Electronics Chat' started by nozit7022, Nov 8, 2015.

  1. nozit7022

    Thread Starter New Member

    Aug 2, 2015
    Hi, good day. I'am electrician by profession. I would like to explore on the electronic side. I'm trying to repair the power supply but i'am stuck. There is no output voltage. I check on the bridge diode and there is output until in the primary side of the transformer and no on the secondary. Attached the pics of power supply. I hope you have time to help me. Thanks and GOD BLESS
  2. bwilliams60

    Well-Known Member

    Nov 18, 2012
    What is the voltage (DC) across the large cap? What is the voltage coming in and the voltage on the primary side of the transformer?
  3. Jony130

    AAC Fanatic!

    Feb 17, 2009
    nozit7022 likes this.
  4. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    What you have there is a switchmode psu, the Top227 is an ic, and if its blown up it wont work, you need to measure the voltage on the chip.
    Hypatia's Protege likes this.
  5. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
    Please be advised that the pictured PSU is an SMPS -- Your DMM/VOM may not be responsive or accurate at the (switching) frequencies/waveforms involved... --- You are best advised to focus upon DC measurements (electrolytic and other high-value capacitors being convenient test points)...

    Best regards and good luck!:)
  6. ian field

    AAC Fanatic!

    Oct 27, 2012
    I'd advise against poking about with DMM prods - those Power Integrations chips can be a bit temperamental. They have a bit of a tendency to blow a crater in the plastic encapsulation when they go bang.

    First I'd test/replace all/any small electrolytics as routine maintenance.

    Very often a shorted secondary side rectifier shuts the PSU down, but I'd examine any power resistor between the chip and the negative of the reservoir electrolytic. Sometimes that blows open before the chip explodes.

    There's usually a high resistance start up resistor that can go high or open.
  7. #12


    Nov 30, 2010
    That yellow transformer looks burnt on its bobbin, but the photo is rather poor quality. I can't be sure.
  8. ian field

    AAC Fanatic!

    Oct 27, 2012
    Those transformers are vacuum impregnated with varnish - then baked.
  9. hp1729

    Well-Known Member

    Nov 23, 2015
    Attached is a data sheet for the TOP227. The schematic on it may be similar to your power supply.
  10. MikeML

    AAC Fanatic!

    Oct 2, 2009
    SMPS's are a really bad circuit to learn on... A bunch of ways to kill yourself or your test equipment. If you insist on poking around in it, get yourself an isolation transformer, like this.