Connect with us

Power supply help

Discussion in 'Troubleshooting and Repair' started by Mr.fix it_101, Jun 27, 2017.

Scroll to continue with content
  1. Mr.fix it_101

    Mr.fix it_101

    30
    5
    Apr 11, 2015
    Hello to all.
    I am currently working on a power supply that has malfunction. whenever it is turned on by pressing the power button, it starts and run for around 4 minutes then shuts off by itself, then about 2 minutes after, it turns on and repeats the cycle. I thought it was maybe a bad cap or mosfet, but tests proved that they are GOOD!
    The unit has a relay and you can hear it clicking. What could it be that is causing this?
    please help:(
     
  2. davenn

    davenn Moderator

    13,765
    1,920
    Sep 5, 2009
    it would be really good to tell us what make and model the PSU is
     
  3. ramussons

    ramussons

    374
    71
    Jun 10, 2014
    Over Temperature is a possibility. Is there a working cooling fan? Dust on the Heat Sinks?
     
  4. Mr.fix it_101

    Mr.fix it_101

    30
    5
    Apr 11, 2015
    PC8051 - 240G (written on the circuit board)
     
  5. Mr.fix it_101

    Mr.fix it_101

    30
    5
    Apr 11, 2015
    yep. there is a fan that extract heat
     
  6. Alec_t

    Alec_t

    2,927
    797
    Jul 7, 2015
    Sounds like a thermal problem.
    Perhaps the power transistors are no longer making good thermal contact with their heatsinks?
    Dry joint at a power transistor leg?
     
  7. Mr.fix it_101

    Mr.fix it_101

    30
    5
    Apr 11, 2015
    There is a temperature sensor attached to the heatsink. could this be a possible cause?
     
  8. ramussons

    ramussons

    374
    71
    Jun 10, 2014
    When the supply shuts down, can you feel the heat sink for any high temperature? (be careful).
    The temperature sensor could also be the culprit.
     
  9. Mr.fix it_101

    Mr.fix it_101

    30
    5
    Apr 11, 2015
    when the supply shuts down, the heat sink is not HOT. remember that it only runs for 3 minutes then powers off
     
  10. davenn

    davenn Moderator

    13,765
    1,920
    Sep 5, 2009
    OK everyone is just wasting their time doing wild guessing

    how about more info from you
    1) have you obtained any manual or at minimum a schematic ? ---- if so post it or a link to it
    2) how about some photos, internal and external .... make sure the circuit board(s) photos are SHARP, and well lit. that part numbers can be read
     
  11. ramussons

    ramussons

    374
    71
    Jun 10, 2014
    By pass the Temperature Sensor and see what happens.
     
    Mr.fix it_101 likes this.
  12. Mr.fix it_101

    Mr.fix it_101

    30
    5
    Apr 11, 2015
    there is no available circuit diagram for "PC8051 - 240G" board online
     
  13. davenn

    davenn Moderator

    13,765
    1,920
    Sep 5, 2009
    you still haven't clarified WHAT IS THE make and model of the PSU

    is it a stand alone PSU like a lab/workshop PSU ?
    or is it a module out of a TV, computer or some other it of gear ?

    so what about the photos I asked for

    seriously, if you want help, you have to make an effort to help us
     
  14. Mr.fix it_101

    Mr.fix it_101

    30
    5
    Apr 11, 2015
    ramussons last suggestion worked!! when I removed the temp sensor from the circuit, it runs without shutting off. so i replaced it with another good one. :)
    Darn temperature sensor!!
    thx for the help all
     
    davenn likes this.
  15. ramussons

    ramussons

    374
    71
    Jun 10, 2014
    :)
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-