Connect with us

Help on how to test this device

Discussion in 'Troubleshooting and Repair' started by mikey5791, Jul 19, 2015.

Thread Status:
Not open for further replies.
Scroll to continue with content
  1. mikey5791

    mikey5791

    173
    16
    Jun 7, 2013
    Hi all,

    Recently I acquired this mini DC supply adapter,but it lack of any cover with missing mains AC cord 220V. The only identification on the pcb is YY 121 but I am not sure what is the output DC voltage.

    Before I connect a new mains AC cord (the two yellow wire),what are the test I need to do on the component level? I have a digital multi meter,an analogue multi meter,digital capacitor tester and a soldering iron. I have basic soldering skills and had successfully repaired a few faulty LCD monitor. For this unknown device, I have checked the continuity of the black square fuse to be ok and all black colour diode is normal (high resistance one side and no resistance the other side).
    Attached five thumbnail pictures for reference.

    Any help and kind advice is appreciated.
     

    Attached Files:

  2. Martaine2005

    Martaine2005

    3,692
    1,006
    May 12, 2015
    Hi Mike,
    It looks like the transformer has snapped! Or is it just the tape around it?
    Secondly, desolder the black DC wires, they look like they are shorting each other.
    Thirdly, the two caps by the DC output should give a clue to the output voltage.
    They will be higher voltage rated than the output.
    The tracers have been beefed up, so it is probably quite a high current output too.

    Wait and see what others say regarding the transformer before trying to power it up..

    Martin
     
  3. Minder

    Minder

    3,182
    691
    Apr 24, 2015
    That just appears to be a outer cover strip, the lamination's look intact to me.
    M.
     
  4. Alec_t

    Alec_t

    3,060
    834
    Jul 7, 2015
    The transformer core looks to have split. One leg isn't vertical. There's a distinct shadow by the gap in the tape in IMG-0927.
     
    davenn likes this.
  5. davenn

    davenn Moderator

    13,947
    1,989
    Sep 5, 2009
    yup agree totally ... the core has snapped

    you are not likely to get a replacement .... the PSU is file 13 ( rubbish bin) bound

    there are no laminations ... its a ferrite core !!

    Dave
     
  6. dorke

    dorke

    2,342
    665
    Jun 20, 2015
    Alec_t is correct-see enlarged photo
    I wouldn't bother with that "junk".
    BTW,It looks such bad quality anyways-get a new one.
     

    Attached Files:

  7. Colin Mitchell

    Colin Mitchell

    1,416
    314
    Aug 31, 2014
    The core has to be touching - otherwise the transformer will heat up too much.
     
  8. mikey5791

    mikey5791

    173
    16
    Jun 7, 2013
    Hi Martaine,Davenn,Alec_t and others

    Thanks for reply.
    Yes the transformer core(black soft magnetic core) has snapped and split on top. Is there any safe way to repair the split core ? Can I use super glue to join? Or is it safer to throw away?

    Martaine,

    FYI, the big green cap near AC is rated 400V 10uF while the middle black cap is 50V 33uF. The two green caps near DC supply is rated 16V 330uF.
    So am I correct to guess the output DC is about 12V ?
    You mentioned that the tracers have been beefed up too with a high current output, but how do you know from your past experience? I am eager to learn.
    I will desolder the black DC wires and check all questionable component before any attempt to power it up.

    Appreciate all suggestions and advice.
     
  9. dorke

    dorke

    2,342
    665
    Jun 20, 2015
    What you have is a direct mains SMPS.
    They have dangerous AC/ DC high voltages in them.that can kill you !
    What is written on IC1,U1,OP1 ?

    Yours is a junk,a very bad quality item(even new)!
    Buy a new one of better quality,they are cheap.

    You can start learning about them here:
    http://www.zl2pd.com/introSMPS.html
     
  10. davenn

    davenn Moderator

    13,947
    1,989
    Sep 5, 2009
    no

    yes :)

    Dave
     
  11. HellasTechn

    HellasTechn

    1,557
    215
    Apr 14, 2013
    The fact that the ferrite has snaped does not necessarily mean that the transformer does not work.

    It may be safer to throw away but still it can be used under certain circumctances given that the transformer is ok and the circuit is not burned.

    The switching mood power supplies are always enclosed in plastic boxes so that the 110 or 220 Vac will not harm anyone.

    In your case it all depends on what you want to do with this psu.
     
  12. HellasTechn

    HellasTechn

    1,557
    215
    Apr 14, 2013
    You should also check the fuse. if it is blown then most likely the mosfet is burned. You should check the mosfet also and the diodes that form the bridge rectifier and the 400Volt smoothing capacitor with your meter.
     
  13. davenn

    davenn Moderator

    13,947
    1,989
    Sep 5, 2009
    but the transformer IS NOT Ok. its physically damaged and as a result trying to use it is really not a good idea
    because the magnetic field through the ferrite core will now be discontinuous, the transformer ratings will be severely derated

    Dave
     
  14. HellasTechn

    HellasTechn

    1,557
    215
    Apr 14, 2013
    Agreed but given that the other components are ok then testing it under mains voltage will probably not do any harm.

    Considering replacement of the board is indeed recommended.
     
  15. mikey5791

    mikey5791

    173
    16
    Jun 7, 2013
    Hi Dorke,

    The info as you requested are as follows:
    U1 (3 leg transistor) 431L
    F20
    JRC
    IC1 (3 leg transistor) H949
    TO......(unclear)
    10.......(unclear)
    OP1 (4 leg opto) 40027
    17A
    F1 (fuse) NSF T2.5A 250V

    Hi HellasTechn,

    Tested the F1 fuse by checking continuity diode test X1, the analogue meter moves showing continuity.
    Is the IC1 the mosfet as you mentioned ? How do I test the mosfet?
    If the mini SMPS is repairable, I wish to use it to power some small project such as electronic kit where current requirement is not that high.

    Appreciate your kind feedback. Thank you all.
     
  16. dorke

    dorke

    2,342
    665
    Jun 20, 2015
    I don't think it is worth repair!
    U1 is a voltage reference/regulator (TL431 like)
    OP1 is an opto-transistor
    IC1 is a power transistor, I think it is probably Bipolar and not Mos.
    The circuit looks similar to the flowing design
     

    Attached Files:

  17. HellasTechn

    HellasTechn

    1,557
    215
    Apr 14, 2013
    I am not sure. i think it is a mos because mosfets are commonly used when it comes to switcing.

    Mikey could you tell us what is written on ic1 ?
     
  18. HellasTechn

    HellasTechn

    1,557
    215
    Apr 14, 2013
    If it really is a mosfet here is a quick way to test it !

     
  19. dorke

    dorke

    2,342
    665
    Jun 20, 2015
    Hi HellasTechn,
    This design seems to lack any "PWM control".
    That is why I think it is a bipolar transistor and not a MOSFET...
     
  20. duke37

    duke37

    5,364
    772
    Jan 9, 2011
    The magnetic circuit may need a gap. This likely since the cores have moved. Do you know what the gap should be and how to set it?

    I strongly suggest that you do not use this device since it depends on isolation from mains to output. If this has been compromised either by a faulty component or a deposit of evaporated metal, you may not be available to post again.
     
    Martaine2005 likes this.
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.
Thread Status:
Not open for further replies.
Electronics Point Logo
Continue to site
Quote of the day

-