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Testing darfon transformers

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    Testing darfon transformers

    Hi - I have been a member for some months and up until now have just used the site asa super source of information. I know almost nothing about electronics but have always enjoyed the challenge of trying to mend things. I initially started by buying a few faulty dell laptops mixing and matching parts to build a working one which progressed to 4 or 5. One model which shorts out can sometimes be “fixed” by removing a capacitor. I then moved on LCD Monitors – lots began to appear on ebay as “wont turn on” . By reading what others were doing on here I guessed this was due to bad capacitors and managed to get a few working. One item advertised as a monitor was a 32 inch tv which cost about 1$ and only needed a small capacitor replacing and it has now worked fine for 10 months. I recently re capped a 20 inch tv which was a partial success in that it works great but until I mended it I hadn’t realised the inner screen was broken – some you win….!! Ill keep checking ebay to see if I can get a panel.

    I am lucky in that I live walking distance from CPC which is a branch of Farnall in the UK so I don’t have to pay Postage on small items.

    My current problem is a 27 inch tv which I bought (again for a couple of dollars ) and
    it had a faulty power supply – no parts required just a dry/burnt solder joint. It has been
    ok for a while but now has 2sec to black. I have read a few items on here and I am pretty sure I need a new Darfon inverter transformer. I am about to order one having carried out
    A simple resistance check across pins 1 -8 and 4-5 –all show similar (950) except one (T2)Which gives no reading at all on pins 4-5.. At that point I was quite happy with my
    diagnosis ( despite the poor voltmeter I am using – one not recommended on this site)
    but I then thought I’ll check across some other pins 1-4 and 5-8.
    1 -4 5-8

    T1 nr nr = No reading
    T2 0 nr
    T3 nr nr
    T4 0 1908
    T5 nr nr
    T6 0 1908
    T7 nr nr

    I am guessing that if T2 had a reading on pins 1-8 then it would have
    a reading on pins 5-8.
    My question is would it be correct for T 2 ,4 and 6 to have the 1908 readings
    and T1 ,3,5 and 7 to have no reading. I am asking because (a) I should have thought they would all be the same and (b)if I need to buy more than 3 transformers I may as well buy a working board . Im sure that this is a simple query for some of you having read so many of the other difficult ones you have answered.
    Attached Files
    Last edited by selldoor; 10-31-2011, 10:30 AM. Reason: Useful info link for all
    Please upload pictures using attachment function when ask for help on the repair
    http://www.badcaps.net/forum/showthread.php?t=39740

    #2
    Re: Testing darfon transformers

    I believe someone once asked what resistances should be for darfons. Whilsy mine is not on this list it may help others - the site also has other info and pictures
    http://www.lcdparts.net/Transformer3D.aspx
    Please upload pictures using attachment function when ask for help on the repair
    http://www.badcaps.net/forum/showthread.php?t=39740

    Comment


      #3
      Re: Testing darfon transformers

      If you are measuring in circuit, concentrate on the 1-8 and 4-5 measurements. There are additional components connected to the other pins that will distort your readings. The failure mode on these transformers are an open secondary. The secondaries are wound with very thin wire which is prone to breakage; the primaries are wound with a heavier wire.

      PlainBill
      For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

      Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

      Comment


        #4
        Re: Testing darfon transformers

        Hi - Thanks PlainBill - I hoped someone would say that. I was measuring in circuit. Have now managed to remove the suspect transformer. Took some effort mind, naturally couldnt find my de solder braid but improvised with thin tv aerial coax (braided part)loaded with flux. Got most of the solder off then revisited each contact passing 3 amp fuse wire between the pins and pads whilst meltiing the remaining solder and a little upward pressure with a small lever. Good job its only one to remove!!.
        Tested the pads/traces back to next visible point and they seem ok.
        Transformer doesnt look burnt or damaged but still no reading on pins 4-5 so I have ordered a new one. Will update when I get it all back together.
        Please upload pictures using attachment function when ask for help on the repair
        http://www.badcaps.net/forum/showthread.php?t=39740

        Comment


          #5
          Re: Testing darfon transformers

          Transformer came today (Wow- cant believe the quick service) I have put it in and
          TV works great. - hopefully for a few months at least.
          Thanks for the input PlainBill.
          Please upload pictures using attachment function when ask for help on the repair
          http://www.badcaps.net/forum/showthread.php?t=39740

          Comment

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