Testing TV transformer

Discussion in 'General Electronics Chat' started by inwo, Mar 1, 2014.

  1. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
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    Is it worth while buying a ring tester for testing high frequency transformers?

    What I mean is. Will I get a good-bad reading from an unknown transformer?

    Is there another way?

    I have a power supply that overheats the Mosfet and transformer. Outputs about half voltage and shuts down.

    I've eliminated loads one at a time with no change.

    New board is coming, but I never pass up a chance to learn something new.
     
  2. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
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    Like this one.......................
     
  3. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
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    How about ringing with a shunt capacitor and a dc pulse?

    Or watching on a scope while fed with square wave?

    Wouldn't need a tester then.:confused:

    But will it show a shorted turn?
     
  4. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
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    I guess I'll answer myself.:rolleyes::D
    And save some money.

    Feeding a 100khz square wave to a donor transformer makes a beautiful ring pattern on scope.

    Tomorrow I'll look for one with a loose enough winding, to wind a single shorted turn to see how much it damps.

    Then on to the suspect.
     
  5. debe

    Well-Known Member

    Sep 21, 2010
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    This is a very simple shorted turns tester I built about 30yrs ago & still use it for SMPS transformers.
     
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  6. inwo

    Thread Starter Well-Known Member

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    Explain how it works in practice.
    Do you need a reference to tell you whats good or bad?
     
  7. rc3po

    Member

    Feb 12, 2014
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    I have a Blue Ring Tester and it works great. I bought mine as a kit when I started learning electronix last year so I could also practice soldering.
     
  8. debe

    Well-Known Member

    Sep 21, 2010
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    OOps, This is the circuit that's used in the previous tester. It runs at about 25Khz when tested with a freq meter. RV1 is adjusted to give just over full scale deflection on the meter. Tr2 is the meter amp. When testing a SMPS transformer, connect leads to the primary windings. If there is a shorted turn in the T/F the meter will drop back to a very low reading, due to excess loading on the oscillator circuit.
     
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  9. inwo

    Thread Starter Well-Known Member

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    I think this will work best for me.
    Shorting one turn with xacto knife flat-lines.:)
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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  11. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
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    Tested the real transformer today. Found it ringless.:)

    That means my 3 weeks work on this set is for naught.

    Even the new PS supply order was canceled.:(

    Any TV guys on here with junk boxes?

    LG 47LB5D
     
  12. debe

    Well-Known Member

    Sep 21, 2010
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    Finaly found the original article. Have recently wrecked an LG LCD TV that had a picture problem. But I only saved the switching MOSFets & diodes & binned the rest. Pretty rare for the transformers to be faulty.
     
  13. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
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    First for me.

    Rare for 10 other parts to fail too.:eek:

    Tried to get a new board twice. Out of stock.

    Found a schematic and parts list. Not helpful. ZD100 not listed nor transformers.:(
     
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