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Testing The Internal High Voltage Diode In Flyback Transformer

By on April 19, 2010

testing flyback

A leaky or shorted internal diode in the flyback transformer of a CRT TV or Monitor would cause the set to shutdown upon power on, power blink and even blowing some of the corresponding components like the HOT, B+ FET and B+ coil. Usually if the diode have a direct short circuit it will be easily detect by checking the connection between the anode and the ABL line using analog meter set to X 10 K ohm range. If the diode is leaky then it would be hard to confirm it with the analog meter.

In order to solve the problem you can use two analog meter set to x 10 k ohm and connect the meters like a battery in series an then test from anode to any of the flyback pin. A good diode will usually have only reading. If there is a pin that shows two reading then the internal diode had shorted. It is as simple as that!

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37 Comments

  1. janaka

    April 19, 2010 at 1:46 pm

    A good diode will usually have only reading. If there is a pin that shows two reading then the internal diode had shorted. It is as simple as that!
    A good diode will usually have only reading
    what is two reading?

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  2. admin

    April 20, 2010 at 8:11 am

    Hi Janaka,

    Two reading means shorted reading when tested both ways with your probes.

    Jestine

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  3. Steve Hearns

    April 23, 2010 at 11:41 pm

    Hi Jestine, not all fbt only have (1) diode. Some have triplers built into secondary, and the diodes are tied in-between sections of windings of the primary, so unless all diodes are shorted, you will still see open reading on multimeter. With these kinds of fbt, only way to test them is by replacing with a known good fbt. Older designs of display equipment usually have tripler as separate block connected to anode of transformer. the block has tripler , capacitor and bleeder resistor installed all inside and flyback transformer case is just the coil windings.

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  4. admin

    April 24, 2010 at 8:21 am

    HI Steve,

    Thanks for sharing!

    Jestine

    Likes(0)Dislikes(0)
  5. kanna

    November 25, 2010 at 2:11 am

    very use full

    Likes(0)Dislikes(0)
  6. Masese

    December 21, 2010 at 9:52 am

    Hi Jestineyong, that was very usefull to me.

    Likes(0)Dislikes(0)
  7. ABRAHAM

    January 14, 2011 at 12:45 pm

    with a leaky flyback there is normal picture and sound in the tv but
    after a few seconds the bleeder resistor providing the screen voltage to G2 will start smoking or become redhot, is this true,
    have I to replace the flyback
    I shall be glad if you can guide me

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  8. admin

    January 14, 2011 at 9:46 pm

    HI Abraham,

    If the bleeder resistor have problem it will affect the g2 and focus voltage thus it will affect the display brightness and the sharpness of the picture. If you found a flyback to be in bad condition, yes you are encourage to replace it.

    Jestine

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  9. lito mendoza

    September 28, 2011 at 7:58 am

    hello jestine,

    can a bad divider/pot on the flyback cause brightness to change intermittently and the screen voltage to drift around?

    thanks,

    lito

    Likes(0)Dislikes(0)
  10. admin

    September 29, 2011 at 8:40 am

    Hi lito,

    Yes it can.

    Jestine

    Likes(0)Dislikes(0)
  11. brhanu

    January 13, 2012 at 1:45 pm

    LG TV the HOT burn to replace the HOT there no display it is only the green light.

    Likes(0)Dislikes(0)
  12. admin

    January 13, 2012 at 8:59 pm

    HI Brhanu,

    Any B+ voltage to the flyback. Did you hear the flyback high voltage sound?

    Jestine

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  13. bhavesh

    July 17, 2012 at 12:24 am

     dear sir.Admin
    wipro 17 ''crt  monitor
    no display but led complet work

    Likes(0)Dislikes(0)
    • Jestine Yong

      July 17, 2012 at 8:09 am

      HI Bhavesh,

      Is there any high voltage? Is there G2 and heater voltage at the CRT board?

      Jestine

      Likes(1)Dislikes(0)
  14. austin

    October 9, 2013 at 7:06 am

    my tv show only vertical line at the center of screen

    Likes(0)Dislikes(0)
    • Jestine Yong

      October 9, 2013 at 10:57 am

      HI Austin,

      Check the horizontal yoke coil area. It can be dry joints or have an open winding in horizontal yoke coil.

      Jestine

      Likes(0)Dislikes(0)
  15. ahmed ibrahim

    November 28, 2013 at 3:50 am

    Dear Jestin yong I would like to offer my greatest thunk for U. your electronics tips that U send me every day has a grate influence in my life.So please don't stop sending.More over I need the name of crt tv internal components with their photo please.THUNK

    Likes(0)Dislikes(0)
    • Jestine Yong

      November 28, 2013 at 8:22 am

      Hi Ahmed,

      Sorry I do not have. Try visit the link below where you can learn from the crt monitor.CRT Monitor and tv have some similarities except that crt tv have additional tuner,IF and sound. I suggest that you visit this link also to get Humphrey's ebook:

      http://www.electronicrepairguide.com/crt-tv-repair-ebook.html

      Jestine

      Likes(0)Dislikes(0)
  16. ahmed ibrahim

    November 28, 2013 at 3:59 am

    I face samsung 15'' crt tv with picture ok no sound.I check the speaker and the line it is ok.i can't go further.can U help me Jestin please

    Likes(1)Dislikes(0)
    • Jestine Yong

      November 28, 2013 at 8:16 am

      Hi Ahmed,

      Try check if there is dc supply to the audio amplifier or not.

      Jestine

      Likes(0)Dislikes(0)
  17. bongsky

    February 9, 2014 at 8:53 pm

    HI Jestine thanks for always sharing with us your knowledge in electronic repair good day.

    Likes(0)Dislikes(0)
  18. ahmed

    May 23, 2014 at 7:03 pm

    hi justin
    how to test integrated circuit

    Likes(0)Dislikes(0)
    • Jestine Yong

      May 23, 2014 at 8:26 pm

      HI Ahmed,

      Check on this link:

      https://www.jestineyong.com/can-we-test-ic-using-a-multimeter/

      Jestine

      Likes(1)Dislikes(0)
      • Robert

        May 23, 2014 at 9:01 pm

        The search box doesn't work. It always puts the X on the search button so when you click on it, it erases what you put in it.

        Likes(0)Dislikes(0)
        • Jestine Yong

          May 23, 2014 at 10:12 pm

          Hi Robert,

          I have tested on the search box and it worked. I typed ESR meter in the search box and pressed enter and the result came out.

          Jestine

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          • Robert

            May 24, 2014 at 12:13 am

            It doesn't work for me, and never has. As soon as I start typing,
            an x appears over the search button. It's always been that way but I never said anything.
            Maybe it works for you because you are the administrator, I'm not sure.

            Likes(0)Dislikes(0)
            • Jestine Yong

              May 24, 2014 at 10:42 am

              HI Robert,

              I have tried logging out and still it can work. Perhaps you try to use another browser to see how it goes.

              Jestine

              Likes(0)Dislikes(0)
  19. Virgilio M. Villarba jr.

    August 13, 2015 at 3:57 pm

    HI""
    Good Day Sir Justine Yong, I work ask electronic Technician, Pls. Help Me Where i cant buy your Book to Read. To Up grade about me Knowledge in electronic. Mosley I Repaired TV LCD,LED,Monitor PC and Normal TV Monitor and Applier. I Really Need the Book to Guide Me Thank you very much for kindly Read my email

    Likes(0)Dislikes(1)
    • Jestine Yong

      August 14, 2015 at 8:39 am

      Hi Virgilio,

      You can visit this link below to buy the ebook:

      https://www.jestineyong.com/resources-2/

      Jestine

      Likes(0)Dislikes(0)
  20. JamesFD

    November 26, 2015 at 3:13 am

    I so mush love sits like this. Thanks alot for this sir God bless you.
    sir my tv(daewoo dyt-28a8gbs. 28 inchs) is making some kiki..like continueos sound and the display shortened if displaying a white/bright background. i have be managing it this way. How can i fix it? i need help

    Likes(0)Dislikes(0)
    • Jestine Yong

      November 27, 2015 at 9:22 am

      Hi James,

      Have you checked if the B+ voltage to the flyback good?

      Jestine

      Likes(0)Dislikes(0)
  21. Yahiya

    December 4, 2015 at 7:47 pm

    Hi sir,
    My Philips flat crt tv hout not oscilating now 130v hout transistor ok but no oscillation fly backtra.. pls help me

    Likes(0)Dislikes(0)
    • Jestine Yong

      December 4, 2015 at 10:35 pm

      HI Yahiya,

      Check if there is waveform going into the base of HOT.

      Jestine

      Likes(0)Dislikes(0)
  22. Patrick Chinkhota

    December 4, 2019 at 12:10 pm

    My TV's, of of different make ended up with similar problems- popping sounds and pictures intermittent disappearances.what is the probable cause on this?
    Help me please!

    Likes(0)Dislikes(0)
    • Jestine Yong

      December 5, 2019 at 8:14 am

      Hi Patrick,

      Probably arcing in the flyback. You need to open the TV and check.

      Jestine

      Likes(0)Dislikes(0)
  23. ak.dev

    July 5, 2020 at 12:15 am

    Hi Justine,

    I was searching "How to test the internal diode of EHT in a CRT TV" and came across your post. This thread had started in 2010 and your last reply was on Dec 2019. I hope you are still available to reply questions. Here is my question with a little history.

    I had a very old 21" color TV that didn't have AV inputs. To connect to SET TOP BOX, I identified the video and audio input points on the motherboard. I had also disconnected the internal SMPS and connected external SMPS. It worked without any problem for over two years.

    The problem started recently. The picture will suddenly go blank for few minutes and then start on its own. I thought it may have the external SMPS promlem and replaced with new SMPS. However as soon I connected the new SMPS and switched on the TV, I heard a low blast sound and the display went blank. The screen didn't pull hairs on my hand when I touched the screen indicating the there is no anode voltage.

    Since then I have checked most of the components and associated voltages and all seems to be OK. Sound part is working. All voltages on the picture tube pins are OK. My last doubt is about anode voltage. As I don't have anode voltage prob, I want to be sure that internal diodes in the EHT are OK.

    Instead of two analog meters, I had used a 21 volt DC source to check the voltage between EHT's 7th pin and the anode. This voltage is about 4.5 volts. Reversing the meter leads gives no reading indicating high internal resistance.

    What conclusion can I draw from these readings?

    Likes(0)Dislikes(0)
    • Jestine Yong

      July 7, 2020 at 9:12 pm

      Hi A.k,

      A flyback need B+ voltage and a pulse to base of HOT. The secondary winding output of flyback also should not have any shorted components. A shorted pc tube also can cause the flyback to malfunction. Flyback is a high voltage device and by checking the internal diode only is not adequate. This means it can checked to be good but fail when under load. If there is presence of B+ voltage and pulse to base of HOT then chances is high the flyback could be the problem. Make sure also the flyback primary winding is not shorted and open circuit.

      Jestine

      Likes(0)Dislikes(0)

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