Sony TV power supply problem

Discussion in 'Technical Repair' started by DjKrish, Dec 18, 2010.

  1. DjKrish

    Thread Starter New Member

    Dec 18, 2010
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    SONY CRT TV KV-EX34M69

    Hello folks, greetings. I have a issue with my Sony TV 34 inches. When press the power button, the red light lits and blinks with the power relay on the power section switching on and off for more than half an hour. This will go on for about more than half an hour then the TV will be normal and picture with sound will be perfectly fine. Looks like it needs to heat up before it works fine again. Anyone can please help me with this issue? What could be the problem? Bad caps? As far as i concern, if any transistors or resistors faulty, the TV will not work at all until u replace them. So i suspect it could be a problem with caps. To all TV gurus, please advice.

    [​IMG]
     
    Last edited: Dec 18, 2010
  2. mik3

    Senior Member

    Feb 4, 2008
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    Maybe the latching circuit of the relay is defective.
     
  3. DjKrish

    Thread Starter New Member

    Dec 18, 2010
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    U mean the relay itself could be faulty?
     
  4. mik3

    Senior Member

    Feb 4, 2008
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    Yes or the circuit responsible for latching the relay.
     
  5. DjKrish

    Thread Starter New Member

    Dec 18, 2010
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    This relay is on the main board. Its one piece of mainboard which controls everything. No separate boards. Checked components near the relay and related to the circuit, nothing seems to be faulty. All the components seems to be fine.
     
  6. mik3

    Senior Member

    Feb 4, 2008
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    Try to bypass the relay contacts with a switch to see what happens. Do this if you are familiar with the mains voltage. If not hire a technician.
     
  7. DjKrish

    Thread Starter New Member

    Dec 18, 2010
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    u mean short the relay legs with a cable so that its on permanently to see if it works?
     
  8. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    I remember this issue coming up quite often.

    What is the exact model number of the TV?

    It may be a capacitor issue, what is the manufacture date?
     
  9. DjKrish

    Thread Starter New Member

    Dec 18, 2010
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    This TV is about 7 years old. An awesome TV which seldom gives problem. Never spoiled before either. This is the first time. Model KV-EX34M69

    [​IMG]
     
    Last edited: Dec 18, 2010
  10. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    That's not the model that has the common issue.

    Design life of TVs is around 5 years or less lately, mostly to get people to buy newer/bigger systems.

    Some google work did mention that the HV going too high would cause the system to shut down to prevent radiation (X-ray).

    The flyback/HV is a very dangerous system to check, e.g. Potentially Lethal, so I'd suggest a local electronic shop to look at it.
     
    Last edited: Dec 18, 2010
  11. DjKrish

    Thread Starter New Member

    Dec 18, 2010
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    But the problem is the tv works perfectly fine after more than hour an hour of leaving it on. So i doubt its the flyback. The picture is working fine. Theres something thats weak or leaking preventing the unit to start up. If in anyway the flyback is faulty, it wouldn't fire up the picture either. So this is something else. The thing is it fires up and works perfectly after half or 1 hour. Thats the weird thing. So this is definitely some component issue.
     
  12. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    The problem was mentioned as a protection circuit from the flyback voltage going too high, this would result in a picture, but it could also accelerate some electrons beyond what was required to light the phosphors.

    I am not sure if that is your issue or not, it does seem to be heat related though, due to it working once things have worked for a while to 'warm up'. The clicking is the protection relay due to some fault that is correcting itself once things are warmer.

    The "old way" to find the problem would be a can of Freon, and when the set was working, spray different transistors until it turned off or displayed wrong again, and the last one you sprayed was defective. They've stopped selling Freon though. :(

    Look at the electrolytics to see if any show signs of bulging or leaks onto the PC Board. It may be a bad semiconductor as well.

    If you leave the set turned on, does it turn off/fail after a given amount of time (overnight or more)?
     
  13. DjKrish

    Thread Starter New Member

    Dec 18, 2010
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    Nope, it doesn't turn off at all once its turned on. None of the capacitors is bulging or leaking either from the outer look.
     
  14. DjKrish

    Thread Starter New Member

    Dec 18, 2010
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    [​IMG]


    [​IMG]

    This is the schematic diagram of the relay area.
     
    Last edited: Dec 19, 2010
  15. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Quite a lot of comparators and feedback that can trip the relay.

    Doesn't narrow it down a whole lot.

    Since Freon isn't around anymore, I'd suggest a can of Freeze It and hit the transistors one by one while the set is functioning, until it goes into protection when you hit a/one of the bad component(s). It's almost as cold as Freon and will 'shock' the component to work or not, for a while anyway. Usually transistors, transistor looking items on heatsinks first, then electroytic caps, then ICs, then the flyback itself (takes a lot).

    You can also use "Canned Air" dusters, held upside down so liquid comes out, that you can usually find cheaper locally, but doesn't get as cold as quick, but should do the trick to find the faulty component. It is a little clumsy, but cheaper and mostly the same effect if you use a bit more, essentially enough to get the component white with frost.

    A little patience and a couple cans of air, you should find the problem component. Use the plastic straw so you only hit one component at a time. be very careful to not bump into HV lines (mainly flyback and cable to CRT), don't rest arm on CRT, you can get a capacitive charge/shock.

    Sorry I don't have more advice for you, this is troubleshooting, unless you happen to have a schematic with the voltages on it so you can verify with a meter, even then, freezing is usually faster.


    --ETA: People that I've looked at broken electronics for always tell me a variation of "There can't be much wrong with it, it worked just fine until it quit". :D
     
    Last edited: Dec 19, 2010
  16. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Hate to mention this late, but there were a lot of Sony's that size that had cold connections in the vertical output section which would cause the exact symptoms, the power supply would just shut down especially when cold.

    Point is to look over the entire circuit board very closely, it's hard enough to spot cold solder joints but especially the ones that look OK from a glance but upon closer inspection there's a tiny telltale ring that mirrors the hole the component is mounted through.
     
  17. DjKrish

    Thread Starter New Member

    Dec 18, 2010
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    I think i have re-soldered most of the parts ;)
     
  18. marshallf3

    Well-Known Member

    Jul 26, 2010
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    In the vertical, complex pincushion and CRT board circuitry that Sony's have? They've got extensive fault feedbacks to the power supply when something's not right thus are extremely hard to diagnose, same with Pioneer's and Mitsubishi's.
     
  19. loosewire

    AAC Fanatic!

    Apr 25, 2008
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    @ dj drish,why don't you post that nice pink curcuit board and diagram that you posted on the other site you belong too.Maybe the guys could help you with more information. @ the guys,why not repost what voltages and values that you knowwith out getting him in trouble. The heat sinks could cut down glare if he used black grease marker so the camera can take better shot. He has it apart why not get together and put voltages where they go.The last time we had 165 post on a T.V. and two members that did not do the repair before the post ended. Every one set on the side lines,while 100's of members waited for a repair. The T.V. repair has taken a back seat to all the computerprogramers,and gamers.With the economy going south maybe its time for a T.V. revolvuion,taking them apart dealing with the high voltage as in the past,using our book writing members books to trouble shoot. Can't
    think of his name,he's going into reprint. The least you could have done was to tell him don't touch any thing and not do more damage,take a can of freeze to the supected parts. How many times have they popped on,and bad part replaced. Is there a common sense answer to this...........I don,t know anything but, Not to touch my ohm meter to voltage. Knowing what not to do is 90% of the repairs,the 10% you learn before you touch anything. Do we need a seminars section
    for presentations,Is there 20 year limit on factory diagrams.We need more over the counter. All the sound you hear
    would not be there without the microphone............Forest Mims 111 member has trouble shooting books, maybe he
    will read this and do a modern T.V. review. I should be the first to know about all the copyright laws,so I back off
    on some comments.
     
    Last edited: Dec 27, 2010
  20. debe

    Well-Known Member

    Sep 21, 2010
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    The first sugestion by mik3 i wouldhave thaught was the first thing to try? Did you try it? there was no reply. As the relays are clicking & there is only one feed back to the relay circuit to turn them on or off & is not a protection circuit as far as i can see with the limited circ avb. Atleast if they were bridged it would rule out the on/off circuit. The protection circuits only feed back to the SMPS. (Iam asuming you are competant at working in side a TV)
     
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