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Sony shut down

Discussion in 'Electronic Repair' started by Golf, May 31, 2007.

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  1. Golf

    Golf Guest

    Sony model #HT32744. Hit power button, relay clicks, high voltage
    starts up, then relay clicks a few times and no go. Checked bridge
    rectifier, shows voltage while starting up, but goes to nothing when
    relays click. Had disconnected power to HV board before, and after I
    did this. No difference. I don't have a schematic, and have no info on
    this particular model #, besides having only about 2-3 years
    experience. I'm aware several things could cause this, but without a
    service manual, I'm shooting in the dark. Looking for a little advice
    on this set as well. Thank you to all replies.
     
  2. Golf

    Golf Guest

    Forgot to mention, I checked all diodes, resistors in the power
    supply. Not sure how to check the voltage regulator though. Thanks.
     
  3. Golf

    Golf Guest

    Also forgot to mention, this isn't a Sony. It's a Sanyo. Too many sets
    on the bench!. Thanks group.
     
  4. Golf

    Golf Guest

    Thanks for reply Jamie. The flyback does tick during start up, but I'm
    not sure if this is normal or not. I haven't tried ringing the
    windings or anything yet.
     
  5. Jamie

    Jamie Guest

    HV supply is bad? (FLyBack)? or maybe the HV-TRAnsistor?
     
  6. Jamie

    Jamie Guest

    also, many units derive low voltage from the flyback when it's
    fired up. I have found in some cases where this voltage gets
    rectified, the filter caps are bad.. and other times, devices
    connected to this source are shorted..
    the main PS unit also may monitor this source to know when to
    shut down the unit if voltage is gone or never gets there after
    a couple of sec's
     
  7. Golf

    Golf Guest

    Thanks again. Iv'e checked every cap in the PS and all good. I'm sure
    the main PS isn't the problem. Iv'e also checked several other
    electrolytics, and nothing yet. Again, without a manual or schematic,
    I can only check each component as I go. This may be beyond my
    capability, but I'll reply after the flyback test - even though I was
    told by a tech this can give false results. Thanks again.
     
  8. Meat Plow

    Meat Plow Guest

    How do you know the HV starts up?

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  9. Golf

    Golf Guest

    I can hear it, and feel the static electricity build on the screen.
    But it doesn't stay up long enough to show any raster - only a sec. or
    two. Thanks for the reply. Any suggested checks much appreciated meat.
    You have helped me before.
     
  10. Meat Plow

    Meat Plow Guest

    Sounds like it could be going into X-Ray protection. It will do that if
    the HV goes to high if the tuning in the HV circuit is incorrect. I don't
    recall how old the set is but I used to work on plenty of them in the
    80's and I doubt they got rid of that circuit. There are a couple caps
    in that circuit that provide tuning along with other devices. Sets that
    acted like this I would ramp up on a variable supply and monitor the
    voltage at the anode to troubleshoot it. That's about the extent of my
    help however right or wrong it turns out to be :)
     
  11. Golf

    Golf Guest

    Thanks Meat. Again, this is a SANYO. I f'd up in the original post
    saying it was a Sony. This set is only 3 years old. I agree that it
    may be a protection circuit shutting it down, and I do have a variable
    supply that I can try, and go from there. Thanks for the info.
     
  12. Meat Plow

    Meat Plow Guest

    You need a HV probe for the anode. Start it out around 60 volts and see if
    it fires. If not jump up 5 volts until you get it to start. Look at the
    HV, if it goes above 25KV it should shut down. Have fun and watch those
    lethal voltages. Let me know what you find. Watch the chassis too because
    most of them are above ground around 200 volts. Don't be brave :)

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  13. Golf

    Golf Guest

    OK, I managed to get the set to stay on around 70V on the variable.
    The high voltage stayed up but the flyback was still ticking. Anode
    checked 18KV and was stable. Set shut down around 80V on variable.
    Checked the raster while HV was up, and saw a faint glow in the middle
    of the set (about 1" square) that pulsed with the flyback ticking. If
    I vary the voltage below or above 70V, the relays in the PS start
    clicking like crazy. I suppose the flyback could be bad even though
    the HV is stable?
     
  14. Meat Plow

    Meat Plow Guest

    Unless there was a common problem with flybacks on this chassis I would
    not include it on my possible list. That's one problem I have being out of
    the loop and not knowing these things. When the set does shut down at 80
    what was the HV? You might want to get your wallet out and snag some
    service literature and check some voltages. Also you could look for some
    cold solder joints in the SMPS and HV block/flyback before you spend money
    because I've read about issues with newer sets and lead-free solder.

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  15. Golf

    Golf Guest

    Thanks. I am now looking in the SMPS. Trying to find info on the
    switching IC to see if I can determine if it may be a problem. I
    already checked all componenets in this area. Haven't checked solder
    joints yet. BTW - the HV was steady 18KV when the set shut down.
     
  16. Meat Plow

    Meat Plow Guest

    Ok cool. I'm sure you'll find it.
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  17. Sony model #HT32744.

    Shucks! I thought this was an announcement that Sony, USA had closed its
    doors...
     
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