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Discussion in 'Electronic Repair' started by Chris F., Dec 1, 2003.

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  1. Chris F.

    Chris F. Guest

    Me again with this old Sony projection set (KPR-36XBR). I see my last post
    didn't get any replies, perhaps I was a bit too long-winded. I'll keep this
    message short.
    I located a service manual for a KP-46XBRxx, and it suggested that the
    high voltage block does not act as a bleeder resistor, instead, it contains
    a cap and supplies a low-voltage reference signal to the HV shutdown
    circuit. So it may not be the problem after all.
    All I want to know for now is, how can I modify the set to reduce the high
    voltage? As I mentioned before, the B+ is regulating properly, and the
    design suggests that the HV is regulated by increasing/decreasing the
    amplitude of the horiz. osc signal. Is it possible that I could put a
    potentiometer, in series with the base of the HOT or something?
    I basically just need it to the point, where it will run without arcing
    and blowing the HOT. I've blown at least 10 of them already!
    Thanks for any advice you can offer.
     
  2. Jerry G.

    Jerry G. Guest

    I cannot tell you how to modify the set, but it would be best to fix the
    fault. In a standard set, the HV is regulated not by changing the amplitude
    of the drive pulses, but is done by changing the duty cycle slightly. The
    amplitude change will change the scan width, if the scans are derived from
    the HV drive, as done in most TV sets. There is some type of feedback to
    sense the HV current, and this goes back to the scan gen circuit area to be
    processed.

    --

    Greetings,

    Jerry Greenberg GLG Technologies GLG
    =========================================
    WebPage http://www.zoom-one.com
    Electronics http://www.zoom-one.com/electron.htm
    =========================================


    Me again with this old Sony projection set (KPR-36XBR). I see my last post
    didn't get any replies, perhaps I was a bit too long-winded. I'll keep this
    message short.
    I located a service manual for a KP-46XBRxx, and it suggested that the
    high voltage block does not act as a bleeder resistor, instead, it contains
    a cap and supplies a low-voltage reference signal to the HV shutdown
    circuit. So it may not be the problem after all.
    All I want to know for now is, how can I modify the set to reduce the high
    voltage? As I mentioned before, the B+ is regulating properly, and the
    design suggests that the HV is regulated by increasing/decreasing the
    amplitude of the horiz. osc signal. Is it possible that I could put a
    potentiometer, in series with the base of the HOT or something?
    I basically just need it to the point, where it will run without arcing
    and blowing the HOT. I've blown at least 10 of them already!
    Thanks for any advice you can offer.
     
  3. Chris F.

    Chris F. Guest

    I guess I will probably need a service manual. A local supplier can get it
    for me, but $55 Cdn is more than I'd like to invest in this, unless I'm
    reasonably certain it can be fully restored to working condition.
    Pardon my ignorance, but when you say varying the duty cycle, do you mean
    shortening the width of each pulse? There's a chip which is supposed to
    control most of the deflection (NTE 1664), I tried replacing it but it made
    no difference. All caps etc have been checked and none found bad.....
     
  4. David

    David Guest

    FYI flybacks were high failure items on that set after about 10 years.
    The flyback would not only give high HV but would blow the HOT. I
    would do a ring test on the flyback, or run it at reduced B+ voltage
    by putting a 60 watt light bulb in series with the B+ as it goes to
    the flyback and then monitor the HOT collector with o'scope for proper
    waveform.

    David
     
  5. Chris F.

    Chris F. Guest

    Just out of curiosity, what is the normal HV and focus for this set? HV
    measures about 28.5kV and focus is about 12. Seems rather high to me......
    To be honest I've suspected the flyback all along. I will see what I can
    do to modify the set (high-wattage resistor in series with the HOT
    collector, etc) and I might be able to patch it up. Wouldn't be fit to sell,
    but I could still keep it for my own use. I'm not going to shell out the
    money for a new flyback, that's for sure.
    BTW, any ideas on how to clean up the solidified coolant on the CRT
    surfaces??
     
  6. GPG

    GPG Guest

    Check the line output tuning capacitor located across c-e of
    transistor. If this goes o/c the eht will go through the roof.
     
  7. Jason D.

    Jason D. Guest

    Hmm.. and tend to blow the HOT instantly. Found this out hard way
    when I forgot to install that larger of two cap. :)

    Btw, which one of duo caps are you talking about? There is two across
    C-E of HOT. One is typically 10nF, other one is appox 680pF for
    example in a philips set.

    In other set, like zenith, I see multiple smaller caps like 470pF,
    two, three, even four along with a few nF value cap.

    Cheers,

    Wizard
     
  8. Chris F.

    Chris F. Guest

    Already checked that possibility, cap checked good.
    I should also mention that the HOT is running nice and cool, which seems
    really odd considering the HV problem. And, the HOT now only blows when the
    HV discharges to the chassis (Bang!).
    I noticed that, because of the small CRTs, the anode caps are extremely
    close to the metal chassis, and I suspect that even under normal
    circumstances arcing could be a problem. My current plan is to completely
    seal the anode caps with silicone, and insulate that area of the chassis,
    thereby eliminating any alternate path for the HV to take. I have a feeling
    that might just solve the problem.
    But first I must get some more HOTs. Blew another one last night, that makes
    #11 I think..... >:-(
     
  9. GPG

    GPG Guest

    Btw, which one of duo caps are you talking about? There is two across
    They are all important. The multiple values all add up. Some sets in
    the past had specially made non-standard values, eg philips k9, 11.9
    nF
     
  10. GPG

    GPG Guest

    do to modify the set (high-wattage resistor in series with the HOT
    This will cause changes in picture size due to poor eht regulation
    Do not change the base drive. The eht is not regulated in any way.
    http://members.aol.com/JURB6006/HRATE.htm
     
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