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TV/Monitor: Protecting HOT from secondary breakdown

Discussion in 'Electronic Design' started by L.Chung, Jan 16, 2005.

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  1. L.Chung

    L.Chung Guest


    After replacing the HOT and doing power up check, its usual to put in
    series a lamp bulb to limit the current. The problem comes after the
    lamp bulb is removed and full working voltage is fed to the circuit.

    There is the possibility of HOT damaged instantly via HV secondary
    breakdown if there is some remaining fault in the rest of the circuit.
    As I understand from surfing the net, the HOT is usually operates at
    some 80% of its highest breakdown voltage Vceo.

    I was wondering is it possible to put in parallel a string of
    varistors (or a series of neon bulbs with voltage grading resistors)
    from HOT collector to 0V so as to act as HV protection during the
    final test. After the max. coillector flyback pulse amplitute have
    been measured and confirmed using a 100:1 probe, the varistors can be

    In addition, if I can build a device which impose a fixed(settable)
    voltage drop with current limit, would it be possible to use it in
    series with the horizontal B+ to bring up the voltage to the Horiz.
    stage gradually?

    Thanks in advance for your reply.


  2. Rich Grise

    Rich Grise Guest

    I have no idea where you got this idea. When you replace the defective
    part, the circuit is supposed to operate normally.

    What you need to do is diagnose the actual problem that is causing your
    HOT to let the magic smoke out, then when the rest of the circuit is
    repaired (and the HOT replaced for the last time), your new HOT will work
    just fine.

    Good Luck!
  3. j.b. miller

    j.b. miller Guest

    I've given up trying to fix monitors. ANything out of warranty isn't worth a
    penny and the really new ones only have SMT on board. The garbage guys just
    left with 10 SVGA types, all 15 or 17".
    Sign of the times.
    As to TVs, heck I don't even bother taking a look. the rest of the consumer
    stuff is the same. hace 2 'offshore,what isn't ?) DVD players, less than 1
    year old(90 day war), both need new transports. Let's see $30 for the parts,
    $50 for labour,$20 taxes and some gas = $100. For $50 you can get another
    New DVD player with 'more features', OK, more landfill.....Ok I've
    Some things just aren't worth fixin'..
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