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Why does my HOT blow every 2-3 months??

Discussion in 'Electronic Repair' started by tem00, Jul 2, 2007.

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  1. tem00

    tem00 Guest

    I have a Toshiba 65H80 that I replaced the normal HOT section stuff
    including the flyback, some caps, cap block (splitter) and of course
    the HOT, etc. etc.

    It works good about 3 months and blows again. I replace the HOT,
    works for another 3 months.

    B+ seems right.

    Is there anything else that is a common failure point for HOTs that
    I'm overlooking?

    Thanks

    tem00
     
  2. Jamie

    Jamie Guest

    Hmm, maybe you're using incorrect rated HOTranny ?

    are you putting on heat sink compound?.

    are you getting the exact replacement ?

    is it possible it was replaced before by some one else
    that may have used a different number ? something they had
    lying around..

    also, You may want to test for the load current in the B+
    line, it could be exceeding and the regulator could be driving
    the HOT harder to keep it stable. I've seen C+ taps from the HOT
    have leaky caps for lower voltage supplied derived from the HOTxformer.
    etc.. This would cause the flyback to work harder.
    Also, improper adjustments to the screen controls could cause the
    flyback to run hotter along etc...
    theirs a lot of variables here.

    You may also want to test the input to the HOTransistor with a
    scope to see if you're getting full on/off input drive and don't
    have some constant DC there driving the base.
     
  3. b

    b Guest

    tem00 ha escrito:
    check the capacitors in the line drive circuit. these are often rated
    quite low, something like 10-47uF. In one vestel set recently which
    ran hot i changed the cap from 10uF to 22uf and it now runs cooler.

    also check the cap across the c-e of the HOT.

    faulty line o/p transformers can cause these problems too.
    good luck.
    -B
     
  4. Resolder the horizontal drive transformer and associated parts (driver
    transistor, resistors...) ?

    Mark Z.
     
  5. Eeyore

    Eeyore Guest

    Just the HOT ? Do you have to replace all the other above-mentioned too ?

    Graham
     
  6. Simoc

    Simoc Guest

    I'd recommend to check all the electrolytics in the set with an ESR
    meter. I do so always when I have to repair a many years old device
    and the cap test has not been done within years. There are often found
    some "stray bad caps", and they sometimes cause mystic semiconductor
    failures etc. It might take a half an hour or so to test all the
    electrolytics, but it gives a far lower chance of failure in near
    future.
     
  7. This is the thing I would check first. I had that once: A small copper
    wire coil to the base of the HOT had a faulty solder joint on one
    side. If the HOT is not properly switched (i.e. too long rise and
    fall time of the pulse) it will be thermally overstressed and fail
    prematurely.

    Regards,
    H.
     
  8. Meat Plow

    Meat Plow Guest

    Seems the op says he just replaces the HOT, not HOT section stuff.
     
  9. tem00

    tem00 Guest




    Thanks for the input everyone.

    Yes, it was only the HOT that failed, but the 2nd time it blew I
    replaced a lot of related parts as well in an attempt find a marginal
    part. They were all parts spec'd from Vance Baldwin for my unit and
    seemed to be the same numbers. I used proper mounting and heatsink
    grease. I can test the load current, but it is not specified in the
    service manual so I don't know what to look for.

    I'll use all the suggestions here from the drive waveform to checking
    the copper coil legs and post if I find something.

    Thanks again
    tem00
     
  10. R!

    R! Guest

    <snip>


    I had a set that would do something similar, turned out to be a bad CRT.

    It sometimes arced internally at turn on before the heaters were
    completely heated blowing the H.O.T .

    R!
     
  11. tem00

    tem00 Guest



    Not what I wanted to hear, but thank you, I'll keep an eye on it
     
  12. Meat Plow

    Meat Plow Guest

    This sucks but I recall reading some other HOT failures because of a
    shorted CRT.
     
  13. There's a lot to die before the HOT, if the CRT is bad.

    Regards.
    H.
     
  14. R!

    R! Guest

    Just thinking does the H.O.T. run unusally warm ?

    If not, I read that there was some problems with the sealing of the
    anode connector on some projection sets that would arc, but this should
    be a very audible snap!

    If it is a bad tube it would not be much of a snap.

    R!
     
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