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ctc187 output runs hot

Discussion in 'Electronic Repair' started by techo, Oct 14, 2003.

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  1. techo

    techo Guest

    set came in with a blown horizontal output transistor. you could tell
    it had been running hot. we replaced with an original rca transistor
    (in an original rca bag) all voltages check ok, picture looks great,
    but after 15 minutes the heat sink is super hot. this is a 31" model.
    removed driver transformer and cleaned the lugs and resoldered.
    Still runs hot. replaced the flyback, still runs hot. Anyone have a
    suggestion? thanks
  2. John Del

    John Del Guest

    Subject: ctc187 output runs hot
    Check the emitter resistor (smd), then swap out the horiz driver transformer.

    John Del
    Wolcott, CT

    "Nothing is so opportune for tyrants as a people tired of its liberty."
    Alan Keyes

    (remove S for email reply)
  3. David

    David Guest

    Connections to the hdriver transformer are bad causing distortions on the
    drive waveforms. Simply resoldering is NOT good enough. The transformer
    needs removed and the pins carefully scraped clean of the contamination.

    I would assume you already check things like proper b+ voltages, leaky pin
    diodes, noise on the b+ to the flyback etc.

  4. techo

    techo Guest

    the driver transformer had been removed and lugs cleaned off...still
    have the problem. diodes replaced, voltages seem normal. b+ looks
  5. Franc Zabkar

    Franc Zabkar Guest

    I don't know this set, but I had a similar problem in a monitor which
    I traced to an electrolytic cap connected to the "primary" side of the
    horizontal drive transformer. Also check that there is no ringing in
    the base drive to the HOT, and measure the tuning cap and damper

    - Franc Zabkar
  6. RonKZ650

    RonKZ650 Guest

    You're sure you used the correct part # RCA output? They used a lot of
    different ones. Also check the horiz driver transistor itself. I've had a
    couple sets recently that seemingly worked fine, but would short the output
    after a short time that had a bad driver.
  7. Jason D.

    Jason D. Guest

    Claps claps.

    Hot damn, this rca set I fixed (CTC187) blew HOT again but luckily
    didn't take out more parts. Remembering your comment checked the
    emitter resistor and oh wow, IS open (I think R4306 2.4K 1/10W SMD),
    did run without that. Fixed it once and all 2 days ago, HOT heatsink
    ran cool than usual which is remarkable for me as I was used to see
    toasty heatsinks in RCA stuff.

    Thanks for saving me from long day on this 187 and helps me to bring
    closer to understanding the horizontal stuff.

    Yes, I did replace the transformer driver and did every point for good
    solder connections, replaced B+ capacitor.


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