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Discussion in 'Electronic Repair' started by TS, Dec 2, 2006.

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  1. TS

    TS Guest

    I have 27 inches Sony TV, model KV-27S15. The TV set went dead after I
    heard a pop sound .
    Open the back of the TV and visual inspect I found the body of resistor R607
    (0.1 OHM, 1/2 Watt) was burned.
    Inspect the main fuse, it is good. After troubleshooting and repalcing all
    components listed below I restored the normal operation to the TV.

    Q601 = 2SC4834 (Switching power transistor)
    Q602 = 2SC4834 (Switching power transistor)
    Q591= 2SC4927 (TV Horizontal defection output)
    R607= 0.1 OHM, 1/2 Watt

    But the TV works as normal for only 15 minutes then I heard the pop sound
    again and the TV went DEAD.
    I replaced four components above again and the TV now only runs as normal
    for 10 minutes and I heard the pop sound
    the TV now is DEAD.

    I need some help to find the cause of this problem.
  2. David Naylor

    David Naylor Guest

    yes replace ic 600 , with all the other componats you replaced that
    ic is a rugulator usually it blow a hole in itself and lets the smoke
    out, when you let all the smoke out the ic will not work HA HA
  3. James Sweet

    James Sweet Guest

    If that IC were damaged wouldn't the set not work at all?

    I've heard of some Sony sets with similar symtoms that were very picky
    about the parts you use. Try ordering the components straight from Sony,
    also monitor the temperature in operation, if the HOT is getting more
    than warm to the touch something is still wrong.
  4. Art

    Art Guest

    Reflow the solder at the LOPT and Line Driver xfrm, the Horiz output and
    Horiz driver, also check the elect cap in the collector circuit of the Horiz
    driver. Seen a lot of these chassis with atrocious soldering in the Line
    Output circuitry, drops the h-drive, blows the horiz output device and then
    parts in the power supply.
  5. Art is dead on here. These are very routine repairs, usually caused by bad
    solder joints on the H-drive transformer, cusing the HOT to short, taking
    out the PS regulators. Replace the parts listed, look over the caps related
    to the two PS transistors for cracks very carefully, and make sure you get
    good quality parts from a reputable vendor. Use only P rank 2SC4834
    transistors. You can get them from TriTronics, B&D or Acme. If anyone
    tells you that you need to buy the parts from Sony, don't bother, as long as
    you use one of the quality suppliers listed above. We replace the HOT with
    a 2SD1881 because extensive testing showed that it runs cooler and quieter
    than the original and have had a perfect reliability record for us. Just be
    sure to go through the drive circuit carefully as Art suggested. We match
    the power supply transistors for gain and junction bias voltages because we
    buy them in quantities, but this is not realy necessary if you get the P
    rank transistors. Actually the N rank or better will be fine in most cases.

    There have been a few cases of sets with bad flybacks that can eat these
    parts repeatedly, but they are relatively rare. We have repaired this
    scenario many time as described.

    Some techs will tell you to routinely change the VDRs as well. They should
    be checked for shorts, but when the failure is due to HOT shorting, the VDRs
    are always fine. In cases where the PS fails on its own or due to external
    causes, the VDRs are always suspect, as are the caps on the switching
    transistors in the PS and the convertor.

    It is a good idea to brign the PS up slowly on a variac and watch the
    switching for 50% duty cycle and better than 50kHz operation as it begins to
    run. If these two conditions are not met there is more troubleshooting to
    do and the PS will likely blow if powered up fully.

  6. TS

    TS Guest

    Thanks for the tips. I will let you know if I find something.
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