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Sony KV27S15 died

Discussion in 'Electronic Repair' started by Wayne Tiffany, Jan 28, 2008.

  1. My daughter was watching our TV when she said it made a couple clicks like
    when you turn it off and off it went, not to come back on again. I was out
    of town but had them try the obvious stuff like plug into another outlet,
    etc.

    When I got home I tried a few things, and found the fuse fine & that
    plugging in the set did draw a little current, although there was no
    response at all from the on button. I wondered if maybe the micro was
    getting confused by high ESR caps around it, but found none that appeared to
    be bad.

    I searched for this problem and found some people saying to just change out
    the PS switchers Q601 & Q602 and R607. Some suggested also changing the
    HOT. I checked all solder joints under the microscope and found no bad
    ones.

    From your experience, what would you suggest? I prefer to change parts on
    purpose rather than shotgun, but without a schematic, I'm not sure what
    voltages I should be seeing before the set powers up. At this point I'm
    presuming the power supply quit, but would like some opinions from those
    that know more about this than I do.

    WT
     
  2. James Sweet

    James Sweet Guest

    Is this one of the sets with the separate vertically mounted power supply
    board?
     
  3. Typical repair is the HOT, switchers, and the .1 ohm resistor near the
    switchers, and resoldering the horizontal drive transformer and related
    parts to prevent recurrence.

    YMMV.

    Mark Z.
     
  4. No, the power supply is on the main board. It does have some stand-up
    boards, but they are the tuner & the micro boards.

    WT
     
  5. Typical for these symptoms enough to just order the parts and do it? It
    would make some sense to replace them even if that's not the problem this
    time in that they may be a common failure anyway.

    WT
     
  6. James Sweet

    James Sweet Guest


    Ok I can't provide any specific help on this one then. I fixed a set years
    ago with the separate power supply, on those there's a regulator IC that
    fails.
     
  7. The repair should really be done by a technician or at least by someone with
    some technical ability - there are potential pitfalls in the process of
    replacing the parts, and there are also safety issues, and I have no idea of
    your soldering ability, etc. The 2SC4834 switcher transistors are easily
    reversed, for example - we had a tech do this once. There are numerous fake
    transistors in "kits" out there which aren't really suitable. The horizontal
    drive transformer should be resoldered along with other parts in the area,
    and also the vertical output IC and 9 volt regulator should be resoldered as
    well. Obviously the transistors etc might not even be your problem, though I
    would say it's better than an 80% chance.

    You can get the parts from B & D Enterprises.

    800-458-6053.

    You'll need to order a 2SC4927, 2 each 2SC4834, and the 0.1 ohm Micron
    resistor, they do have high quality kits of these. Beware of kits from
    anyone else.\


    Mark Z.
     
  8. Great, thanks.

    WT
     
  9. Good luck with that. Be careful, and do report back and let us know.

    Mark Z.
     
  10. I talked with Bud there at B & D and the resistor he has in that "kit" is a
    1/2 watt. The numbers that are on the resistor on my board that is labeled
    R607 were 2w.1, which would make me think that it's a 2 watt. He measured
    the one he had and it's 4.5mm dia, and 11mm long. I'm at work and my board
    is at home so I can't measure mine.

    So, the resistor in the kit is the one that is normally replaced. Is that
    R607, or is there another one that should be replaced?

    WT
     
  11. We use the .1 from B & D all the time - it's the same as the Sony, except
    you have to form the leads.

    Mark Z.
     
  12. According to Sony it is .5W. We have used .5W for years and never had a
    failure without a short in the set. I would assume that B&D is selling only
    premium parts, but verify that the transistors are N or P rank or better.
    Lower rank versions are likely to run hotter and vary more. Be sure to
    check the related caps in the circuit.

    Leonard
     
  13. Thanks to both of you - it sounds like I have the correct parts coming.
    Hopefully I will have it running this weekend. I'll let you know.

    WT
     
  14. Well, now I'm really depressed.

    I received the kit with the switchers, HOT, and the .1 ohm resistor. Put
    them in today, and no difference. I checked the old ones and they were all
    bad, so I figured this was going to do it. Plugged it in, hit the power
    button and nothing. Tried it with the front buttonand the remote - nothing.
    No clicks or anything. When I plug it in I can tell there is a bit of
    current draw, but then no indication of activity.

    Any more thoughts of what I can check without the schematics and more
    experience?

    WT
     
  15. Forgot to mention that I resoldered the transformers, etc. None looked bad
    under the microscope, but I did them anyway.

    WT
     
  16. James Sweet

    James Sweet Guest

    Did you create a solder bridge somewhere? Are you sure you didn't leave a
    connector unplugged? Check to see if standby voltage is present.
     
  17. Ditto on the connectors - some models the front circuit board unplugs from
    the main board when you slide the main board out.

    Mark Z.
     
  18. Also it's easy to forget to plug in the power supply main connector to the
    main board, if this is the model I'm thinking of.

    Mark Z.
     
  19. WT

    WT Guest

    I had checked all the connectors about 10 times. There are some open
    connectors on the vertical boards, but I'm out of cables to plug into
    them. :)

    I had checked for solder bridges and found none. All the stuff I
    resoldered was big pads, so a bridge was also less likely.

    The cable from the front board with the switches was unplugged to get
    the main board out. But I checked again and it's plugged in.

    I get about 3.7 vdc on some of the pins of the connector from the
    front panel, and pin 5 goes to .2 vdc when I push the power button on
    the front.

    There isn't a main power connector other than the 110 v line. The
    power supply is on the main board.

    I searched for a datasheet on the micro, Sony CXP80424-079S, but
    couldn't find one, so I don't know what pins should be supply voltage,
    and what pins should change with the power button, etc.

    WT
     
  20. Ok, I finally had a chance to work on this again. I also now have the
    schematics so I have more info at hand.

    I measured my way up through T605, R636 & D619. Measured to chassis ground
    I got 9 vac in front of the diode and 13.35 vdc after the diode, which is
    labeled STANDBY-RECT. This line on the schematic is labeled as 14V so
    standby voltage is fairly close.

    I then followed that standby line to the M board and found the standby 5V
    line out of the M board at the connector that goes to the front control
    panel. I measured 4.25 v at that point. I then checked the power switch
    pin at that connector, and with the button pushed, that pin went to about .2
    v, so I know the switch is closing.

    At D607 which is labeled SOFT-START, which connects to one side of the
    primary coil of T603, I don't get anything, which means that T603 isn't
    running, which means the switchers are not running. (Unless I just have it
    all wrong, which is a possibility.) I see several items labeled
    SOFT-START - what is that functionality?

    So now I'm stuck due to lack of experience - I can't figure out what to
    check next. I see a Q604 POWER-SW and measured 12.8 v at the collector, but
    the schematic looks like it says that should be 0.2 v.

    Thoughts? If anyone would like to call to offer some suggestions, I am home
    tonight. The area code here is 816, and the rest of the number is 796-9886.
    (I don't want the number harvested.) Thanks.

    WT
     
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