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Help fixing Mitsubishi TV model CK35304

Discussion in 'Electronic Repair' started by [email protected], Jun 18, 2006.

  1. Guest

    Hi guys,
    Need help to repair Mitsubishi console TV model CK35304. (36-inch,
    manuf. date 1994).

    Approx a month ago, when you would turn on the TV each day for the
    first time, the top of the screen would be shrunk down a few inches.
    As TV warmed up, the screen would return to normal. Color and clarity
    of picture has been excellent throughout.

    The other day, turned it on, just get a line thru the middle of the
    tube. So, whatever was going bad, has definitely gone bad. I do not
    have TV repair experience, but I have experience repairing other
    high-voltage items, such as many Tube Guitar Amps, antique radios,
    PC's, and even rebuilt a Video Game monitor once (installed a capacitor
    kit). So I am familiar with the voltages involved.

    I talked with a friend of mine who repairs TV (lives several hours away
    from me...), and while he is hesitate to tell me a lot (he never tells
    the secrets of the trade, so to speak...), he said that this a typical
    problem with Mitsubishi TVs, and that the problem is probably in the
    Vertical output circuit, then said 'maybe 5 capacitors, probably a
    chip, and maybe a fuse'.

    Here are some photos of the boards inside the set:

    (mainboard)
    http://mysite.verizon.net/cowman136/tv1.jpg

    (closeup of area that may be the problem...)
    http://mysite.verizon.net/cowman136/tv2.jpg

    (power supply board)
    http://mysite.verizon.net/cowman136/tv3.jpg

    You guys can tell me whether my friends general advice is accurate or
    not. For starters, I have proceeded assuming his advice was good, and
    did some searches to try to narrow down what I am looking for.

    Doing some Google searches based upon part numbers on the transistors
    that I see on the mainboard (picture "tv2.jpg" above) , I found that
    TA8427K is apparently my Vertical Deflector chip, that C2073 is
    apparently my Vertical Output chip. In this circuit, I see the
    following components (and checked them in-circuit, where noted:
    - fuse (checks good)
    - 15K ohm 3 watt resis. - checks good, approx 14K ohms in circuit
    - 4700uF at 10V cap - did not test
    - 2.7 ohm resistor - good
    - 2700 ohm resis - good
    - red capacitor approx 1 inch size with numbers (2A : 335K S) - value
    unknown, not tested
    - resistor with bands of "yellow - purple - gold - gold" - tests approx
    4 ohms.

    My photo tv1.jpg above highlights this area of the board. I do not see
    any visibly burned components or exploded/leaking caps.

    Assistance is MUCH appreciated. I really need to fix this myself, as
    cash is very tight. I do not mind installing a few "extra" parts,
    shotgun approach is fine. Also, advice as to where is best to buy the
    parts (the IC's, as I probably have the caps & resistors) will be
    appreciated. THANKS.
    BJ
     
  2. Inty XP

    Inty XP Guest

    You have a vertical problem.
    Hantarex ? ;)
    This resistor was good ! (yellow-purple-gold = 4,7 ohm)

    Changing components without measures isn't a good idea.
    Start from changing all electrolytic caps in that zone, then
     
  3. default

    default Guest


    This is the flyback transformer area. If the design has the vertical
    circuits power supplied by the flyback, then your height shrinkage could be
    a premature sign the flyback is breaking down, or there could be a problem
    only in the vertical circuit....changing all capacitors in the vertical
    circuit is a common solution to certical problems, however the flyback xfmr
    in that chassis is common fail\, so its of not it be mentioned.
     
  4. Inty XP

    Inty XP Guest


    MAYBE a blown fuse resistor?
     
  5. Guest

    Hi,

    Thanks to `Inty` and `default` for replies.

    The fuses all check fine, unless I am not seeing all of them. I am
    familiar with fuse-resistors, too.

    Update: I changed the 3 electrolytics in the vertical circuits (100mfd
    at approx 35V), and they did not help. I checked the caps that I
    removed, and all were close to 100mfd (the weakest tested 88 mfd).

    Talked to 2 guys (my original source, and another guy that I know who
    was in the tv sales/service business for many years), and both guys
    believe that 99% likelihood that the problem is defective TA8427K
    vertical deflector chip. Both guys said this part goes bad regularly.
    So I have already unsoldered it, and have ordered a replacement. Cheap
    solution if it works. Less than $8 including postage for a real
    Toshiba chip. Should arrive in a few days. If that does not fix it,
    we'll go from there.

    The only thing that I wonder about, is that my friend asked me to check
    whether there is 24V from pin 6 to ground on TA8427K. Well, I got 0,
    although it was `damn hard` to get a reading in that area of the board
    while the set was operating. It is possible I was not getting good
    contact with my meter. Assuming the 0 is accurate, he says that means
    something else is wrong, although he feels that the chip is probably
    bad also (which he originally said I should replace). So I Look around
    on the board, there is not many components in that area. A diode goes
    directly to pin 6 of TA8427K, and a bunch of other diodes are in the
    immediate area (all diodes checked normal once I removed the TA8427K),
    and of course the 100mfd caps (replaced), and a couple mica caps (very
    unlikely to be defective). There is 1 glass fuse in the area, which is
    good. He asked me to look for small black square boxes, which he says
    would be fuses. There is none of them. I can easily identify the
    components in the area, so I really cannot see any way that I am
    missing a fuse anywhere. This might be a lot easier with a schematic,
    but I doubt at this point it would tell me a whole lot.

    I'll know more once the vertical deflector chip has been replaced.
    Thanks again.
     
  6. Guest

    SOLVED by replacing the TA8427K vertical deflector chip. Good as new.
    Thanks to everyone for their suggestions.
     
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