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Mitsubishi VS-50703 Need Advise

Discussion in 'Electronic Repair' started by chaseme5, Feb 3, 2005.

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  1. chaseme5

    chaseme5 Guest

    My tv does not power up. I was looking at the main board on the mitsubishi
    VS 50703 and noticed that I saw clear fluid on the board. An aluminium
    heat sink is corroiding due to the fluid. Is this what happens when a
    eletrolitic cap fails, they leak fulid? Can this damage other parts. What
    do I use to clean the fluid off the board. And what is the best way to
    tell which part the fulid came from if none of the parts look damaged?
    Should I replace all the parts in the area?
     
  2. JURB6006

    JURB6006 Guest

    That's coolant from the CRTs.

    It's bad news, but usually can be fixed. After you clean the PC boards and got
    it up and running you need to devise some sort of gutter. The leak is so slow
    and hard to detect that most of us have decided not to actually fix the leak.
    It is slow enough that it'll be hard to find, and you can't get new gaskets for
    it. Iv'e also seen brand new CRTs from Mits leak within a month so that won't
    do you any good either.

    I'm hooked up with a seal and gasket company and hopefully this year we will
    start selling seal kits. These will be of a special low durometer silicone and
    should never leak. Right now I'm trying to gather up a bunch of these seals so
    they can be measured.

    There might be a little money in it, because you gotta fix the RCAs because it
    screws up the anode cap, and the Mitses will eventually leak too low for proper
    operation. Right now however, the best solution is a gutter IMO. A couple of
    manufacturers actually did use gutters. Mits actually did in the past for a few
    years and NEC also.

    The only problem with a gutter is that the lead dress will never be the same.
    It looks a little messy, but it works.

    The set you got isn't so bad on caps leaking, but they do get high ESR.

    You should probably repost and ask advice on the best way to clean the board.
    My method is a paintbrush among other things with acetone, alcohol and then
    water. After that dry it with a hair dryer. If in doubt, repeat. Sometimes I
    also freeze it with freeze spray to make the PCB contract and squeeze more of
    the crap up to the surface and clean it somemore.

    Wherever it was the worst, take an ohmmeter, preferably one that'll measure up
    to 20 megohms, and stick the probes right on the PCB about 1 mm. or less apart.
    It should read infinity. If it reads any conductance, clean it more or it'll
    get worse.

    Inspect both boards, and be very very careful with the signal board, it's
    double sided and easy to break the feedthroughs. Then it gets very hard to fix.

    I don't care if you got deep pockets and decide to change all three tubes you
    still need the gutter. You DO NOT want this to happen again.

    JURB
     
  3. These tubes usually leak a little then stop leaking. Mostly when the sets
    have been moved. I have never seen one continue to leak enough to run low
    on coolant. We have a technique for guttering them that is easy and does
    not affect wire dress at all. Simply take a short length of outside corner
    molding, wire tie it to the two mounting screws for the frame of the tubes
    and make a vertical gutter to the front of the set between the main chassis
    and the CRT boards. All you have to do is get under the area between the
    green and blue and green and red tubes where it drips off. Takes two pieces
    of molding about a foot long, two nylon wire ties, and upsets no wire dress.

    As for the boards, if the coolant got to the micro, you are likely screwed.
    Otherwise, look for feed-throughs (dual sided board) that are corroded and
    repair any damaged traces before bothering to troubleshoot it. The board
    and the micro are no longer available because of coolant leaks. We use
    isopropanol or denatured alcohol to clean the boards.

    I wouldn't bother trying to market seals for these. Anyone who fixes many of
    them would not bother. If you reseal them after cleaning carefully with a
    thin layer of silicone sealer and let it cure overnight before refilling it,
    they never leak again. Mostly we don't bother if they are not continuing to
    leak. Just gutter it.

    It is ironic that shortly after they stopped putting gutters in the sets we
    started seeing leaks. I can't remember ever seeing coolant in one of the
    old catches they used. They have resumed using them as of a couple of years
    ago.

    Leonard
     
  4. chaseme5

    chaseme5 Guest

    Thank you all for replying, I have a few more questions. Can the coolant be
    refilled in the projector lamps? And How would that be done? Where does
    the coolant usually leak from? What part of the projector lamp? Is using a
    gutter the only solution?
    The fluid leaks on the main board, I found a part that was so corroded by
    the coolant that one of the leads was broken off. Part L932 Coil RF
    10mH-k.
    Do you think this is the cause for the tv not to turn on or do you think
    the coolant could have damaged more parts. Should I replace every part
    that has coolant on it?
     
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