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CTC169 voodoo

Discussion in 'Electronic Repair' started by [email protected], Mar 10, 2006.

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  1. Guest

    This thing is f___ing haunted or something. Other person does not
    bevlelv my conclusion either, so I present it to you.

    The ticket says "dead". I plug it in, with my handy scope probe near
    the SMPS transformer an it looks normal. The normal stuttering and then
    normal, well normal for that chassis. I pointed my remote into the
    crack between the lightbox and the top back of the cabinet. The set
    fired up !. I unplugged it, went to check caps in the SMPS, found 350V
    units in there, replaced them. OK , but not the right track.

    When I went to fire it up again, it crackled and shut down. I was
    thinking coolant leak but I now pull the CRT leads from the HVB first.
    This is soon becoming an industry (axiom ?) standard with me. Due to
    the frequency or cracked CRTs and coolant leaks, it is worthy of
    checking into.

    I have scoped the 143 and 15 volt lines during startup, and have
    already replaced both of their rectifiers. I scoped the main, and I
    know sometimes you can't see on the scope, so I clip leaded in a
    470/200. No good.

    Now in this set, standby B+ is only 138 volts. Caps have been changed.
    Both diodes as well. Also the 205064, and it now shuts down even
    disconnected from that.

    I scoped the regulated B+ and it is not getting excessive, We know it's
    not a coolant leak because the CRTs are disconnected, and get me right
    on this, the lead to the focus block has been out as well. Everything
    has been checked independentely.

    Checking the HV is a real bitch in this chassis, but I might just have
    to do it. Pin 5 of the fly is putting out 38V P-P and that is high. If
    you look at the shutdown detector it feeds you can see, and it's also
    almost as high to the actual filaments.

    I am leaning toward a bad fly, but I relly don't want to order one
    unless I'm sure.

    Could this condition be related to the totally FUBAR way they derive
    the 220 and that other source ? Could..................

    I will let this post stand, it got me here. This is what seperates the
    Men from the boys.

    I just figured it out, it it the fly, but a wierd thing, one connection
    is broke. Specifically the connection that grounds the main secondary
    for all the scan supplies. You see it is no longer grounded in the
    proper place, and somehow this double forward/reverse rectifying system
    they got is providing a ground. This means there is a leakage path
    also.

    Not for sure, but that is a floating winding and funny things can
    happen to floating windings.

    Mind you that everything else is normal off the fly. All scan derived
    sources are , well I checked most of them. It is just putting out a 38
    volt pulse on pin 5 instead of like a 28 volt pulse. The pulse width is
    normal.

    Has anyone seen this happen before ? and if so, is it the fly ?

    Thanks for anything.

    JURB
     
  2. Jason D.

    Jason D. Guest

    I'm referring to '169ers.

    This chassis has bit flimsy traces at front edge that could interrupt
    the feedback for the run circuits. I had to fix one, multiple breaks.

    Make sure you have good ground connection to that pin, the metal
    gromment tend to oxide and open up on the PCB.

    Oh yes, fly do and will open for no reason. I had one happen on my
    bench 3 years ago. Running happily one moment, foop! CRTs went out, I
    was there with my co-worker, we freeze and our mouths fell open. Just
    that. B+ and collector pins on fly busted open without outward sign
    of burn or other distress at all. Not even a POP.

    Cheers, Wizard
     
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