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How fix lines on CRT from signal lead ?

Discussion in 'Electronic Repair' started by Jon D, Aug 24, 2006.

  1. Jon D

    Jon D Guest

    My 17 inch CRT sometimes gets ...

    light-colored horizontal lines
    a couple of inches above the bottom of the screen
    usually just one or two of these
    the picture size too *sometimes* seems to get a tiny bit smaller
    when these lines are present.

    I have tracked this down to the signal lead going from PC to monitor.

    This d*mn lead seems quite sensitive because slight kinks and bends
    in the lead can create this effect. So can gently moving the plug as
    it goes into the video card. Why can't they design a better lead
    than this? It is already the most inflexible lead on my whole
    system!

    MY QUESTION IS ... is this lead usually as sensitive as this or is it
    related to the design of my particular monitor and PC interface.

    Can I do anything to improve the situation? I have lowered the
    screen refresh rate a bit but that doesn't seem to have help.

    Is there a "magic bullet" like something to clip onto the leqad or
    some screening.

    Changing the lead means some tricky messing around inside the monitor
    to terminate the leads it in the screened cage sitting on the cathode
    parts of the CRT itself.

    Any ideas?

    Jon


    [Please don't say buy a secondhand 17inch monitor for next to nothing
    because cleaning it and dusting out its internals to sharpen up the
    image and all that stuff takes time, and so does fetching a checking
    over monitors which turn out to be crap.]
     
  2. Rod Speed

    Rod Speed Guest

    They can fail.
    You only get that if its got a break in the wire or at the connector.
    Likely thats where the problem is.
    They can, you dont see that with most CRTs.
    Because its got the most wires in it.
    Nope, most CRTs dont behave like that.
    Not the design, the actual implementation of the cable/connector.
    Yes, replace the cable and connector if you dont get that
    effect with a different CRT. If you do, its the video card.
    Yeah, wont make any difference.
    The problem is a physical break in the cable/connector.
    Yeah, tho you can find that the break is actually in
    the connector itself, or even just a broken pin there.
    Replace it with a 19" CRT.
    Then buy a new one.
     
  3. Or don't do anything at all.. ;)
     
  4. johns

    johns Guest

    You probably have corroded solder connections
    where that pc board hooks to the input cable.
    Very common in old crts. Sounds like you also
    have a flyback going bad. Time for new monitor.

    johns
     
  5. lsmartino

    lsmartino Guest

    johns ha escrito:
    Please explain how a bad flyback can cause the fault described by the
    original poster.
     
  6. johns

    johns Guest

    Picture size .. blooming .. is caused by high
    voltage changing. Generally when the solder
    joints start going, it occurs across all the power
    handling connections, and at the flyback. Also,
    the electrolytics tend to crap out and lose their
    capacitance .. even to dead shorts. I've been
    into lots of crts where all I did was touch up
    solder connections and replace electrolytics
    .... and the thing ran fine. Of course that did not
    fix the gassy crt which starts the picture to
    blur. TRUTH: I've had people come in and say
    "just make it work. I'll pay the cost. I like my
    crt". So, I clean it ... resolder a bunch of
    points .. replace horizontal output transistor
    .... replace flyback ... run tube through phosphor
    restore and degauss ... set flyback focus ..
    dark level ... remove and test all the big
    electrolytics, and replace a bunch of them
    .... replace the the transistor amps and current
    limit resistors on the crt board ... put it back
    together and clean the case and screen to
    nearly new ... and charge the lady 3 hours
    labor at $65 per hour plus parts .. and hope
    to heaven that the 90 day warranty holds :)

    johns
     
  7. Guest

    Sounds like a flyback problem, but it might just be a poor connection
    on the sync pulse line. Prodding should lead you to see where its most
    sensitive, and thus where the probelm is. Typically its cable ends or
    connectors.

    The good news is this fault is likely non-fatal. Having retrace lines
    scattered over the screen doesnt exactly make it look better, but it
    means you can wait to see if it goes bad, and if it does find a monitor
    then.


    NT
     
  8. Rod Speed

    Rod Speed Guest

    Yes, but you havent established that the real reason
    for the picture size changing is because the monitor
    is getting confused by the obvious glitches on the
    cable into changing the screen mode etc.
    Oh bullshit. You only get bad joints where large components are
    soldered onto the pcb and they start to fail due to thermal cycling.
    Utterly mangled all over again. Flybacks fail quite differently.
    No evidence of that in the symptoms the OP mentioned.
    Sure, but that doesnt appear to be the OP's problem
    given that its so sensitive to the video cable.
    Irrelevant to what the OP's symptoms indicate.
     
  9. Rod Speed

    Rod Speed Guest

    Nope, doesnt explain the sensitivity to the video cable.
     
  10. lsmartino

    lsmartino Guest

    Rod Speed ha escrito:

    That´s exactly what I thought. A bad flyback will not worsen or
    improve by "wiggling" the VGA cable of the monitor. In other words, if
    the fault dissapears by wiggling the VGA cable, that rules out the
    flyback and other components of the monitor.
     
  11. lsmartino

    lsmartino Guest

    johns ha escrito:
    True, but high voltage changes can be caused by a number of other
    things, not just the flyback.
    OK, but that can be solved by simply resoldering the faulty joints. No
    need to blame the flyback on that, or to replace it blindly.
    Bad electrolytics in the PSU can be the origin of the high voltage
    changes.
    I don´t understand why do you replace the CRT drivers and the HOT if
    they are OK. I can understand that part about replacing aged
    electrolytics, redoing any stressed solder joints and restoring the
    CRT... but why to replace transistors if they are ok?
     
  12. I've never seen light-colored lines like that caused by a bad monitor
    cable, which usually causes the color to be funny all over the screen
    or change abruptly.
    Buy? They're free.
    How long can cleaning take? Almost every one I've found was very
    clean.

    How does cleaning the inside make the image sharper? There are 1-2
    focus adjustments inside, but it takes just seconds to adjust each one.
     
  13. CBFalconer

    CBFalconer Guest

    Wiggling the flyback can disturb the horizontal sync, which in turn
    disturbs the HV, which in turn affects the picture size.
     
  14. Guest

    because cleaning it and dusting out its internals to sharpen up the
    The admission by the OP of being a troll, in plain sight, and nobody
    noticed!
     
  15. Rod Speed

    Rod Speed Guest

    Nothing to notice except you jumping at bogeymen.
     
  16. Guest

    sorry, I though it was obvious. Wiggling a thick fat cable will wiggle
    the main pcb slightly, which may disturb any poor connection anywhere
    on the board.


    NT
     
  17. Rod Speed

    Rod Speed Guest

    wrote
    Never ever could bullshit its way out of a wet paper bag.
    Not if you only fiddle with the video card end it doesnt.
    Pity the FBT isnt even on that board.
     
  18. johns

    johns Guest

    Because you are in there. It takes bench time $$$$ just to
    open the thing, and so you don't take chances on the HOT,
    flyback, power electrolytics, CRT board adjustments .. esp
    the driver transistors and current limit resistors. All of those
    points "heat cycle" badly, and the solder joints crack. That
    causes any movement of the video cable to wiggle those
    bad joints and glitch the picture in a million ways. A bench
    tech can't spend time diagnosing that stuff. I just shotgun
    all the potentially weak areas and run a bench test for about
    an hour to watch the video cycle. If it works ... start praying
    for 90 days. Otherwise .. MAD BOSS ... mad mad Boss !
    Something else .. all those parts run about $30 total on the
    bill. Stupid not to replace them. More stupid is to repair the
    thing at all, but that is not my option, and some customers
    simply believe in maintaining their hardware.

    johns
     
  19. johns

    johns Guest

    Wiggling the cable wiggles the entire monitor.
    What drives me crazy is to pick up the monitor
    and carry it back to the test bench, and have it
    run perfectly :)

    johns
     
  20. lsmartino

    lsmartino Guest

    johns ha escrito:
    Just resoldering the transistors will suffice. No need to replace them
    blindly.

    I agree, trying to repair a computer monitor from 1994 is a waste of
    money.
     
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