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CTC187 picture too big

Discussion in 'Electronic Repair' started by James Sweet, Aug 15, 2006.

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  1. James Sweet

    James Sweet Guest

    Found a shorted diode in the pincushion circuit, ordered an exact
    replacement part and installed it. Pin is now fine however it appears
    the image is a bit too large, I'm not sure yet how large but when I
    change channels the very edge of the text runs past the edge of the
    screen. Pic looks good other than this fault, nice and bright with good
    color.

    Is there a common cause of this? I almost wonder if the EEPROM got
    slightly corrupted though with everything else working fine I'm worried
    that a fault may still be present so I hesitate to adjust anything.
     
  2. Dani

    Dani Guest

    If you found CR4403 bad, did you check C4407 with a cap checker?
    Check the other big diodes, & blue caps in the area. Also, is the B+
    too high? Dani.
     
  3. James Sweet

    James Sweet Guest


    I checked the capacitor both for value with my multimeter and for
    leakage by charging it up to rated voltage with a variable HV PSU,
    didn't think to check ESR on it though. I'll check the other caps and
    diodes, what should B+ be on this set? 180V?
     
  4. Dani

    Dani Guest

    Standby B+ can be about 145 volts, & about 140 running....approx.
    You didn't say if the pix is too high also...B+ could be too high. I
    don't think the EEPROM is corrupt, but if it's just too wide, & not
    keystoned, it MAY need a tweak. Dani.
     
  5. James Sweet

    James Sweet Guest

    It's pretty hard to tell really, when I get the chance I'll drag the DVD
    player down there so I can put a test pattern on it.
     
  6. Bill S.

    Bill S. Guest

    Don't have schematic handy for this chassis, but a lot of these have
    a set of ceramic caps that form an AC voltage divider across the
    pincushion diodes. Failure of one of the capacitors commonly causes
    diode to overheat, and of course any problems in the pin circuitry
    affects picture size. My guess would be look for open ceramic cap
    connected to the diode that failed.
     
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