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Nokia VCR3785 showing "sparkles" on tuner-picture

Discussion in 'Electronic Repair' started by Marko Taponen, Jan 25, 2004.

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  1. Hi all,

    I was wondering if anyone could give me a hint or piece of info on following
    matter.

    I have Nokia VCR3785 hifi video's (~6-7 yrs old) and now the tuner picture
    is really poor.
    I mean when I connect th TV to the SCART- outlet of the VCR the picture is
    really poor when looking broadcast and ok when looking cassette.
    I'm connected on cable, and my philips TV (which is btw really sensitive for
    bad transmission) is showing good picture.

    But the VCR-tuner picture shows sparkles. I can change the sparks to
    "grooves" by turning a trimmer on top of the RF box but the picture is still
    not ok. Also if I lower the amt of signal by partially removing the RF-in
    plug from the jack behind the vcr I see normal, snowy picture without these
    sparkles.

    I already soldered the RF box out as I suspected something was
    "oversteering" there but it looks ~ok.

    If someone would know service manual for the device or would have good hints
    or guesses how to get more info on the problem please help.

    Best Regards
    // Marko
     
  2. eddumweer

    eddumweer Guest

    Hi Marko,

    If oversteering is the problem, you can try with one ore more 2 way
    splitters for coax in the rf-input of the vcr. Every splitter gives about
    3.5 dBuV loss in signal.

    I myself check the rf signal from the cablenetwork or aerial with a
    calibrated rf-meter, and depending the rf signal, alignment of the amplifier
    or calling the cablecompanie or using attenuators for getting the right
    signalstrength.

    If the problem is specially of vhf-channels also check the proper grounding
    of connectors, cables because vhf-channels are sensitive for bad grounds
    (shielding)

    Greetings Peter
     
  3. Vector Viper

    Vector Viper Guest

    I have seen similar pictures on older vcrs here in the US...there is a 1 or
    2.2uf
    cap in the i.f. strip that filters the rf AGC, if it goes bad, the pix can
    be unstable, snow, streak,
    pulse, or jump...experiment with briging caps in the i.f. area....

    My first guess...

    Aaron H.
     
  4. Thanks -- I had some other responses indicating the same and I soldered of
    the IF box and replaced all ElCo's inside. This indeed fixed the problem

    Cheers,
    // Marko
     
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