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Fuse Blows

Discussion in 'Electronic Repair' started by Ish, Oct 10, 2004.

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  1. Ish

    Ish Guest

    I repaired a circa 1970's tube Panasonic portable tv. There was a
    blown power line 'slo blow' fuse. This set also had the infamous
    "insta-on" feature that kept the tube filaments lit while the set was
    off. I disabled this feature by snipping a diode across the on-off
    switch. The set played fine for about four days then the fuse blew.
    I replaced with another that promptly blew as the set warmed up.

    Any ideas on what could be suddenly drawing too much current/

  2. CJT

    CJT Guest

    There are lots of possibilities. A shorted capacitor. An internal
    short in a tube. Shorted windings in the flyback or power transformers.

    Start by pulling all the tubes (making sure you know where they go)
    and see if the fuse still blows. Then replace the rectifier tube
    (if there is one -- it might have silicon rectifiers). Then add the
    horizontal output tube (typically the biggest tube) and associated
    drive tubes. At some point the fuse will blow and you'll have a
    better idea what section is malfunctioning.
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