Connect with us

JVC VCR HR-S4700U DEAD SMPS

Discussion in 'Electronic Repair' started by [email protected], Nov 2, 2003.

Scroll to continue with content
  1. Guest

    MY ABILITY
    I can solder and de-solder and use a multimeter but that's about it.
    I can spell 'zener diode'.

    SYMPTOMS
    Power supply 'chirps' when AC cord first plugged in. Quickly
    unplugging and re-plugging(?) AC cord will not elicit 'chirp'.
    Unplugging, leaving for a few minutes, then re-plugging will elicit
    'chirp'. VCR is totally dead at all times. Primary and secondary
    appears to get charged--caps in both have charge--and outputs have some
    voltage (don't know, don't have schematic) when initially plugged in but
    they quickly fall over 1-2 minutes (caps draining?).

    EDUCATED GUESS

    The supply initially comes up but quickly experiences some kind of
    overload tripping a protection circuit and shutting down the supply?

    SO FAR

    I've purchased replacements for most of the caps and will soon
    replace them. Fairly exhaustive web searches turn up some similar
    problems and solutions with this PS but nothing quite the same.
    Pointers much appreciated. Tks.

    Phil
     
  2. You're on the right track with the caps. Pay particular attention to the
    120uF 6.3 volt on the secondary, and the 1uF 250 volt (or so) on the primary
    side.

    Mark Z.
     
  3. Guest

    Thanks for the info. Unfortunately, the 120uF and several others seem
    to be 'rare' according to my two local suppliers so I off a huntin'.
     
  4. anamouse

    anamouse Guest



    120uF is not rare. Check mouser.com or just about anywhere.

    http://www.mouser.com/index.cfm?han...roductid=260434&e_categoryid=3&e_pcodeid=6613

    18 cents for 120uF 25V. You can safely replace capacitors with higher rated
    voltages (but never use lower ratings!).
     
  5. Guest

    Anamouse,

    Much thanks for the info. Apparently, it's just 'rare' locally.
     
  6. I just use 220uF for the 120. Works fine.

    mz



    Thanks for the info. Unfortunately, the 120uF and several others seem to be
    'rare' according to my two local suppliers so I off a huntin'.

    Mark D. Zacharias wrote:

    You're on the right track with the caps. Pay particular attention to the
    120uF 6.3 volt on the secondary, and the 1uF 250 volt (or so) on the primary
    side.

    Mark Z.



    MY ABILITY
    I can solder and de-solder and use a multimeter but that's about it.
    I can spell 'zener diode'.

    SYMPTOMS
    Power supply 'chirps' when AC cord first plugged in. Quickly
    unplugging and re-plugging(?) AC cord will not elicit 'chirp'.
    Unplugging, leaving for a few minutes, then re-plugging will elicit
    'chirp'. VCR is totally dead at all times. Primary and secondary
    appears to get charged--caps in both have charge--and outputs have some
    voltage (don't know, don't have schematic) when initially plugged in but
    they quickly fall over 1-2 minutes (caps draining?).

    EDUCATED GUESS

    The supply initially comes up but quickly experiences some kind of
    overload tripping a protection circuit and shutting down the supply?

    SO FAR

    I've purchased replacements for most of the caps and will soon
    replace them. Fairly exhaustive web searches turn up some similar
    problems and solutions with this PS but nothing quite the same.
    Pointers much appreciated. Tks.

    Phil
     
  7. And not too much higher in voltage, either. Word is that electrolytics
    won't "form" properly if not run within some range of their rated voltage,
    and won't have full capacitance if not properly formed.

    I think the OP specified 6.3V. Not sure if a 25V cap is okay there or not.
     
  8. anamouse

    anamouse Guest

    From my understanding 2-3x the voltage rating is ok.
    A 16V one should work fine, mouser sells those too:

    http://www.mouser.com/index.cfm?han...roductid=323926&e_categoryid=3&e_pcodeid=6613
     
  9. Sure would be. A cap that's used with way less than it's rated voltage
    would "de-form" to the extent of that layer on the one plate getting
    slightly thinner, and giving you a somewhat higher capacitance value as a
    result.

    Replacing new caps generally doesn't involve "forming" as an issue. The
    time you've gotta worry about it is when you're using some that have been
    sitting around for ages. Or equipment that hasn't seen power in ages.

    There was a project in Popular Electronics (?) way back when called "The
    Electrolytic Restorer" or something pretty close to that. I don't remember
    much about it and don't have the issue any more, but the one thing that
    sticks in my mind is a whole long string of neon bulbs across the panel of
    this instrument. I'm guessing that most of the ones you were expecting to
    deal with in those days would've been used in tube gear, anyhow.
     
  10. Guest

    Thanks for all who provided info. Got onto Mouser and found all that I
    was lacking, albeit not at the same voltages. From what you've all been
    saying, I think I'm within the ballpark.


    Needed Ordered

    120uF 6.3V 120uF 16V
    270uF 25V 270uF 40V
    1200uF 16V 1200uF 35V
     
  11. Guest

    Replaced all caps. VCR powered up for about 20mins, all looked good
    then, while rewinding a tape, the fuse blew. Replaced the fuse and it
    blew again immediately. Back to the old drawing board!

     
  12. In addition to the primary switching and control transistors, the secondary
    zeners need to be checked, one may be shorted. Either symptom points to a
    likely regulation problem.

    Mark Z.



    --
    Please reply only to Group. I regret this is necessary. Viruses and spam
    have rendered my regular e-mail address useless.


     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-