JVC VCR HR-S4700U DEAD SMPS

[[email protected]]

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

 

[Mark D. Zacharias]

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.

 

[[email protected]]

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'.

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.

 

[anamouse]

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'.

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!).

 

[[email protected]]

Anamouse,

Much thanks for the info. Apparently, it's just 'rare' locally.

 

[Mark D. Zacharias]

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

 

[Clifton T. Sharp Jr.]

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

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.

 

[anamouse]

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.

From my understanding 2-3x the voltage rating is ok.

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

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

 

[Roy J. Tellason]

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.

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.

 

[[email protected]]

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

 

[[email protected]]

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!

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

 

[Mark D. Zacharias]

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.

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!