On Sun, 26 Jun 2005 19:40:07 +0200 (CEST), Nomen Nescio
wrote:
On Sun, 26 Jun 2005 11:30:23 -0400, John Bachman
wrote:
Nearly everyone who is into restoring old radios or TV's (myself
included) replace all of the paper caps with polypropylenes or mylars
and all of the electrolytics with new ones. If one of them is still
good, it is likely to fail soon, so why not just replace them all?
There are only three electrolytics in the entire set, one has already been
replaced. The remaining caps are paper, mica, and ceramic. From my
reading up on caps, it's the paper ones that need replacement. Over the
years some of the paper caps have been replaced with orange drops. So I
don't have to do all of them. Still, it's a literal bird's nest of wires
on the underside of the chassis. Seems like back in the 1950's, the way a
TV was designed (or maybe it was just RCA) such that one component wouldn't
short out another, was to simply bend the leads so that nothing touches.
Frightening! The TV may also have transformer problems, although the
flyback looks very clean, with no signs of arcing.
I've read about the ESR meters, just never used one before. And don't
quite understand how it could work with a cap in circuit, as other
components would effect the values of the component under test (like an
inductor in parallel with the capacitor).
First we have to establish that we are talking about two very
different applications: old TV/radio restoration and ESR.
When your TV was designed no one worried much about ESR, it just was
not an important characteristic of capacitors, electrolytic and
otherwise. So ESR measurement is not a big deal in those situations.
I only mentioned it thinking that you might have other applications in
which ESR measurement would be useful.
You are correct in that ESR is affected by other components in the
circuit. Most ESR measurements are made on electrolytic filter
capacitors, not frequency sensitive circuits. In those case, the ESR
can be measured in-circuit as long as the meter does not forward bias
any semiconductors in the circuit. Not a problem with 50's TVs :-)
John
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