Re: Working on a //+

["Tom Zuchowski" <tzuchow@attglobal.net>]

Paul, your anecdotal response to a general comment is like the lady who
disagreed with the comment that most men are physically stronger than most
women because she can personally bench-press 350 pounds. There is a
statistical bell curve to any general statement. While your caps are still
good after 20 years, somebody else's power supply died when it was just one
year old. Using your anecdotal approach, that person can argue that caps
should be changed at least once per year.

Just because your Apple II still works is absolutely no indication that the
power supply's capacitors are in the pink of health. Which would you think
are more likely to fail in the next six months, your 21-year-old caps, or
brand-new ones? Bearing in mind that switching power supplies are brutal on
capacitor life.

Bell-curve notwithstanding, the caps have a NOMINAL life of about 10 years.
If you are going to all the trouble of opening up the unit, why would you
waste time testing a part that is 13 years past its MBTF and costs $1.29?
Especially when going to this extra effort greatly enhances the odds that
you will have to do it again in a year, when the supply fails again?

I work in the industrial electronics repair business, and all I can tell you
is that our policy is to automatically replace all electrolytics that are
ten years old, and to replace ALL power supply caps regardless of age.
Believe me, we don't do that because we like to blow money and shop time
uselessly.

Tom Z


"Paul Schlyter" <pausch@saaf.se> wrote in message
news:9rs1q3$cmb$1@merope.saaf.se...
>
> On Sat, 22 Sep 2001 07:51:02 -0400, Tom Zuchowski wrote:
>
> > Ralph, don't waste your time testing the capacitors. If they are ten
> > years old, they should be replaced. Heck, for these older caps that
> > we are discussing, they should generally be replaced when they are
> > six years old
>
> You seem overly pessimistic about the lifetime of capacitors....
>
> I'm posting this on a 13-year old PC.  No capacitors were ever changed
> there, and it still works fine.
>
> My own Apple II+ is 21 years old -- its power supply still runs fine
> even though no capacitor was ever changed.  It does have problems
> with oxide at its slots and cards though.
>
> Last summer I bought an old radio at a flea shop.  It was
> manufactured around 1956 -- yes that's 45 years ago!!  I had to fix
> some mechanical stuff to get it working OK, but the electronics
> worked fine -- no capacitor needed to be replaced - it would actually
> be quite hard to find the high-voltage (300 to 400 Volts) capacitors
> needed there: it runs on vacuum tubes, not transistors.  For its time
> it was quite modern - besides the common long, medium and short wave
> bands it also had the FM band (although the "old" FM band which ran
> from 88 to 100 MHz; nowadays the FM band goes all the way to 108 MHz).
> The reason I bought it was pure nostalgia: when I was a little kid
> my parents bought a radio of precisely that model.  I was surprised it
> worked so well - I had expected at least some problems with its
> electronics, but it works just fine.
>
> Thus capacitors need not necessarily be changed after 6, or 10, years;
> some work fine even after 45 years!
>
> --
> ----------------------------------------------------------------
> Paul Schlyter,  Swedish Amateur Astronomer's Society (SAAF)
> Grev Turegatan 40,  S-114 38 Stockholm,  SWEDEN
> e-mail:  pausch at saaf dot se   or    paul.schlyter at ausys dot se
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