Tiger Luck wrote:
Chris Hornbeck wrote:
On Wed, 10 Sep 2008 21:23:45 -0700, Tiger Luck
wrote:

The best odds-on bet is that despite everything posted
the cap is reversed. Sorry, but that's the main line.

Not a chance... cap installed correctly and worked for years.

Are you saying that *ONE* capacitor has failed? Not
a series of replacements? The thing's 30 years old - *all*
of the electrolytic cap's are bad now. That's life.

At work we buy 100uF 25 volt caps in bags of 1000 and have so far
installed 2500 in 20 year old gear, mostly Sony. But we also have some
Ampex 2" quad machines built in 1978 with _all_ the orignal
electrolytics and the machines are in cherry condition. 30 years is
not necessarily the end point for caps.


Replace *all* of the electrolytics and move on. They're
*all* bad. Parts are cheap.

I replaced all the electro caps less than two years ago. Amp worked
fine up until
now. Polarity was and is correct. After cap blew today, new
replacement cap over
heated. I shut off power before it blew out.

What do you see with a scope? Something definitely funny going on. Is
the transformer heating up too?




BTW, if your question had been about repeated failures,
the diagnosis would be: the cap got too hot. It got too
hot because it was defective, or it was exposed to too
high a voltage,

I checked voltage across cap terminals with cap out. It read
correctly.

or it was exposed to reverse voltage,

Trust me. Polarity was correct.

or it was cooked by ESR.

Equivalent series resistance? Is that a measure of quality?

Oh yeah, ESR is a big deal.


Caps are no-names, both from the same parts house. hmm...


For little ( 1-4700 uF) caps we were using Panasonic FC series but
after reading some Hydrogenaudio forum posts, I found that the FM
series caps are even lower in ESR, longer llife (2000 vs 1000 hrs at
105 C) and they cost a little less. ($57.54 vs $61 / 1000 for 100uF
25V)


So, for future troubleshooting, eliminate these four
and you'll have only a mystery remaining!



Good fortune,
Chris Hornbeck

Definitely want to hear how this shakes out.

G²