I got chronic and acute backwards. It is late here.
On Sun, 20 Jan 2013 00:12:10 -0600, David <davidwhess@...>
wrote:
I have seen two common types of aluminum electrolytic capacitor wear
out syndromes which could be considered chronic versus acute.
The chronic case involves a high ripple current application where the
increase in equivalent series resistance causes the capacitor
dissipation and temperature to rise which causes it to fail even
faster in a positive feedback loop. Circuit failure will often be
because of just one capacitor. Series connected DC balancing
capacitors in half bridge designs are particularly susceptible to
this. The resonating capacitor in the Tektronix designs would be if
it were electrolytic. I try to derate the replacement as much as
possible for longer life.
The acute case involves a whole bunch of significantly derated
capacitors of the same age which just slowly dry out. Circuit
operation becomes more erratic over time. In this case, I find all of
the similar capacitors and change them all. Testing usually shows
that they all have a fraction of their rate capacitance and several
times their rated dissipation factor instead of being completely open.
David Hess