Reforming capacitors (technical description, not politics)

[drlegendre .]

Hi Eric,

Excellent article.

On Wed, Jul 29, 2015 at 2:34 AM, Eric Smith <spacewar at gmail.com> wrote:

> Some people seem to think that "reforming" an aluminum electrolytic
> capacitor is some kind of cheat, akin to zapping NiCd cells or
> rejuvenating CRTs.
>

(...)


>
> The reforming process WILL NOT fix other things that may go wrong with
> the capacitor, such as failed seals allowing the electrolyte to dry
> out, or corrosion, or punch through which can result if the oxide
> layer is degraded and voltage is applied without current-limiting.
>

And therein lies the rub. It seems that so many of the 'legacy' caps we
come across already have some degree of irreversible damage, that the idea
of reforming them appears to be some type of dark art.

Most of my experience in the area is from working with vintage vacuum tube
gear, virtually all of which uses one or more FP-style cans - so the
working voltages are typically much higher than would be seen in older
computer equipment or other solid-state chassis. In this sense, my
experience may differ from that of the average cctalk reader -  but even
the low-voltage (=< 63V) caps I encounter seems to fare rather poorly.

To pull a number from the air, I'd guess that fewer than 30% of the caps
that show up with symptoms are ever capable of being returned to service -
and that may be optimistic.