[Test-Equipment] Exploding capacitors ? (wavetek 114s)

[J. Forster]

Cmos wrote:

> Hi all,
>
> Was just looking at a Wavetek 114s sweep genorator. I had taken the cover off
> and was testing
> the different outputs to see if I could get any output on anything, was not
> getting anything. Then,  with out worning(smoke or otherwise), BANG... and a
> cloud of smoke.
>
> A sealed plastic electrolitic cap.(2,000mf) about 1" round and 3" long,
> literly exploded. Shards of plastic flow all over the room, lukely I was not
> wonded, as my face was only a foot from it.
>
> Has any one else experenced this?

Yes. See the photo section here:

http://www.trackpads.com/webs/wireless-set-no19/index.htm

> Ok, now to the point of this email. Why did it explode ? This was a filter
> cap. in the power supply. ....

The most probable reason is the equipment had not been used in a long time and
the cap had gotten flaky. When power was re-applied from a low impedance source,
the heat generated by the leakagevcurrent flowing through the cap caused it to
heat up and make steam. The thing popped because of the steam pressure.

The moral is reform caps that have sat a long time (or replace them). Even caps
that have sat idle for 60 years can often be rejuvenated.

-John