The X-Cap-Files

dwight dkelvey at
Tue Jun 2 17:27:44 CDT 2020

These are directly on the power leads. I generally just cut them off.

From: cctalk <cctalk-bounces at> on behalf of Charles via cctalk <cctalk at>
Sent: Tuesday, June 2, 2020 3:05 PM
To: cctalk digest <cctalk at>; Jon Elson <elson at>
Subject: The X-Cap-Files

Today I was working on a new-to-me VT240 which hadn't been powered up in
a long time (possibly 10 years). Hooked it up to an old 9" B&W CCTV
monitor and everything was running fine for 20 minutes or so - when
suddenly an astonishing amount of acrid whitish-gray smoke started
pouring from the vents =8^ O

So I yanked the power cord out and took the case off. Sure enough, one
if not both of the 0.1 uF X-caps on the line filter had cracked open and
my nose confirmed that was the source of the stench.

Fortunately there is no damage to the PC board or surrounding components
- even the caps don't look toasted, just split. Good thing I was sitting
right there when they failed and could turn the power off immediately.
I've read here and elsewhere about the spectacular failure modes of
these caps, sometimes flames, but this is the first time I ever
experienced it first hand. Maybe it's time for a look inside my VT220? ;)


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