The X-Cap-Files

Charles charlesmorris800 at
Tue Jun 2 17:05:27 CDT 2020

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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