Re: Capacitors Question?


toby@...
 

On 2018-03-06 4:25 PM, Chuck Harris wrote:
Not to put too fine a point on my nitpicking, but
AFAIK, the capacitor plague applied only to radial
leaded, low ESR electrolytic capacitors, not to
SMD electrolytic capacitors.

The problem mostly appeared on computer motherboards,
and on graphics cards. The electrolyte would etch
through the factory applied anodize coating, which
was the capacitor's dielectric. When this dielectric
layer was thin enough, the leakage current the capacitor
drew would climb, and the capacitor would get hot.

The heat made the electrolyte boil, and the cap would
blow out its bottom rubber plug, leaving the cap all
akimbo, or it would "dome up" the the explosion relief
on the top, or sides, of the capacitor.
I've seen it on dozens of LCD inverter boards. In my unlearned opinion,
though some specific plagues may have occurred, it's a general problem
due to the cheapest electrolytics ("CapXon" brand stands out) being
built into consumer/office products, simply making them disposable after
a couple of years.

My introduction to the whole issue was when an ex-boss put his very nice
twin Samsung LCDs in the dumpster. I took them home and gave them a new
lease of life with $2 of caps. Fixed dozens more after that.
http://badcaps.net is a useful resource.

--T


-Chuck Harris

Dennis Tillman W7PF wrote:
Hi Michael,

Don't do anything until you read this article which explains the problem in detail:
https://en.wikipedia.org/wiki/Capacitor_plague

Dennis Tillman W7PF


-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Chuck Harris
Sent: Tuesday, March 06, 2018 11:26 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Capacitors Question?

The problem will never really be completely solved, as long as manufacture involves putting a plastic/rubber sealed, liquid filled, component into an oven heated to soldering temperatures as a means soldering its leads to the board. You are heating up a lot of things that don't want to be heated up, just to solder a couple of tiny little tabs to the board. Heat them a little too hot, or a little too long (same thing), and the seal will be damaged, and won't keep the electrolyte inside of the capacitor.


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