I thought it might be something like that.
I have never heard of that being an issue, but I did manage to blow a cap on my Yaesu FT101EX when I turned it on for the first time in well over a decade. Nothing like starting off with a bang...
I wonder if it's still an issue. After all, we no longer have to take extreme precautions when dealing with CMOS circuitry.
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On 01/26/2011 05:08 PM, AlienRelics wrote:
The layer of oxide is not static, it is in a dynamic equilibrium. That is one of the reasons why there will always be a small leakage current. As parts of the oxide lose oxygen atoms and become conductive, a little bit of current forces the aluminum atom to oxidize again.
That is why antique electronics should never be just plugged in and turned on when they've been off for a long time. If you do, then a high leakage current may flow, causing a lot of heat and the caps will fail. Sometimes catastrophically, sometimes the fuse just blows.
We call it "reforming the electrolytes", and we don't mean that we send them to a bootcamp for teenage delinquents. You connect it to a variac (variable power transformer) and start with it at a low voltage and bring it up slowly over a period of days or weeks while monitoring the current draw and temperature of the electrolytic capacitors.
In normal operation, this oxide layer is constantly losing oxygen and then being "reformed" (reoxidized) by the leakage current.
Running an aluminum electrolytic capacitor at well under its rated voltage will cause the oxide layer to not reform correctly and the leakage current may rise. Then the heat can cause pressure that causes leaks around the seals, drying out the electrolyte.
You do need to make sure that the voltage rating is high enough for the peak voltage that the cap will see.
I don't have a link to give you, I learned this long ago. Since most engineers get it drummed into them to save costs and so parts get derated as little as possible, this is more of something that techs learn through experience.
Steve Greenfield AE7HD
