[sdiy] capping

[Steve Ridley]

I can see why recapping causes such mixed opinions. On one side, it makes sense if you know what you're doing overhauling or repairing for a customer, but when it's done "because everyone says you should do it" and the replacement caps are cheap ones with a worst case life of 1000 hours it's can be unnecessary vandalism. Recapping has it's place, but should be done when necessary, not as a random act of maintenance.

Not all caps deteriorate at the same rate. Type, make and position can make a huge difference. A cap next to a hot power device is likely to deteriorate much sooner than an identical cap elsewhere. Certain makes of cap have a poor reputation, but knowing which ones comes with time and experience. One bad cap doesn't mean they'll all be bad. I like to know what's going on before I consider recapping.

Some ESR meters will test caps in circuit. I use a Dick Smith ESR meter, now discontinued, but EVB and Anatek make very similar models. They will give a useful indication of the state of a cap without removing it from the board, although multiple caps in parallel or shorted caps will give a false good reading. 

The other important tools are your eyes and nose - look for staining at the end of the cap. Leaky caps have often have a distinctive acrid fishy smell - a real giveaway.


Steve