Sunday, March 23, 2014

The risks of do-it-yourself bad capacitors replacement

We usually refrain from advertising repair services for boards well known for solely developing bad electrolytic capacitors for the simple reason that we believe in the human nature and the ability to do most simple things like replacing them without external help.

Every now and then, though, I am reminded that what may seem very simple and easy to some may not be so easy and simple to others.

(The last time I was reminded of that, by the way, was just the other day when I was asked over $400 for an installation of a simple reverse osmosis filtration system for drinking water under the kitchen heat sink; that was the cost of the labor only , for about 90 minutes of work. Geez!)

Anyhow, while electrolytic capacitor replacement can be considered as easy as component level repair can be, there are some gotchas to watch for.

One thing I've seen in the past is damaging the copper track on the back, front or inside the hole where the leg of the capacitor goes. On some boards there are tracks on both the top and the bottom of the hole and the hole's internal wall is also galvanized and uses as a normal electrical link between the top and the bottom track. Overheating the solder at the bottom and especially under-heating it and ripping out the capacitor would often tear off the galvanized internal layer and when a new capacitor is installed it may not have connection - and if it does it will definitely not be a reliable one - between the top and the bottom track.

I have seen customers and even technicians send boards to us which are otherwise functional, but do not work because of a torn link between top and bottom layer when pulling out a component.

Of course this can happen with any other type of component, not just capacitors.

Here is something, however, which happens in particular with electrolytic capacitors replaced with ones of lower breakdown voltage:

The board in this picture is PS-507-PHN  / LJ92-01513A, but the same could happen with any other board where electrolytic capacitors are replaced with ones of lower breakdown voltage.

The traditional way of blowing an electrolytic capacitor is to reverse its polarity, switching the positive and negative legs. It's very easy to do and sure enough even we do it sometimes.
When put to work, the cap starts heating up quickly and the top swallows.

The capacitors on this board were properly aligned, though, but severely under-rated.
Original ones were for 50V and they were replaced with ones for 16V.
It must have been a loud and smoky explosion and as you can see this poor guy's internals are all over the place.

This picture is just a reminder that when you pull out a board for service it is also in your own best interest to give it a little cleaning.

When the capacitor has exploded part of the foil from its outer body has wrapped itself around a nearby diode. This may actually result in a shortage and needs to be removed.
Other than that and the mess exploded electrolytic capacitors are actually not much harm for the circuits.


Anonymous said...

whats the original Volts and UF of the four that are blown

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