Archive for October 20th, 2005

Capacitors suck

There’s an old adage in the electronics world, dating back to the glory years of vacuum tubes, that goes “only capacitors and resistors can go bad… and resistors never fail on their own.” It’s still as true today as it was then… perhaps more so.

Capacitor technology has improved remarkably since the days of paper-and-wax capacitors. However, even good electrolytic capacitors today are one of the weakest components of any electronic system, and a huge volume of cheap, off-brand caps from Asia are anything but good. A lot of people are familiar with the bad caps found on computer motherboards and in power supplies, which lead to erratic performance and premature failure.

I recently encountered an entirely different situation, but just as easily rectified. Several years ago I got an old 12V, 4.2A power supply on eBay for a couple of bucks. I used it off and on for testing this and that, generally non-critical things like fans, CCFL inverters, and so on. A few months ago, I tried to connect it to a 2-meter ham radio transciever. The results were less than spectacular; recieve audio was really poor, with all sorts of noise, and the squelch had to be turned nearly all the way up to silence steady noise on all channels. The power supply was, according to it’s markings, made in 1984, either March or October, and is a switch-mode (SMPS) supply, so I initially chalked the problems up to it just being an old, poorly-designed power supply. Curious if the noise from the power supply was audible on transmit, I keyed the mic, and was rewarded with a sizzling sound coming from the power supply.

Not surprisingly for a twenty-year-old power supply, the output filter caps – all ten of them – had failed. Thankfully, they hadn’t failed by exploding or catching fire, but just by leaking electrolyte all over the circuit board. Setting the stinky mess aside, I turned my attention to the beefy linear power supply I was building, and kind of forgot about the little SMPS.

The other day I came across it, while cleaning, and decided to see if I could resurrect it. I fired up the soldering iron, and replaced all ten (470uf, 35v) electrolytic capacitors with new, identically-spec’d ones from Nichicon.

The result? One perfectly-working twelve-volt supply, with no noise, no hum… working basically as good as it did when it was new, twenty-one years ago. (Yes, it’s old enough to drink!)

The cost for a new, 4 or 5 ampere, 12-volt supply, today? $50-$80, or more. The cost for ten replacement capacitors? About four bucks. Not a bad deal, in other words. If not abused, it could easily last another twenty years before needing a new set of capacitors.

I’d guess that the majority of modern consumer electronics devices that are discarded these days are attributable to component failure… either resistors or capacitors, and resistors still don’t fail on their own. Learn a little bit about electronics, get a soldering iron and some decent-quality parts, and you can save yourself a small fortune over a couple years, resuscitating perfectly good electronics with perfectly awful capacitors in them…

Published in: Geekiness, General | on October 20th, 2005 | Comments Off on Capacitors suck