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David Ashton
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re: Pop goes the capacitor!
David Ashton   9/17/2010 10:18:50 PM
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Ants...I once had ants getting into a 25-way RS232 plug on a modem and causing intermittent shorts. I think it was something to do with the formic acid they make. I ws going to write it up for these columns but I can't remember enough of the details. You should write the above one up in more detail, it's a good story.

Nate Ocean
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re: Pop goes the capacitor!
Nate Ocean   9/17/2010 9:11:22 PM
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But what's to be said of today's poorly designed power supplies? I routinely receive from friends dead LCD TVs or Monitors barely a year or two old. Never has there been a digital problem or an actually LCD panel issue. Chips and panels are made in billion-dollar factories and they make solid stuff. Inevitably the problem will be either in the back-light inverter or in the main switcher power supply. Typically you need little more than a pair of eyes to look for the capacitors with bulging tops. These are always on the low voltage side (+5V, +12V, +18V sections). There they are routinely abused because of an inadequately designed switcher and often these are standard grade caps, instead of the necessary low-ESR grade components. Occasionally just for grins (or because I'm an engineer) I'll measure the defective parts. Typically the measured capacitance is about but a fraction of the original spec'd value. In a few cases the electrolyte had dried up and the part was essentially an open circuit. Back-light inverters are also poorly designed. If the capacitors don't go out (as described above) then it's likely the inverter switching transistors. My theory is that the back-light design has such poor margins, that as the bulbs age they require increasing voltage to run. This over-taxes the inverter circuitry which soon fails. It's ironic that on the shelves of Goodwill you can find a *dead* LCD monitors or TVs that are only a few years old--but shot. Sitting right next to them are quality CRT-based monitors--still working--but now obsolete. Monitors that I've repaired include Dell, HP, and Gateway (my current monitor) and Polaroid, Walmart, and a Samgsung TV (my current TV). The guts are from various OEMs, Benq is inside the HP as I recall. In all cases the sub-assemblies are from China, as are the defective capacitors. The Internet is littered with web sites about bad capacitors and how to make repairs.

Donscoggin
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re: Pop goes the capacitor!
Donscoggin   9/17/2010 8:40:13 PM
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Back in the late 8os' at an Itty Bitty Machine companyon a Mainframe type product , we had large 450k ufarad DC output caps exploding confetti. After months of investigating by a product engineer manager who refused to accept that brown stuff happens; he found thru X rays etc that ants were crawling into into the caps during manufacture in south carolina to have a drink of ethylene glycol and when positioned beween plates correctly caused a short. If the caps had an extra vent plug inside (caused by overzealous manual insertion of the first vent plug )then the secondary would block the initial vent causing the eventual explosion. Talk about root cause analysis!!

John.Donovan
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re: Pop goes the capacitor!
John.Donovan   9/17/2010 7:34:39 PM
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In college I worked in the capacitor lab for a microwave company. They made their own caps and my job was to test them for Q, breakdown voltage, etc. We'd put the caps in a lucite box and crank up the voltage until the puppies exploded. The small ones were so ear shattering that we never had the nerve to try it on a large electrolytic!

old account Frank Eory
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re: Pop goes the capacitor!
old account Frank Eory   9/16/2010 9:19:12 PM
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I remember that back in school, some students struggled with the complex number representation of AC circuit quantities, and the idea that the current in a capacitor was the "imaginary part" of the loop current. There is nothing like an exploding capacitor to convince a student that there is nothing imaginary about that current!

David Ashton
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re: Pop goes the capacitor!
David Ashton   9/15/2010 12:03:05 AM
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I have had a few over the years, but the one described was, let's say, the most public one! I find the results are most spectacular when the cap has a bit of time to build up a good pressure inside, as this one did. These days they tend to put weak points on the top of the can for safety, which diminishes the effect somewhat....spoilsports.....

Mark Wehrmeister
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re: Pop goes the capacitor!
Mark Wehrmeister   9/14/2010 3:58:50 AM
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Exploding capacitors, that brings back memories! I had an electronics teacher in high school that wanted to get in good with the students (or scare the heck out of us) so on the first day of class he reversed the polarity on a capacitor connected to a breadboard and set it on a table in the middle of the room. A few minutes later, Pop! Needless to say all of us figured out much faster ways to make capacitors explode and we created our own "fireworks" shows for months after that.

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