General: Swollen Capacitors

My dad sent me an e-mail today about a digital receiver box that had gone tits up on him. However, he had remembered that I had repaired several devices my merely snooping around for swollen capacitors and replacing them.

If you have an intermittent fault with a device, rebooting, crashing, or turning on then off again, chances are - it's a dodgy, leaky capacitor. It's quite easy to tell when a capacitor is swollen, as instead of having a flat top, it will be convex. The harder ones to spot are when the bottom of the capacitor is swollen, or leaking.

I'm not particularly skilled at soldering or electronics, but I know enough to fiddle around, fix a few thing and do some minor modifications. The reason my dad had e-mailed me, was to see if I had any spare 35V 470uF capacitors. The short answer was no, but in googling around, I discovered that in fact the voltage is the maximum voltage it can operate at, rather than a recommended voltage. This means he could happily replace his 35v capacitor with a 50v capacitor should he have one lying around. In most cases, where capacitors are simply smoothing things out, the same also applies for the capacitance rating, where as long as it is equal or greater than the previous capacitor, you'll be fine. What was probably more important, was matching the temperature rating and tolerance, things he hadn't considered.

I managed to hunt out this article, that I remember seeing a few years back, showing how replacing capacitors on a motherboard revived it from the dead. Expensive motherboards now use solid state capacitors and are much less prone to this problem, but a lot of manufacturers aren't so picky.

Being in the mood for repair, I remembered the two broken 17" TFTs lying in the corner of my room. One of them has an annoying intermittent fault where it will quite happily work for days and then just stop working entirely. It was still under warranty, but when I sent it back, they couldn't find a fault and just sent it back to me - as I was given it broken and other events took precedence - I didn't chase this up. I've now connected this to a machine, waiting for it to go wrong again - so I can have a poke around and possibly fix it.

The other monitor, annoyingly was working fine, until I went to sell it where it decided to stop working (Sod's Law). It now attempts to switch on and off in repetition every second, with an associated click that I'm struggling to pin point.. Unless anyone has any ideas, I'm probably going to scrap it. I had a good tip a while back that the toroid coils can develop dry joints, which revived an old display - unfortunately didn't help in this case.

Are there set specifications for capacitors? Obviously they're going to be different for different voltages right? But are they generally measured in the charge they store, so mAh. In which case it'd be easy to just replace a swollen or leaking capacitor with another one of the same voltage and mAh.

What about strange noises that capacitators make sometimes? Does that indicate, that they will fail soon or that they are already leaking?
I have a PSU that starts with a sqeezy sound each time I plug the connector in and I suspect the capacitators. It works fine with that noise and after more than 2 years I don't expect it to fail, but I don't want to find out what will be burnt when it happens.

Oh, and I have a problem with another PSU:

Each time I plug the connector in, an electric spark occurs. That spark is so strong, that the metal pin tip of the power connector has melted (I'll make a photo). I tried to use a multi-connector with a swich, but I've already toasted two switches within three years. What drains so much power, when the completely shut-off PC (with all the peripherals shut off, too) is plugged in ? This can't be the capacitators of the PSU powering up, can they?

Spode - is there any reason why you have an open bold tag as [b[ ?

He's got plenty to do that he should be doing but isn't at the moment, so he doesn't need you to give him things to do!

UncleNB, it sounds like the wiring in your place is a rather nasty accident waiting to happen! I think Lolly was meaning that the grounding problem was probably in the PSU. Plugging a faulty device in to a properly grounded socket/supply should blow the fuse/circuit breaker.

Please be very careful and if an appliance is using a ground wire, make sure it is in a properly, fully wired socket, including the wiring in the main supply board.

I'm fairly sure your in the US uncleNB, that means most of you supply will be 110 volts. Not as lethal as our 240 volt system, but as larger currents are drawn this can be a real fire hazard and it could under the right conditions kill or maim you.

I cannot stress enough the dangers of faulty wiring in your home, PLEASE BE CAREFUL! I also suggest getting the wiring renewed as soon as you can. We hate loosing members of Spode's abode for any reason.

Not yet, and I hope we never do, especially due to avoidable accidents.

Some American friends of mine complain constantly about the enormous UK plug and its stupid extra pin, but it's the safest power connector there is and it saves lives.