rkr
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XFX 8600GT Capacitors Popped

Thu Jun 07, 2012 12:24 pm

Hi,
I have an old PC with an XFX 8600GT which was working fine until about a week ago when I heard a loud pop sound and on opening the case found the GPU capacitor to be popped. My question is can this happen on the Pi?
What are the steps to prevent it (on the Pi and PC also :P). I believe it happened in this case because of excessive dirt. (Haven't cleaned it since I got it)


On a side note, I would like some non-Pi-related advice from the awesome community here. Can the capacitors be replaced on the 8600GT and the card be used again or do I have to buy a new one? What is the common practice among tinkerers.
PS The card wasn't overclocked.

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Thanks. :D

rrmcbeth
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Re: XFX 8600GT Capacitors Popped

Thu Jun 07, 2012 1:28 pm

Electrotic capaicitors "pop" because they are installed in the reverse polarity and build up pressure inside. In a production run this is unusual. Don't loose any sleep.

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RaTTuS
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Re: XFX 8600GT Capacitors Popped

Thu Jun 07, 2012 1:43 pm

they can be replaced
one picture would of been enough really :shock:
I'd go with a new card TBH - £40-50 will get you something a lot better than that one now ... :D
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johnbeetem
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Re: XFX 8600GT Capacitors Popped

Thu Jun 07, 2012 6:37 pm

rrmcbeth wrote:Electrotic capaicitors "pop" because they are installed in the reverse polarity and build up pressure inside. In a production run this is unusual. Don't loose any sleep.
If an electrolytic capacitor is installed backwards you'll find out the first time it's turned on. In rkr's case I would guess that the electrolyte has boiled away over the months because of high temperature. I had this happen with a poorly-designed ADSL modem which ran very hot. Since RasPi runs at a much lower temperature than an x86 CPU or video card GPU, it will most likely be a long time before RasPi electrolytics blow. Putting heat sinks on the RasPi Soc and LAN9512 should extend this time.

Here's a poetically-named Wikipedia page on the subject: http://en.wikipedia.org/wiki/Capacitor_plague. It's the Plague! The Plague!

rkr, you can try replacing the failed capacitors, but they may have caused collateral damage to other components so set your expectations accordingly. You probably want to get high-temperature capacitors.

rkr
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Re: XFX 8600GT Capacitors Popped

Thu Jun 07, 2012 7:16 pm

Dang! I knew it was the temperature issue. (Due to the excessive dust deposition)

Thanks for the advice guys. I'm not gonna replace capacitors as chances are less everything else is okay. Might as well have to replace the GPU.

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reiuyi
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Re: XFX 8600GT Capacitors Popped

Mon Jul 09, 2012 2:44 pm

The temperature surely diminishes the lifetime of such a capacitor, but I also believe they're just really bad quality caps

On my own old 7600, the 1000uF caps exploded a while back. They're the same type as yours (6.3v). I believe it's just a bad choice to use 6.3v caps in a 5v scenario. It's a really really bad design choice just to save that cent. I actually replaced the capacitors on my card because I can no longer get a hold of cheap AGP cards (old computer is old). The caps cost about 40 cents in total (3 new 1000uF 25v ones) and soldering them on took about 5 minutes (through-hole). Anyone with a soldering iron could do the fix.

Gert (I believe) picked a 16v capacitor for the raspberry pi. Hopefully it is a good quality one. Though, in the case of the raspi, it is far away from heat sources and its rated voltage is far above the 5v input. It will not explode for several thousands of operating hours.

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Burngate
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Re: XFX 8600GT Capacitors Popped

Mon Jul 09, 2012 4:35 pm

Just because a cap is rated at a higher voltage doesn't mean it's less stressed.
The voltage it can take depends on the thickness of the aluminium oxide dielectric layer. But that only maintains itself while that voltage is present.
However, thicker dielectric means more surface area required so more aluminum hence larger can. This means more heat can be dissipated, so lower temperature. It's also likely its esr is going to be lower, again leading to lower temp. And lower temperature means less boiling of the electrolyte so longer life.

The chemistry is quite complicated, but sticking to caps with reasonable over-voltage is best advice.

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reiuyi
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Re: XFX 8600GT Capacitors Popped

Mon Jul 09, 2012 4:59 pm

@burngate

Your surface-area and temperature dissipation theory is quite good, I believe

What I was getting at is that the 5v rail of a computer PSU is not known for its stability. It only takes a small burp to jump above 6.3v. Most circuits inside a computer are protected from such overvoltage, though a cap stands no chance and is permanently damaged each time. I must say I've never had issues with ESR. The capacitor I used to replace my bad caps was just a random capacitor from my electronics box. It wasn't really "low ESR" or any of that "high quality" stuff. There's much debate about "low ESR" in the audiophile fora elsewhere on the internet.

Update: for whoever is interested, this is a picture of my old geforce 7600 with three (!) popped 1000uf 6.3v caps (2 at the top right, 1 at the bottom left)
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I tried desoldering them with a desoldering tool. As I expected, lead-free Pb is very difficult to deal with. I eventually just pulled them out destructively with pliers
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The three broken ones were replaced by three 1000uF 25v from my electronics box. They aren't as "good looking" as the solid caps that were on there (if they even were solid caps, who knows), but these ones have never failed me. They're not "LOW ESR", but they work and my old computer can continue doing pointless things all day!
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Dilligaf
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Re: XFX 8600GT Capacitors Popped

Mon Jul 09, 2012 6:06 pm

Although heat and voltage may be contributing factors the real root cause is defective manufacturing. The electrolyte used in manufacturing these caps is not of the quality required for long term survival. I have replaced numerous bulging/leaking caps on various boards and have had 100% success. Although peripheral damage is a possibility odds are if you replace the caps you won't have further problems. If you are going to replace them you may want to consider replacing all of the caps and not just the ones that show damage.

Mike

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