My poor iMac

[giza]

When I got back from Dorsai Thing a few weeks back, I saw a kernel panic on my iMac, so I tried rebooting it. Upon rebooting it, the screen stayed black and no sounds came from the speakers, nor did the Caps Lock light turn on on the keyboard when I pressed the key. So I took the machine out of service and made a note to open it up at some point

Comments

[delphanaeous]

I had an Athalon XP board that failed where nearly every capacitor had expanded.... I might still have that board too...

[chefmongoose]

Same thing happened on a video card last month for me. Likely one of those capacitors started going a while ago, and it took three gone before it stopped working.

[thraxarious]

Yep, its not a hard fix if you have a good soldering iron and a spare $20 to digikey. You just have to choose good Cap brands, and not bad ones.

I can't see what brand they are, but they have coloring kind of like Panasonic, but not the tops.

Capacitors can often fail in a block like that, its common. If you want to try, you would be best to replace ALL of those, as when one starts to fail, it will generate excessive heat and cause others nearby it to fail too.

I can see they're 6.3v 1800uf, so that would not be too hard to find. Don't get Radio shack if you do. They're garbage. Definitely you want low ESR caps. Check the size of them, the biggest problem I have found is getting replacements of the same size.

If you are interested in a resurrection project, I would go read up on www.badcaps.net forums. Hell, they often get a lot of people talking about common brands, common failures of models, etc.. not a bad place to see what brands are using cheap and which are not.

[shockwave77598]

Actually, they don't. One or two will blow out and the circuit can still function. By the time you've lost enough that the computer quits, you've got a group gone bad.

[thraxarious]

They can fail without any physical signs of failure. The ESR can go to crap without them bloating or popping. The only way to be sure is to dig them out, and test them with an ESR meter.

Still, its a good idea to just replace them all. One bad one can cause others to die out faster.

Hence, its better to replace them all. When they cost so little to replace, its not a big cost.

[shockwave77598]

Absolutely!! If you are replacing one, replace them all. And with Tantalums if possible to eliminate the drying out problem.

[siege]

Looks like four or five of 'em to me, in that photo. I notice the ends are trimmed so the caps are more likely to blow out that way instead of bursting their sides.

[shockwave77598]

The electrolyte gets hot from the million times a second charge/discharge of a switching power supply. Finally, they are dried out and go foom. Average time to fail - 4 years.

Which is why we don't use them at ALL in avionics. Tantalums pretested to weed out the shorted ones are what we use. Find a place that can replace them and hand the tech some tantalums to go in place and the computer will easily last another decade or two.

Notice how old electronics didn't have this problem? You could find a mid 70s tv and it would still function? Because they weren't given such hard driving jobs like switching power supplies back then. Today, buck convertors to efficiently convert 5V 10A to 1.2V at 41A really push electrolytic caps to the wall.

[thraxarious]

Some of the people doing replacements of Electrolytics do "poly Mods" using solid state polymer capacitors, they have a much longer lifespan and are more resistant to heat. That is why I look over motherboards to see what kind of caps the are using, you can tell the cheap ones from the good ones.