There are really only two components on a motherboard that fail due to old-age: fans and capacitors. Fortunately these are also the two components that are convenient to replace. After a recent spate of motherboard capacitor problems amongst my co-workers, I thought I’d post some useful tips about repairing them.
Symptoms
Unless you are regularly examining your motherboard capacitors the first sign of capacitor failure will usually be boot problems. Often the computer will fail to boot, or will only boot one time in six. In one recent case the symptom was that the computer only booted when the video card was wiggled. There might also be hard lock-ups when the computer is under load (either CPU or video). These can all be signs of power supply problems, in which case it is either the power supply failing or the motherboard power electronics. In either case cheap capacitors are often to blame. I’ll ignore power supply issues; they are often fixable in a similar manner, but screwing up a fix on the power supply is a little more serious than the motherboard and so it should be avoided by most people.
Spotting a bad capacitor
This is surprisingly easy. Look at the top of the electrolytic capacitors, especially the large ones. (If you don’t know what an electrolytic capacitor looks like, your probably shouldn’t try replacing them, but they’re the stubby cylinders, often blue, black or gold, that sit around the CPU.) At the top of the electrolytic capacitor is a disk of uncoloured metal with some score marks across it. If the top is puffed up then the capacitor should be treated as bad and replaced. If it is leaking electrolyte (usually a brown-coloured ooze seeping through cracks where the score marks are) in any quantity at all the capacitor should definitely be replaced.
Choosing replacement capacitors
Now you know what to replace, you have to get replacements. The capacity and voltage should be written on the side of them. These are the principal parameters for capacitors, but not the only ones. It is also desirable to get low-ESR (low effective series resistance) capacitors to improve the quality of the filtering. On top of this, also look at the temperature rating of the capacitor. Typically this is about 80 degrees, but given the loads these capacitors are under going for a higher temperature rating will improve their life-span. Also, try and get good quality capacitors from a reliable manufacturer.
Replacing the capacitors
The first thing to do is note the location and polarity (and also the value if there is more than one type) of each capacitor you want to replace. Most motherboard have several empty sockets for capacitors that aren’t actually used. This can be very confusing once you’ve removed the dud capacitors. If you get caught out this way, look for the holes that have remnants of solder in them.
Secondly, remove them. A good solder-sucker is invaluable here. You may also want to turn the heat up on the soldering iron (say to about 400 degrees) if the capacitors are attached to big ground planes (solid areas on the circuit board) since these are also good heat-sinks (this is no coincidence). Note that you are also likely to be working close to fine tracks, so be careful not to damage them or splash solder in a place that might short out some tracks. If, once you have removed the capacitor, there is still solder in the hole you might try refilling it with solder and using the solder-sucker again. Without the leads of the capacitor in the way it usually clears nicely.
Finally put the new capacitors in. Make sure they are the right way around! You should have noted this earlier, but fortunately a lot of motherboards also have the polarity marked on the top side. It is possible that the replacement capacitors are a slightly different size and they won’t all fit. In this case your only real option is to find another set of replacements. Soldering should be done carefully, just like the desoldering. A high temperature may still be useful. As always you want to take enough time to get a good join, but no more. If you had to remove the CPU to get at the capacitors, put more thermal paste between it and the heat-sink when you replace it – you won’t regret doing this.
With luck the motherboard should boot now. Of course it could have been something completely different that has failed and you may be back at square one (with the added suspicion that you botched the job and broke the motherboard) so isolating the cause as much as possible before-hand is highly recommended. Even so, bulging or leaking capacitors are at best a failure waiting to happen. Conversely, don’t replace capacitors that aren’t bulging unless you have the means to test them and determine that they really are bad.