13. Motherboard Repair.
Identifying and Replacing Faulty Capacitors

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Below, I will describe the steps on how to identify and replace faulty capacitors


Cylindrical capacitors

What's great about cylindrical capacitors is that they usually visually show when there is a fault. Visually, a good capacitor has a flat and shiny top, and the side with the pins is not buff. The capacitor is able to be tested with a C meter, but this is not always the case because it is on the motherboard.  Sometimes, althoug very rare, there is no visual indication that the capacitor is lacking it's electrolyte. The only way to know when a capacitor is faulty in this case is to use an oscilloscope and see if it it does it's job or not.

The question remains as to how to know if the capacitor is good, or if there is enough space in order for the circuit to do its job. I have been looking for the answer for some time, and I found that if the capacitor has more than 100 uF, it most likely serves as a part of a filter, and the output should be a stabilized voltage. On the motherboard, there are a few places on where to check this. The first place is on the CPU step down converter. The voltage on the CPU step down converter should be flat and stable, and preferably without any artifacts.


Taking out the capacitor. This is not an easy task because the desktop motherboard has four layers, and the heat from the soldering iron spreads. In this case, it is good to use a de-soldering gun such as the Hakko 808. A de-soldering pump can also be used. In addition, it is possible to de-solder the capacitor using a powerful soldering iron no less than 60 W as well as a solder wick. The first step is to heat the capacitors pin and push it to one side in order for the pin to move out. The same should be done on the other side and so on. This does take some time, but eventually the capacitor will be taken out.

SMD capacitors

The capacitors above are soldered on the surface. SMD stands for Surface Mounted Device. There are a few sizes of SMD's with different capacity sizes.

The small capacitors are in the pF range, and usually cause any trouble.

The ones that are in ten uF and up range sometimes give a trouble. They sometimes give a short circuit.

The bigger capacitors are usually colored black and are in the hundred uF range. They will and most likely be 330 or 470 uF.

The bigger capacitors usually cause problems because they are often next to the CPU where is too hot for them.

Most of the time, capacitors will not show any visual signs of fault. The only visual signs of fault they will show is when there is a short circuit, it will burn with a smoke that emits and will become a dark color.

The tools that help to De-solder SMD capacitors are a soldering station with tweezers.


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