Fix your old computer motherboard

The last hardware problem that I faced was corrupted computer motherboard. After a full and detailed review concluded that the problem causing the two bad capacitors.

Replacing a capacitor on a motherboard is a very detailed process and takes a steady hand to achieve. Each capacitor is attached to a motherboard very precisely, using solder. When you replace one, the same precision must be used or you risk permanent damage to your machine.

Before you start work you should consider whether the board is going to be working after you replace the capacitors or whether it is going to need a lot more work and parts which you might not be capable of doing or finding.

Checklist for considering a board

If your board meets any of the following criteria then it will probably not be a good candidate for recapping.

• Component(s) on the board are looking burnt
• Component(s) on the board are detached or missing (even tiny smt components)
• An essential connector such as HSF clip, ram clip(s), ATX connector are damaged.
• Traces on the board are scratched

It is good to know the history of the board. For instance if the board developed badcaps but was taken out of service early then it is a great candidate for recapping. If the board was left for a very long time and the caps have leaked all over the place then the discharge can probably be cleaned up nice. If the board is now dead having shut down one day then if there is nothing burnt some caps probably failed open and the board is still good for repair. If the board died and there was a burning smell or burnt items on the board then there is a possibility that some caps shorted.

If you are given a board to troubleshoot which does not POST, it just blinks the led on the board and the fan twitches, you must be careful that the board is not in a condition which will damage the CPU that you use to test the board. There is a possibility that the VRM chip is damaged because a FET has shorted and therefore Vcore will be too high. The board will be a CPU killer. Better to test Vcore with a multimeter before you attach your CPU to troubleshoot the board. It is always a good idea to test unknown boards with your worst components anyway.

You will need

• Soldering iron
• Cutting pliers
• Gloves
• Safety glasses
• Rosin core solder
• The replacement capacitors
• Anti static band (if your working with delicate circuitry)
• De soldering pump (optional)
• De soldering wick (optional)
• Antistatic Wrist Strap

Clean the board   

Clean the board of dust on both sides using canned air before you start work.

Locate the defective capacitor

The first step in the repair process is to identify the capacitor that needs to be replaced. Typically, a bad capacitor has some manner of bulge on the top of it. Bulges are sometimes very subtle which makes them difficult to detect. Another sure sign that a capacitor is bad, is if it has leaked.

Get your antistatic wrist strap on   

You must wear an antistatic wrist strap when you are soldering or handling the board. Put it on the hand holding the iron. The best place to connect the wrist strap is to the back of a computer which is plugged in.

Remove the damaged capacitor

The junction point for each capacitor is on the bottom of the motherboard, so you need to remove the motherboard to access the underside. Using your soldering iron, heat the existing solder at the junction point for each (usually two total) leg of the capacitor. Then, gently pull the capacitor away from that leg on the top side of the motherboard.

Having Problems to remove the capacitor?   

If you are having problems to remove the capacitor then maybe your iron is not hot enough. If it is a 60W then maybe you should try a different sized tip, perhaps the tip is too long and thin and not transferring enough heat from the iron's heater.

Dont forget that if you are working near big traces they suck up the heat from the iron making it difficult to work in that position.

The types of solder used appear to differ with each board manufacturer. Some are easy to heat up, others are not. Older boards are more difficult to work on. Most boards you will have no problem with if your iron is hot enough.

There are different techniques for working on difficult boards. Some like to heat the board with a hot air heat gun or work with hot air pencil. Others like to use large wattage soldering guns for stubborn solder pads. All of these require some experience and knowledge otherwise the board will get trashed.

Clearing the Hole  

Once you have removed the capacitor the hole will not be clean unless you are quite lucky. Some people dont bother to clean the hole but position the leads of the new cap against the holes and then push the cap in at the same time while heating the holes on the back of the board. This not such a great method and it is best to clean the hole first before installing the new cap.

Here we will discuss some methods for cleaning the holes. Really you will have to find the method which works best for you. In order to clean the hole it may help you to have the board held by the board holder.

Replace the old capacitor

After removing the bad capacitor, you must clean the holes before you can put a new one in place. This is achieved by heating the leftover solder in the holes and using a de soldering pump to remove any excess. When the holes are clean, you can proceed with installing a new capacitor. There is a positive and a negative leg on each capacitor, so you need to make sure you insert the legs through their corresponding holes in the motherboard. The motherboard should have markings to indicate which hole is positive and negative.

Tip: The positive leg, or terminal, is typically a little longer than the negative one.

After you have inserted the capacitor legs into the correct holes, clip off the excess wiring from each leg. Clip them to the length of about two millimeters from the underside of the motherboard. Now you can apply fresh solder at each junction point. You should only need a drop of solder to secure the leg at each junction point. The bad capacitor is now replaced and you can test out the motherboard to see if it works properly again.

Finishing the Job - Cleaning the board   

When you have finshed you will need to clean the flux from around the solder joints and also the flux splatters which may be around the board. You will need to use a FLUX-OFF spray. I am using one from Cramolin which is called FLUX-OFF and is dimethoxymethane. This will damage plastics and PVC so you will spray a little around the solder joints and manipulate the excess using a cotton bud or Q-tip (normally used for cleaning your ears) so it does not flow down a hole like from the PCI slots or whatever to the other side of the board. Then you can rub the excess flux around the joints using the bud. After doing all the joints and checking for ones i have missed i leave the board with a halogen desk lamp (or other hot desk lamp) about a foot from it for 10mins to ensure that all the FLUX-OFF has evaporated. It is highly inflammable so no smoking. The reason you do this cleaning is because some fluxes are mildly corrosive.

Run test utilities   

 First I would start off booting a ram test utility disk like https://www.memtest86.com/ and checking for ram errors for a few hours while using known GOOD ram, then you can run some burn in utilities like prime95 https://www.mersenne.org/freesoft.htm also in Windows and you would want to see the board totally stable with no errors after running them for some days. At least run the board overnight if you are in a hurry.

Good luck with your new board :)