December 8, 2010

Replacing Capacitors in a Motherboard.

     Last year I was given two computers. One of them worked fine but the other one started POST then splashed an error code and shut off. The code showed up and POST hit the kill switch almost simultaneously. It took an hour of restarting my computer righting down three of four digest and starting the computer again to get the entire code. After Googleing the error code I found a website that vaguely pointed to bad capacitors. After a closer inspection of my motherboard I confirmed that the caps where bulging. Scavenging through my junk box I discovered that I had every kind of capacitor possibly imagined except the 2500 pf  caps to replace the bad ones on the motherboard. I also have heard all kinds of stories about needing all kinds of specialized junk to work on motherboards like temp controlled soldering irons. all i had was the 20 year old 30 watt trash shack tinder box I annexed from my dads electrical box the year before. I wasn't letting any details like them stop me. So i rummaged through my box of junk some more and found another motherboard with 6000 pf caps. If I placed two of them in series i would end up with 3000 pf caps. Close to the 2500 pf i was looking for. There was also a 15 % tolerance to work in so i did some more math.
2500 + 15% = 2875
 (6000/2) - 15% = 2550 (Now that i think of it this should have bean 30% tolerance as the two tolerances would add together.)
After I finished the math I mumbled something about how close enough was good enough and decided to go on with the project.
I decided to take the caps of the donor bored first. I think thy must have used some kind of conductive glue instead of solder because it wasn't melting. I spent what seamed like hours bent over to board trying to get the solder to melt but it just sat there laughing in my face. I cracked after that hour and went for the heavy machinery; my rotary tool with a cut off wheel. I'm almost positive I was laughing maniacally as i slowly lowered the wheel to the board intent on cutting out the offending parts. It was probably because of this laughter that I inhaled all the dust from the Dremel in one big gulp causing me to have a coughing fit. Old motherboard 3 me zip (the third offence of the motherboard is a deferent story). I was about to through that cursed motherboard away in disgust at being thwarted once more by a peace of fiberglass. When the realization hit me that I could cut it too peaces with a pair of tin snips. Finally I would have my revenge on that board. It also got the capacitors off it to so it was win win i suppose. I ended up leaving the board on the bottom of the caps and just soldering wires onto the tag end of the lead that was still sticking out. Linking pairs of them together in series first.* Then I soldered leads onto the remaining tag ends to install into the board. Next I had to desolder the caps from the board I was working on. I was apprehensive at first because of my past experience with this posses but as I placed my iron on the first lead the solder melted almost before the iron hit it. all I had to do was push in the leads with the iron and the bad caps fell out. This was a huge relief i thought i was going to have to pull all the capacitors off the board by hand and solder to the exposed leads left behind.
 So I reassembled the computer and installed terned it on. It booted up on the first try. I later discovered that the on board Ethernet cart and sound card didn't work. So i added expansion cards for them. The computer worked for me for about a year before I no longer needed it and took it apart for other projects.

I do not recommend that you try repairing motherboards yourself it's a pain. This is simply to show how I solved a problem not to show you how you can do the same thing. I also don't recommend playing with electrolytic capacitors without knowing what your doing I've seen them blow up and it can be scary. I also never would have done this if I didn't have another computer to use as I might have killed the computer and all its parts.

*(Electrolytic  capacitors are linear so you have to use the right orientation or they will blow up.)

1 comment:

  1. These capacitors are soldered to big power planes, you need a big soldering iron to supply enough heat, minimum 60-80 W