Replacing Electrolytic Capacitors

I have had to replace electrolytic capacitors on 3 DELL GX520 now. That's a pretty high rate of failure since the company only has 7. 3 have had power supplies replaced under warranty and one has had a hard drive replaced under warranty. The company had recently purchased additional extended warranties after the original warranty had expired and dell would not replace the units. They claimed that it had to be due to a power surge and power surges are not covered under warranty even if they are on a quality UPS. Here is a step by step on how to do it. While this is a about the GX520, the same principle can be applied to any electronics that have electrolytic capacitors. I hope someone can find this useful.

1 - Open case and clean out the dust bunnies. There is the typical dell style Japanese puzzle box type way to open the case. When you pull on it, the top cover will pop up. When you clean it, it helps to have an attachment with the bristles in order to scrub the built up dust out of the grilles. Remember that electronic integrated circuits are very sensitive to static electricity and that most household vacuums generate a lot of static due to rushing air over plastic. It helps to use a can of "Dust Off" or any similar compressed air designed to blow off electronics. Don't let yourself or any curious children breathe in the air directly. While I have heard that it can get you quite a buzz, it can also cause severe brain damage or even kill you. You can also get ESD safe vacuums. I have been meaning to get one but since I have not, I just take my chances with the Dyson.

2 - Remove the hard drive, unplugging the SATA and power cable. It is easiest to unplug the SATA cable from the motherboard since it is attached to the bottom of the carriage with a little clip. The power cable has a little cable tie on the side of the drive carriage that is simple enough to undo. Then squeeze the blue things together and lift. It kinda hinges in the back on the case.

3 - Remove the CD-ROM drive, unplugging the special, mobile ide+power ribbon cable from the motherboard. You'll have to lift the lever marked with blue and then slide the drive toward the back of the case and then lift it out.

4 - Remove the floppy drive, unplugging the special, floppy+power ribbon cable. Just like the CD-ROM drive, lift the lever marked with blue and slide it back and then up. The ribbon cable wraps around the fan shroud and is easy enough to untangle.

5 - Remove the CPU heatsink by unscrewing the 2 front screws that retain the heatsink toward the front of the case, behind the fan. Once the screws are out, the whole assembly hinges back toward the back of the case. Tip it up and pull it out.

6 - Remove the screws from the heatsink hinge piece and remove it from the motherboard.

7 - Remove remaining 4 motherboard screws. There is basically one in each corner of the motherboard.

8 - Unplug remaining cables. The power connector, just like any standard ATX power supply, you have to pinch the clasp while pulling to release. The 4 pin P4 power connector that is right underneath where the floppy drive was; push the clasp just like the power cable. Finally, there is the ribbon cable that attaches the front assembly with the USB, power switch and LED's, just pull it up and off.

9 - Remove the motherboard from the chassis. It can be hard with the ribbon cable for the front LEDs and USB ports and with the little ribbon cable at the front by the fan but you can get it if you push them out of the way. Once you get the motherboard out, it is a good idea to take out the front fan. Just squeeze the clip in the corner and hinge it out. Now you can clean the fan and the front grille thoroughly.

10 - Identify the capacitors that need to be replaced. you can tell that they are bad because the tops are not nice and level anymore. Sometimes you can even see corrosion or residue like I have on one of mine. Electrolytic capacitors are filled with a fluid for the dielectric. I guess they either overheat or the fluid expands when it gets too much of a jolt. Whatever happens, it makes them bubble up and once they bubble up, they don't work the same as they used to. They don't need to be bubbled up much to be bad. Just compare them to all of the others to find the ones that aren't quite flat. They can't all be bad.... right? Most of the time, capacitors are used to clean noise off of the power lines. Often, when they go bad, it will not cause a complete failure, but your computer may crash more or perform slowly.

11 - Remove the capacitors. I use a $10 soldering iron that I got at Wal-Mart. There are definitely better ones out there and if you intend to do work on fine chip components, the cheap one will not due. I place the iron on one lead of the capacitor on the bottom side of the board. Then lift that lead through the board by bending over the capacitor. Usually, there is not enough play in the leads to allow it to pull all of the way through. You will need to do the other lead and kind of teeter totter it back and forth until you get both leads all of the way out.

12 - Remove the remaining solder from the 'via' using wick or solder sucker. The holes that go through the board are known as via. They are there to allow through hole components to go through the board. There are also smaller via that are masked over with the green layer that allow the circuits to connect the multiple layers of the printed circuit board or PCB. You will need to remove the old solder form the via so that you can easily insert the new capacitors. I prefer to use a solder sucker but you can also use solder wick. I will typically have to add some solder to the remaining solder since the old solder is too 'cold' to flow properly. New solder typically has a flux core. The flux is a chemical that causes the solder to melt more evenly. I think it eliminates the oxidants in the metal which allows the heat to disperse more evenly. Whatever it does, the solder goes all shiny and bubble up more instead of going flat and spiky. When it bubbles up better, the solder sucker can take it all in one good suck and you will not have to reapply heat over and over. Reapplying heat can eventually damage the board. It seems that frustration with cold solder is your worst enemy when it comes to soldering. Flux can be added separately but I can never find it anywhere but I can do fine with just the flux core found in the solder.

13 - Get the right replacement capacitors. Along the side of each capacitor it will say the ratings for it in µF (micro farads) and V (volts). I placed the order for my replacement capacitors with mouser.com. You just need to search for the capacitor with the ratings that match the capacitors you have removed. For my replacement, we have 2 2200µF/6.3V and 1 1800µF/6.3V. They were 51¢ ea. and 36¢ eac. respectively so I ordered 20 of each. I also ordered 30 1000µF/6.3V capacitors @ 14¢ ea. since they also seem to be a popular replacement. The shipping was cost $7.95, that's why I decided to order so many. It seems a waste to spend more on shipping than on the parts that are being shipped. Mouser did not have pictures of the capacitors, or if they did, I didn't pay attention and when I received the capacitors, they were quite differently shaped than the ones I was replacing. It didn't really matter since they still fit in between all of the other components without a problem.

14 - Insert the new caps. Pay attention to polarity. There is a stripe, down along the side of each capacitor. The stripe indicates the negative side. The negative lead (wires out the bottom of the capacitor) will also be shorter that the positive lead. On this motherboard, the positive side is indicated with a white triangle and a plus sign. Other motherboards may indicate polarity differently but generally will at least indicate the positive with a plus sign. If you cleaned out the via properly, the leads should slide through effortlessly.

15 - Solder new caps. You'll need to turn the motherboard upside down in order to solder it. But when you do, the cap will probably fall out if you are not holding it in place. But it is hard to solder with only one hand. So you will need to 'tack' it in place. Just grab a small glob of solder on the tip of your iron and apply it to one of the leads while holding the cap flush to the board. Since you will not be able to flow solder into the joint, it will be a very bad solder joint but it will allow you to let go of the capacitor and use both hands to solder the other lead. Now you can flow the solder into the joint with one hand while you apply heat with the other hand. Once you get the un-tacked lead soldered, you can return to the tacked lead and flow in solder for a clean joint.

16 - Inspect solder joint. You want the joint to be nice and shiny. There should also be a nice fillet, or curved slope from the surface of the motherboard to the length of the lead; You do not want a blob. There should also not be any contamination of other material, like residue from your soldering iron and there should be no pinholes in the solder. If your joint does not look good, you can reflow the solder with your iron, you can also flow more solder into the joint. The flux from the solder will allow the joint to fill and set properly. If you apply heat too long, all of the flux will burn away and you will be left with a cold solder joint, which is not shiny. If you need, you can also suck the solder away and try again. Be careful though, prolonged and repetitive application on the iron to the motherboard can cause damage that cannot be undone.

17 - Clip the Leads. You should use a pair of dikes (diagonal pliers) but since I seem to have lost mine so I used my lineman's scissors. I love those lineman's scissors. You used to have to special order them but now you can get them at Home Depot.

18 - Reassemble the Computer. It is a good idea to replace the thermal paste between the CPU (Central Processing Unit) and the heat sink. I had some 'Arctic Silver' paste lying around. I think I ordered it from Tiger Direct a while ago. If you are placing an order for other stuff it is a good idea to add it to the shopping cart. You should always have extra thermal paste around. I have heard that most of the Xbox360 red ring problems can be solved by simply replacing the thermal paste. I have not had to personally do it but I have heard that others have had success with it. A while back, when I used to over clock my computers, I would have to sand down the heat sink and CPU with high grit, wet dry sand paper and very lightly apply really good thermal paste. Remove the old paste with a paper towel. When applying to the top of the CPU, use 5 small globs of paste to ensure even dispersal as it is squeezed between the CPU and the heat sink. only apply to the CPU or heat sink; if you apply to both, you will have too much paste Once you have the motherboard and heat sink installed back in the case, reassemble the rest of the parts.

19 - Power up the computer. Most Dell computers of this generation have a self test initiated by the motherboard when power is applied. The power light will turn on momentarily and you will hear the fans spin and then it will turn off. If it does not, chances are you did not get it fixed. If you press the power button and no smoke comes billowing out of the computer, you are probably good to go.