in this instructable we'll replace failed capacitor in PC mainboard

the mainboard here is from friend's computer. it crashed randomly for few months and now it does not allways complete startup

this may - and in this board is - caused by failed capacitor. capacitors stabilize the power to components in the computer. when they go bad the computer gets spikes or 'flickering' voltage that makes it malfunction and damages it

Step 1: Tools

new low ESR (low internal resistance) cap

pin from message board

sharp soldering tool 30 W (more may be better but dont overkill) and soldering stuff

Step 2: Find It

most bad caps have visible damage. the last image shows ok (green) and failed (red) capacitors

Step 3: Find Replacement Cap

you need a cap that is

the same voltage (higher voltage will work but not as good)

the same (best) or larger (max 1.5 X) capacity

external size (not too large to stuck in other components)

low ESR (low internal resistance) - this means its fast enough to react to thin and sharp spikes of too high or too low voltage. most caps in computer mainboards are low ESR. most caps in other places are not.

there is a way to replace low ESR cap with standard electrolytic and ceramic connected in parallel. i think this hack is NOT suitable for computer

in the example we'll replace 6.3 V 1000 uF with 6.3 V 1200 uF from another dead mainboard

(the other board died with smoke after being installed without spacers between it and the wall)

Step 4: Remove Battery

before you start any work with the board remove the battery

Step 5: Remove It

see what side is the - side of the cap. you'll need it later

hold the cap and heat one of the points its soldered to. if the tool takes the point then tilt the capacitor to the correct side to pull out the entry

wait for the point to cool and do that with the other one

do so few times untill you get the capacitor out

if the tool does not take the point add a tiny amount of new solder to it

if the point is connected to a large area conductor in the board (it may be between the layers of the board too) it'll sink most of the heat. its ok just keep on heating it

dont heat the point if you feel the heat spread from it to the rest of the board or if you think you can damage something

Step 6: Clean the Holes

you took the cap out. now you need to stick in the new one and the holes are full of solder

if there is hole use the pin to make it larger so you can insert the capacitor. spin and tilt it in the hole from 2 sides of the board. dont press hard to not damage the conductive layer on the walls of the hole

if the hole is blocked try to kinda solder the pin into the hole. when it cools down remove it (its made of some metals that dont stick to solder)

Step 7: Insert the New Cap

insert the new cap with the - in the same side as the previous one

Step 8: Solder It

heat the point with the tool and give it a tiny amount of solder. heat it for about 2 sec more so the solder fills the hole

try to make the drop on the outside as small as possible

Step 9: Clean

when soldering some transparent material comes from the solder and remains on the board. sometimes its little conductive. if there are any conductive points nearby and it kinda connects them to the capacitor then try to break the path with a plastic card

do not damage the transparent paint that covers the board

if its just on the paint its ok - the paint is not conductive

if its only between the 2 points of the cap or the points are anyway on the same conductor in the board then its ok to leave as is

Step 10: Yay

Step 11: Test

install everything in the board and let the computer run. try to do what you could not with the bad cap

touch the cap to see if it heats. cool or little warm cap is ok. more is not ok (did you install it in the correct direction ? is it compatible with the cap you replaced ? are there any other failed components in the board ?)