Before repairing a circuit board one must diagnose the problem and identify the failing parts. In most cases a component-level repair is required, that is, one or more components must be replaced with new ones to make the circuit work again. Most circuits are composed of passive and active components. Passive components are the ones that do not require a power source to work, for example, resistors and capacitors. A failing passive component can be identified easily but a bad chip is much harder to diagnose.
Turn the soldering iron on and set it to about 450 Celcius.
Use desoldering braid and soldering iron to remove solder at the pins of the component that needs replacement while gently pulling the component out using tweezers. Do not pull hard as it may damage the traces on the board. The best way to desolder is to place the braid on top of the soldered pin and gently push it with the soldering iron tip while pulling the component using tweezers. Do not use desoldering braid for passive SMD components, rather gently touch the two terminal sides alternatively in succession with the soldering iron tip while pulling the component with tweezers. This will melt the solder on two terminals, and the component will come out without use of any force.
Remove all of the remaining solder at the pads using desoldering braid and the soldering iron tip. Note that the solder on the pads connected to ground will take longer to melt.
Use alcohol swabs to clean up the pads and the space around them.
Place the new component on the board and align its pins so that they are approximately in the middle of the pads. If it is a through-hole component, push the leads through the holes on the board. Do not cut the leads yet.
Solder the component pins one by one using solder and the soldering iron tip. For this, place the soldering wire on the pin and touch it with the tip of the soldering iron. Pull away the tip as soon as the solder melts. Do not use excessive solder as it may flow to nearby pads or ground plane and create shorts in the circuit. If the component is a through hole type, the leads will have to be soldered on the other side of the board. Turn the board over and place it on a flat surface. Solder the pins to respective pads using soldering wire and the soldering iron tip. Cut off the excess of the leads using a cutter.