A circuit board can contain hundreds, or even thousands of connections. When even one of those connections goes bad, the entire circuit board will stop working. Unfortunately, the only way to test a circuit board is to test the individual connections. You can narrow things down by looking for a bad connection, but you still may have to spend hours testing the circuit board to find the problem.
Instructions
1 Look at the board for cold solders or broken connections. Look for joints where the solder looks black or corroded, or look for cracks in the solder joints.
2 Mark every suspected bad connection with a small piece of fluorescent tape. If you have several suspect joints next to each other, use several pieces of tape to make sure you mark each one. You could use any sort of tape, but the fluorescent color will help you be sure to check every connection since it is so eye-catching. Use the same color of fluorescent tape for every suspect connection.
3 Turn your multimeter to the ohmmeter setting, and switch it on. If it has multiple settings, turn it to the lowest resistance. You will notice that, when the test probes are not touching, the resistance reads as infinity or whatever the highest resistance on your ohmmeter is. Touch the test probes together. The meter should read a resistance of zero or just slightly above. If it doesn't, replace the battery in your multimeter.
4 Touch one test lead to the component pin at the suspect solder joint, and the other to the socket. If the solder has made a good connection between the component and its socket, the resistance should read zero, and you can move on. If the resistance stays at infinity, you have a bad connection.
5 Remove the piece of fluorescent tape. If the connection was bad, use a different color tape to indicate that you need to resolder that connection. Continue checking the rest of the connections, then come back and fix the ones that need to be resoldered.
