Before repairing an electronic device, you first need to find the faulty component on its printed circuit board, or PCB. this can be a challenging task, as different components require different test procedures. It makes sense to check transistors first, as you can do a quick in-line test. Passive components such as resistors and inductors fail less frequently, although they too can be damaged or burned out.
Instructions for use
1 Before checking the board, turn off any power to the circuit. Disconnect the power cord from the AC outlet.
2 Check the circuit board for fuses. If you find one, use long-nose pliers to pull it out and see if it appears to be blown. If you have a glass fuse, look at the filament inside. A blown fuse will have a broken filament. If you have a ceramic fuse, check it with a multimeter. Set the multimeter function to continuity and touch the probe of the multimeter to the metal end of the fuse. If the meter beeps, the fuse has continuity and is good.
3 Check the components on the board for signs of physical damage. You may see burn marks, cracks, broken wires, bumps, or crushed components. Assume that any component that appears damaged is faulty.
4 Turn on the digital multimeter and set it to the diode test function.
5 Identify the bipolar (NPN or PNP) transistors on the schematic and locate them on the board. Touch the multimeter probe to the collector and emitter pins of each transistor. The meter should read "open circuit" or "high resistance".
6 Touch the negative probe to the collector of each NPN transistor and the positive probe to its base. You should get a reading of a few hundred millivolts. Move the negative probe to the emitter. You should get a similar reading. Reverse the probe. The meter should now read "infinity", "overload" or "high" resistance. Move the positive probe to the collector. You should get a similar reading.
7 Connect the positive probe to the collector of each PNP transistor and the negative probe to its base. The meter should read a few hundred millivolts. Move the positive probe to the emitter. You should get a similar reading. Reverse the probe. The electrical meter should now read "high" resistance. Move the negative probe to the collector. You should get a similar reading.
8 Replace the individual integrated circuit (IC) with the exact same type of spare part, if the IC is a socket. Test the circuit by plugging the power cord back in and turning the device on. If it previously performed poorly or was completely dead, it is now working properly, indicating a problem with the IC.
