Resistors are quite easy to test. Of course one should start with the visual test--if the resistor is blackened or burned then it's best to throw it away. Next, determine the value the resistor should have by reading its color code. Set your multimeter to the appropriate resistance range, and measure. If the resistance is within the marked tolerance, the resistor is good, and you can use it in your projects. Otherwise, throw the resistor out; even if it still conducts, a marked difference in resistance from its rating means it's failed, and its resistance may not remain constant.
Again, start with the visual test. If it's burned or blackened, throw it out. Additionally, electrolytic capacitors can leak--if there's a fluid pooled around a capacitor, clip off that entire part of the PCB; the electrolyte is slightly toxic and corrosive to skin. If an electrolytic capacitor appears to be bulging, even slightly, desolder it carefully and dispose of it immediately; it's about to leak or explode. Otherwise, it's time to move on to the multimeter.
Probe the resistance of the capacitor. If it's an electrolytic or other polarized capacitor, ensure you connect it the proper way around--the side with the stripe should be probed with the ground(negative) probe of the multimeter. If the polarization is not clearly marked, then it's nonpolarized and can be used either way around. You should read a large resistance, though it may take some time to reach a steady value as the capacitor fills up. If you read a constant near-zero resistance, then your capacitor is useless. Otherwise, it's good. If your multimeter includes a capacitance meter, use that to check that it still has its nominal capacitance.
Inductors are difficult to break; there's usually no need to test them. Should you want to anyway, a guide to testing them will be added here soon.
Transistors are difficult to test and easy to break, so be careful testing them. This guide will assume a TO-92 package on your transistor. First, read the part number on it. The following table lists the properties of several common transistors. Pin 1 is the pin on the far left when the transistor is viewed facing the flat side with the pins pointing downward.
|Transistor part number||Pin 1||Pin 2||Pin 3||Type|