Testing Resistors

If you suspect a resistor, examine it visually first. Is it scorched or burned looking? Does it have obvious chips or cracks? Is it soldered firmly in place or does it feel a little loose when you wiggle it a little?

Resistors can fail in the following ways:

• Their resistance may drift from it's nominal value, sometimes dramatically. Measure the resistor with an multimeter set for ohms and see if it's within tolerance. These things make a resistor more likely to have drifted in value: high nominal value, heat stress (near a hot component or gets hot from the current it carries), high voltage across it (plate resistors).
• They may be completely open (ohmmeter test!)
• They may be mechanically damaged: cracked or chipped, or the leads may be loose on the body or the leads may be broken themselves or poorly soldered.