Transistor Test Equipment

You can use a multimeter for simple transistor tests.

Technicians use different types of electronic test equipment to check transistors. They use multimeters and leakage testers to see if the transistor works or not, and a gain meter and curve tracer to reveal the subtleties of its operation.

Multimeter

You can do a quick check on a transistor with a multimeter, treating the transistor as two back-to-back diodes. Each diode should have low resistance in the forward direction and high resistance in reverse. If you don’t see this, the diode may be shorted or blown. Many hand-held digital multimeters now also measure a transistor’s current gain, also called Hfe or beta.

Curve Tracer

A transistor curve tracer is a dedicated measurement device. It displays a set of graphical curves for the transistor being tested. If you know how to interpret the curves you can determine the transistor’s gain, breakdown voltage and impedance.

Leakage Tester

As with diodes, transistors conduct current in a forward direction and block it in the reverse direction. A leak detector looks for the small amount of current a transistor leaks in reverse. Using one, you can determine if the transistor is good or if it needs replacement.

References

• All About Circuits: Meter Check of a Transistor
• University of Pennsylvania: The Transistor Curve Tracer
• Integrated Publishing: Transistor Leakage
• Technician’s Toolbox: Hfe