MOSFET Testing using a Multimeter

This short article will deal with testing power MOSFETs using an ordinary digital multimeter. Anybody who have ever tried this must have marvelled at strange readings and short circuits found even on surely working devices. Of course, there is no magic involved!Testing bipolar transistors, whether low or high power, is all plain sailing if you have just an ordinary ohmmeter available and know (1) the connections on the device and (2) the six steps involved. Such a simple test should spot 8 out of 10 defective bipolar transistors, although your editor had to admit defeat with some high-power UHF RF transistors he tried to examine the other day. For example, an MRF646 50-watts ‘beast’ checked out just fine electrically but its in-circuit power gain was nothing to write home about! Returning to the subject of our article, MOSFET testing is a different (but not necessarily nasty smelling) kettle of fish.