View Full Version : Diy Transistor test circuit

06-16-2013, 06:02 PM
Before soldering all your parts ( like I did with the ren 48lsd ) it is probably a good idea to verify their type and that the are actually working .

de-soldering is no fun when building a new board , future repairs are less a burden .

but on a new board you want to take steps to assure it will work correctly without having overlooked something.

This is one of those somethings . :)

Hope this helps for first time builders .



06-17-2013, 04:29 PM
My Mastercraft Multimeter (52-0052-2) has that functionality. I haven't tried it yet since it was not much of an issue for me. But it is handy in case one needed to know. However, if the test failed then it could be that the E B C selection was incorrect - so a datasheet may still be needed.

Wayne J
06-17-2013, 04:41 PM
My DVM has that function also and I have never used it. I am going to try it out when I get home now, just for kicks.

06-17-2013, 05:45 PM
That makes a neat way to test a transistor. Takes some time and a little effort to make the transistor tester, but there is a simpler, easier way if your DVM/Ohmmeter doesn't have a transistor tester built in.

Turn the DVM/Ohmmeter to it's lowest OHMS range. Put the positive lead (red) on the base (usually the middle lead) and the negative lead (black) on one of the other transistor leads. If the DVM shows a low ohms reading, this is a NPN transistor. Conversely, put the Negative lead on the base and the red lead to one of the other leads. If the meter reads low ohms, this is a PNP.

Positive voltage on the base of a NPN transistor turns it on, both to the collector and emitter. Negative voltage on a PNP turns it on, both to the collector and emitter.

The tester makes an easier way to determine the sex of a lot of transistors, but if you have just a few, the DVM/Ohmmeter works just as easy and quicker.

This test method will also determine the ANODE of a diode, if it isn't marked. Put the leads on the diode. If the meter shows a low ohms reading, the RED lead is on the ANODE. The black lead is on the CATHODE, which is the bar on the diode symbol.

A transistor is just two diodes connected together. For NPN, the diodes are the ANODES connected, forming the Base. PNP is two diodes with the CATHODES connected together.