Testing Transistors

The testers I have used were not the in-circuit type and supplied power as needed. One just plugged the transistor into a socket and pressed a test button. With that said I am guessing that the circuit would be not powered. A transistor is sorta like two back to back diodes.
 
Yep, and to add - if "in circuit", there could be other components in parallel that will make the tranny look bad, so just be aware of that.
 
What kind do you have? Some work well in circuit, others do not. In almost all cases a diode check on a digital meter will test all but darlingtons.
 
Many digital meters will not forward bias a darlington, so it is a voltage limit, not current. Likewise those of Sansui and Marantz SVT3 and 4 diodes. Everyone thinks they are open, but their meters can't bias them on. The Flukes can measure up to 3 diode drops. Often you can check from pre-driver to output in one quick test!
 
There are many different means and methods to test transistors.

I use a variety of test equipment depending upon whether the transistor is a small, medium or high power device.

A basic Digital Multimeter alone will not tell you whether a transistor is truly "GOOD". Fundamentally, all a DMM can really do is tell you whether you have an open or a short.
A DMM will not tell you whether a transistor is genuine or counterfeit.
A DMM will not necessarily tell you whether the transistor is "leaking" unless of course it is "leaking" a lot.
DMM's with a hFE/Beta function may work ok for small transistors but in my opinion are not suitable at all for high power transistors.

With the input of others and an on-going evolutionary process....... at about the time one thinks they know it all...... along comes another test I now perform that I hadn't in the past.

As time permits, I will begin to discuss the tests I am now performing. I have already shared this information via phone with a few active members in the forum. I hope to one day have a Excel spreadsheet with all the data I will be collecting.

I will end for now, as I haven't had enough sleep.

Ed
 
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Thank you Ed. I want to know about Curve Tracers.
 
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