Testing Transistors

[speakerman1]

I have a trans tester. Do I need power on to test them?

Larry

 

[rtp_burnsville]

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.

 

[jbeckva]

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.

 

[nakdoc]

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.

 

[laatsch55]

Need more current for Darlingtons???

 

[nakdoc]

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!

 

[laatsch55]

Yep Got a 179, glad I spent the extra $$$$$$$

 

[nakdoc]

Actually the #1 reason to buy a Fluke is they turn themselves off. #2 is you can drop them and they survive.

 

[laatsch55]

All features that get constant use here.

 

[oldphaser]

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

 

[Bradrock]

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