Transistor diode test question?

I bought 2 sets of Sanken output transistors to use as spares for a Sansui AU-D907FE when I tested them with a DMM diode tester (Fluke 87 V) both of the 2SA1216 tested Ok! But one of the (2SC2922) read 0.570v from Base to Collector and 0.570v from Base to Emitter? The other ''Good'' one (2SC2922) reads 0.547v Base to Collector and 0.550v Base to Emitter as it should. I noticed that Base to Collector on the former would flicker from 0.570 to 0.569v every now and then? I've come across this same thing before when testing transistors in circuit but they still worked perfectly. This one is tested out of circuit so is this transistor going to be Ok? I've ordered another transistor just to be cautious but I would love to know what the score really is? :D


Paid Member
2003-06-12 7:04 pm
Maine USA
A transistor is two diodes. They are similar but not identical. Two transistors may mis-match 20mV (0.570 vs 0.550). 1mV wobbles are normal.

I do not see a problem here. Zero or infinity would be bad.

> this transistor going to be Ok?

A transistor can be a fine low-voltage diode but break-down blocking high voltage. Can't tell from the tests you have done.
A transistor can be a fine low-voltage diode but break-down blocking high voltage. Can't tell from the tests you have done.[/QUOTE]

You do know how to test a transistor with a diode test? On a good transistor, the Collector is always a lower voltage then the Emitter to Base so if they are equal there must be something wrong I would think?
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I should have made it perfectly clear that I used the diode function on the DMM to do the transistor test so if anyone has ever done this they would know that Base to Collector always reads a lower voltage than Base to Emitter does? So if they both read the same then that would be cause for concern I would think? because the Emitter current is always equal to the sum of the Base current and the Collector current, I would like to get some advice from someone like an Electrical Engineer who actually knows if my transistor is within or without its specs with that tiny intermittent voltage on the Collector?
Be aware the meter diode test function is just a very crude test. It does not put real world currents through the part, nor does it subject the part to real world voltages. You can verify with a diode that the voltage across its junction changes with current.

Your meter cannot guarantee performance to spec. What it is good for is finding BAAD parts. Like grossly defective. Your meter is trying to display 0.5695v on one less digit, so sometimes it will appear as 0.569 and sometimes like 0.570. This it the meter, not the part.


2012-02-10 12:12 pm
I understand your concern. There is obviously something odd with that transistor of yours, measuring the same voltage drop on B-C and B-E. You trust your expensive fluke meter and that is ok. If I were you, I'd test it for hfe and compare to manufacturer datasheet, assuming transistor is not faulty.
This is hopeless! I assumed that any replies would be from people who know how a transistor works? This thread is now closed. I will ask a transistor manufacturer about this technical aspect.
You have been answered by Electronic Engineers and VERY experienced Techs (think over 60 years experience :eek: ) yet you find them wrong because thay don´t follow your deeply flawed "theory" about transistors work?
Or your absolute lack of understanding on how digital displays work?

You are WASTING your time here, go grab your bicycle and RUSH to the airport to take the next plane to Sweden, a Nobel Prize is waiting for you.