Hi
Well, let's see ... transistors have three leads. To test one anywhere near properly, you need to bias (say) the collector relative to the (say) emitter and inject a measured current into the base. You then measure the collector current relative to the base drive to get Hfe.
Cheap / simple approach:
Short the collector to the base, see if it looks like a diode.
Needless to say, the first approach is a bit complex to implement. The second one is drop dead easy. The problem is that the second one only tells you that in some way the transistor looks like a diode. There can still be a lot wrong and you have a diode in there somewhere ....
Bob
The way I do a "go-nogo" test is thus:-
For an unknown transistor,first check which lead is the
base,by noting the diode junctions.
The
base will have junctions with both of the other two elements.
Whether they are NP or PN will identify the device as PNP or NPN.
Assuming an NPN for now,place the +ve DMM lead on one of the
non-base leads & the -ve on the other.
Now "spit" on your finger & place it between the +ve connection & the
base.
You will see a reading on the DMM (in diode test mode),because the transistor is partially turned on.
Note this reading.
Reverse the DMM leads,
Repeat the test,& again there will be a reading.
The highest current (lowest resistance) reading shows which lead is the
collector,which is the
emitter,& whether the thing works.