Electronics > Beginners

Q: Identifying Transistor Terminals

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mikeselectricstuff:
The Peak is a handy box, especially when doing repairs. However if you don't have one, you can easily identify the pinouts of standard (working!) BJTs using the diode test function of a DMM and a wet finger :

1) Connect probes to pins at random til you see a voltage  around 0.6-0.7V
2) Swap the -ve lead to the unconnected pin. If you get 0.6-0.7V again, it's NPN and the +ve lead is base. If not, it's PNP and the lead you originally had the -ve connected to is base. Confirm this by returning the -ve lead to the original pin and swapping the +ve to the other pin - you should again see 0.6 to 0.7v. 
You now know if it's NPN or PNP, and which lead is base.
3) Connect the leads to the emitter and collector (i.e. the ones that are not the base identified above).
4) Lick your finger (you  want slightly damp, not dribbling with drool). If it's an NPN, apply wet finger between base and the + lead, if PNP, between base and -ve lead.
5) Swap leads and repeat step 4.
In the orientation that gave the lowest reading (<1V), or required the least finger pressure, the + lead is collector if NPN, Emitter if PNP.

williefleete:
go back to basics

this is plastic board and screws basic and similar to Dick smiths funway into electronics volume 1 "transistor tester"
attach a "reversing switch" and inverse parallel LEDs so you can test PNP's and test them reversed or make two of them

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