hFE on DMM

Sure you know which legs are what ?

....... Phil

I'd agree that you've probably got the E, B and C leads turned around. It does make a difference. You should see a number greater than one -- possibly 20 to 200.

Go look at the data sheet. The quickest way to do that would be to go to the NTE site and punch in the manufacturer part number:

It will then show the NTE equivalent repair part. Click on the data sheets link to see the part pinout, and insert the leads into the DMM accordingly.

Good luck Chris

What do you mean by "correctly" ?

Graham

ha, i have a cheap meter that can turn the leads in the circuit to find the highest Hfe. i don't have to make sure the leads are in the correct hole! :)

I mean that I have correctly identified the pins. It is a 2N2222A transistor. I looked up the datasheet and found the correct information, but I still get the solitary "1" on the screen.

--- If you've connected the transistor to your DMM correctly and you can't tell whether the transistor is good or bad, then you either have a bad meter or a bad transistor.

In order to find out where the fault lies, (assuming your DMM has a diode test function), do this:

Set your meter for diode test and connect it across the base to emitter junction of the transistor. If it reads "OL", reverse the connection of the leads. If, after that, it still reads "OL", then the base to emitter junction has burned open and you have a bad transistor. If it doesn't, and it reads something like "0.7", then the base to emitter junction is OK.

However, if it reads close to zero, then the base to emitter junction has been burned shut and you have a bad transistor.

If those tests are successful, then without disturbing the lead connected to the base of the transistor, disconnect the lead connected to the emitter and connect it to the collector. The reading should still be around 0.7V.

If it isn't, and it's close to zero, then the collector to base junction has been burned shut.

If it isn't and your meter reads "OL", then the collector to base junction has been burned open.

If both of those preliminary tests were successful then, for a final test, set your DMM to an "OHMS" range where 10k ohms can be easily detected and connect the lead with a positive output to the collector of the transistor and the other lead to the emitter of the transistor. Your meter should read "OL".

If it doesn't, you've got a bad transistor.

If it does, then lick your fingers and pinch the collector lead between the thumb and forefinger of one hand and pinch the base lead between the thumb and forefinger of the other hand. If you do that and you can change the resistance indicated by the meter by squeezing and relaxing the pressure exerted on the base lead, you've got a good transistor.

-- JF