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Testing transistors

I've posted this link several times, mainly because it shows dmm display pics. (I also have the Peak dca55, too.)
 
Just wanted to say this is the best how-to for checking transistors that I have seen to date-at least for me. I am still trying to figure out how to transistors work- I haven't got the whole "electron-hole" thing down in my brain just yet but this certainly helps this amateur troubleshoot in the interim. :thumbsup:
 
avionic said:
If your going to be testing a lot of transistors. Which I do. I love my little DCA.
file.php
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I need to buy one of these Peak Atlas meters... There are a couple of them really good, but probably need more advise for most common use...

Question: how do Darlington transistors measure on DMM? Not in the usual 0.45V to 0.65V, I guess?
 
Everything should be similar except the B-E junction. The B-E junction should be approximately double what you would expect in a similar bipolar junction transistor because there are now two transistors in series. The number isn't perfect as they can have different characteristics, along with the possible built-in resistor will throw off results.

I tested one of my spare parts darlingtons and got 1.1 volts on the B-E junction.
 
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avionic said:
Testing BJT transistors for shorts or opens.

The majority of "Bad" transistors are due to shorted junctions. This is my attempt to simplify the routine for those that may not already know the process.
Photo 1
Transistor lead identification - If this is unknown you will need to find a spec sheet on the transistor under test.Sometimes it is provided on the schematics " legend" or even silkscreened on the printed circuit board.
Photos 2 & 3
Testing the Base-Collector Junction***With your DMM in the Diode Check function -Attach test leads as shown.One direction should show -OL(open) - and in the other direction a similiar value to the one depicted in the photo ,depending on whether its a PNP or NPN determines the direction of conduction.
Photos 4 & 5
Testing the Emitter-Collector Junction*** As seen in photo. Both directions should show (open) in a good transistor reguardless of NPN or PNP.
Photos 6 & 7
Testing the Emitter-Base Junction*** Again depending on NPN or PNP. One direction will show (open) and the other direction a similiar value to the example depicted in the photo.

NOTE:The transistor in the photo is a " serviceable " example. ONsemi MJL4302A PNP

If your meter at any time - beeps continuously - and/or reads a low value close to zero . First verify your test leads are not touching.If they are not touching ---You have identified a faulty junction and a unserviceable transistor.

Good luck..I hope this is helpful..

Dave
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I know you like being challenged...:)

How do you do this with the transistor being "in circuit"?

Best

Soundork
 
audiodummy said:
Everything should be similar except the B-E junction. The B-E junction should be approximately double what you would expect in a similar bipolar junction transistor because there are now two transistors in series. The number isn't perfect as they can have different characteristics, along with the possible built-in resistor will throw off results.

I tested one of my spare parts darlingtons and got 1.1 volts on the B-E junction.
Click to expand...
I tested the two 2SD1953's - off circuit - I have here and got these values (red probe on Q lead):

B-C = .609
B-E = .725
E-C = .551
 
That's what I was expecting! Maybe found the problem in an amp! :)

Now I need only to find a substitute for the 2SD1953. I have a BD683 (also a Darlington), need to check pinout.
 
Hmm. The diode in the circuit may be skewing our diagnosis. Its a darlington with a diode across the emitter and collector.
 
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