Hi, I came across this on the internet for transistor testing.
"Connect the negative probe of the multimeter to the base output (usually it is a black probe), and the positive (red) first to the collector and then to the emitter. Obtaining a value in the range of~500 -1500 Ohm confirms correct operation of the transistor."
I tested 2 npn transistors and both gave infinite readings. They were both in the same circuit so I suppose they both could have failed.
Can anybody confirm that this test is correct?

 

Hi,
test transistors in diode mode on your meter. 0.4-0.8 V is OK.
Transistor is not a resistor with a defined resistance

 

Hi,
test transistors in diode mode on your meter. 0.4-0.8 V is OK.
Transistor is not a resistor with a defined resistance

@Pyrex is right - you must use the diode test function.
Also, to test an NPN transistor, base should be positive (red probe) and test between base and emitter, and between base and collector, with base positive in both cases.
For a PNP transistor, base should be negative.
A further test you need to do is to check for continuity between collector and emitter - if there is any, it fails.

You can test JFETs in a similar fashion - gate to drain and gate to source on diode test, but JFETs do have continuity between drain and source.

 

Furthermore, the polarity of your test leads depends on the test meter. Is it an analog meter or digital meter?

You need to do 6 tests.

b - c
b - e
c - e
c - b
e - b
e - c

 

And that test, even if done correctly, tells you the transistor is bad if it fails, but does not mean it is good if it passes. It could still be bad in other ways (for instance, very low or no gain.)

 

I got a similar circuit to this one as a code practice oscillator from the ARRL Handbook.
My circuit used two 1.5V batteries and was also used as a battery check.
I used two transistor sockets and thus used this to quickly check PNP and NPN transistors.

 

Yes, that would be a functional test.

I just use my $20 component tester, which will identify the transistor type, pinout and the gain.

 

I am with BobTPH; I also own a low cost transistor tester that has proved invaluable over the 12 years I owned it.
But to your question, you would have to perform the 6 tests as MrChips outlined.

 

While we are on the subject of transistor testers, I also recommend -for more advanced users- obtaining some sort of SMT adapter, at least for the small yet very common package, the SOT23

 

They were both in the same circuit so I suppose they both could have failed.

Are you testing the transistors in-circuit?

A junction test will only give a DORA (Dead OR Alive) indication. A curve tracer is a better tool for characterizing transistors.

When I was a technician, I used a continuity checker as a quick way to identify dead transistors in-circuit. Diodes in parallel with junctions can give misleading results...

 

Now, if you want to get really sophisticated, you can build this simple I-V curve tracer.



https://forum.allaboutcircuits.com/threads/diy-i-v-curve-tracer.184368/