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Bipolar Junction Transistor Testing Basics

Thanks EW
The TO-3's in a KLH model 52a I'm working on are A'ok.
Hoping a recap is all it needs.
Nice to learn something practical today.
martin

:thmbsp::thmbsp::thmbsp:Yes...this should be a sticky:thmbsp::thmbsp::thmbsp:
 
2sc3860 testing

Will a standard diode test work for this transistor?

I am getting "OL" on all six connection combinations. Is this because the transistor is bad or because my diode tester is unable to work through the 10k resistance?

My first time to encounter this type of transistor. For those, like myself, not familiar with this it has a 10k resistor in series with the base. The datasheet refers to this as "on chip bias resistance".
 
Good question. Try a known good transistor and after confirming that you can verify its status, add a 10K resistor to the base and see how it tests.
 
Good answer, thanks. Should have thought of that myself :bash:

Will report back later tonight.
 
OverLoad was right. Apparently my diode tester will not work with 10k ohms in series with the base as it is in the 2sc3860.

I have some extra 3.3k resistors so I twisted three of them together in series and the end of one of them to the base of a ksc1845. This rig gave me 4 convenient test points - 0 ohms, 3.3k, 6.6k, 9,9k.

With no resistance in series with the base of the ksc1845 my tester showed .68v B-C. With 3.3k in series the tester worked but the B-C voltage was 1.96v. No go with either 6.6k or 9.9k in series with the base, got the "OL" reading just like on the 2sc3860.
 

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EchoWars ...I did some further testing on that 2sc3860 and would be interested to hear your thoughts.

Since my battery operated DMM based diode checker was unable to give any results, I thought why not try a different instrument, i.e. my BK 878 LCR meter. Maybe the LCR meter outputs a stronger test signal than the DMM? In any case I did get some results testing resistance on the 1M ohm scale of the LRC meter:

R B kOhm
B C 580
B E 615
C E 55

B R kOhm
B C 200
B E 620
C E 65

R and B in the heading indicates the meter lead. I was surprised to get readings in both directions. The kOhms numbers are approximate, the readings would not settle in on an exact number, and the alligator clips on my leads are kind of sloppy so taking the readings was not easy. But I did double check most of them.

Would it be correct to imply from these readings that the on-chip base resistor of the 2sc3860, as well as all three of the transistor sections, are at least functional, i.e. neither open nor shorted? Or is that crazy talk?
 
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Thank you EW for for all the effort put into this topic.
There is a book that I purchased from Radio Shack when I was maybe 18 that some may find useful. The title; "Getting Started In Electronics" by Forrest M. Mims. First published in 1983 then 2000. The book is in paperback/magazine format, black and white and gives a good basic education of how all the different electronic components work and influence the world that they live in. Plus it teaches the reader to read a simple schematic along the way. At the end of the book there is a section of 100 simple electronic projects that you can DIY, all via schematic.

tom
 
Can someone please tell me if I need to remove the component from the PCB in order to do the tests? I've been asking on other threads but not getting a clear answer. My problem right now is quite a few of my readings check out except.

For NPN D880, I'm getting a 1.2V from Collector to Base instead of reverse bias
For NPN D880, I'm getting a 0.6V from Collector to Emitter instead of reverse bias

For PNP B834, I'm getting a 1.2V from Base to Collector instead of reverse bias
For PNP B834, I'm getting a 0.6V from Emitter to Collector instead of reverse bias

Thanks.
 
Yes, definitely need to remove from the PCB for this test to work properly, otherwise the rest of the circuit distorts the result.
 
Testing transistors

Thanks guys. Response much appreciated. I saw some "Kits" on the web that claimed to be able to test transistors in circuit, but I'm going to drop that idea.
 
A diode test is not a definitive test...only an indicator that the transistor has a 'better than average chance' of being fully functional. I'd say the diode test is good to catch about 65% of failures.
 
kenwood61 said:
Thanks for the thread Glenn!

I have a question about measuring diodes in series. Specifically, 1N4148 in series to replace VD1212 diodes. When I measure a single 1N4148, no problem. But when in series, I can only get a measurement on the leads for each single diode. When I try to measure across both, I get "OL". Since the measurement for each diode is good, I know something else is up. Can you explain?

Thanks!
Click to expand...

its because your meter hasn't got the voltage / power to do it ..you can make a simple circuit with a 9v battery and the correct value resistor to limit the current then measure voltage drop over the diodes .
 
kenwood61 said:
Thanks. Short of doing that to be 100% sure, is it a safe assumption that if the mechanical/solder connection is solid, and each diode is measuring correctly . . . that the diodes in series are good to install?
Click to expand...

yes as long as they are actually wired properly .
 
yes that's the idea ...i suppose you wouldn't be far off by measuring voltage drops for each then adding results together .
 
this is a Classic Tek Type 575, for testing and matching pairs.

575-1.jpg


The old instrument can load the test transistor up to 400 Volts, up to 200W power. It will draw the complete curves family on the screen, well calibrated.
All currents are well limited, but a wrong setup can burn the transistor in seconds, so the study of his manual is strongest required before using it for a test. There are 2 sockets to compare A with B simply by using the switch between

575 is sometimes to find in the bay and on ham markets. It requires a lot of space, it is warm and heavy, but still a greatful helper in match and selecting transistors.

It have a brother, Type 570, this do the same with tubes. :-)

greetings
Martin
 
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