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Bipolar Junction Transistor Testing Basics

The TO-126 is most likely ECB (I can't think of a TO-126 that isn't ECB). However, never assume the pin-out just from the case style. There are of course exceptions where the pinout is always uniform such as high power transistors (ex. TO-3P will always be BCE) but why guess.

Here is a simple trick you can use to determine the pin-out of an unidentified but otherwise known good transistor (provided they are basic transistors with out built in diodes or resistors for example). When you determine and measure the two junctions the voltage drop across the B-E junction will always be slightly higher than the B-C junction. You can of course also determine the transistor polarity (NPN or PNP) by the polarity of the meter lead on the base.

For example: Let's call the 3 pins A,B & C. Again the transistor is known to be good and the polarity of the meter leads are correct. You measure the voltage drop across pin C&B to be .654, C&A measured .656 and the pos+ lead was on pin C. From this we can determine that the transistor is NPN, pin C is the base, pin A is the emitter and pin B is the collector.
 
I have tested my output transistors for my Sansui 7070
(2SC1115) NPN 2 each

(2SA746) PNP 2 each

I tested as EW stated in post #1 and documented all my readings . Everything looks good to me . My question is , do you need to check for resistance from C to E using the ohm scale ? That is something i found online while searching around for testing diodes and transistors.?
 
My readings are as follows checked with diode test Fluke 23 III
2SC1115 #1 transistor
pos neg
b e = .518
b e = .512
e b = .OL
c b = .OL
c e = .OL
A resistance check shows ohms scale , i wouldnt think neg/pos pos/neg would matter . It shouldnt correct ?
pos neg
c e O.L
e c O.L

2SC1115 #2 transistor
pos neg
b e = .506
b c = .501
e b = .OL
c b = .OL
c e = .OL

resistance
pos neg
c e = O.L
e c = O.L



Now the
2SA746 #3 transistor
pos neg
b e = .502
b c = .432
e b = .OL
c b = .OL
c e = .OL

resistance check ohms
pos neg
c e = 14.27 M ohms
e c = 2.443 M ohms this is what i meant earlier about pos/neg neg/pos ?

2SA746 #4
pos neg
b e = .503
b c = .483
e b = .OL
c b = .OL
c e = .OL

resistance ohms
pos neg
c e = O.L
e c = 11.59 M ohms

Do these look ok or are the 2SA s bad ?
Thanks
 
None of those would cause the resistors to burn out on the driver board.The 2SA's may be indicating a little leakage possibly.
 
Well if these are ok to continue using ill reinstall them ? I will now get back to my original thread (Sansui 7070 no sound )in the sansui forum .
Thanks
 
LBPete said:
Or you could bookmark it.

- Pete
Click to expand...

Just how do you do that ? I have read threads before then lost them a week later spending alot of time searching for them again. Sorry if its real simple but ive just never figured out how to (bookmark) a certain thread/post.


Thanks
 
Depends on what browser you are using. Internet explorer click on favorites, add to favorites and give it a name. Fire Fox, click on the star icon on the top right.

- Pete
 
I'll bump this again in hopes of making it a sticky. The info and many references contained in here have saved me a ton of head scratching and increased my learning curve exponentially. How can this not be a sticky already?
 
Or for about $75 just buy one of these http://www.peakelec.co.uk/acatalog/jz_dca55.html and move on with life....

Seems to work great. I like how it automatically identifies BCE, no thinking required. Makes a BIG difference when you're not real sure of the legs on a replacement transistor.

Identifies shorts, calculates hfe...I did find a transistor today that tested good on this meter but under working voltage was bad, but short of building a tester that works at full voltage I guess that's to be expected.

No affiliation with this company, btw.
 
no mention of geranium transistors and expected readings under test . i know they aren't very common these days but they are still about in old gear .
just thought i would mention it .:D
 
Knock yourself out. We're waiting. ;)

Seriously, germaniums have so many issues that precious few devices using them deserve the title 'hi-fi'. There's a number of really good reasons why they're gone.
 
EchoWars said:
Knock yourself out. We're waiting.
Click to expand...

will have to remember in daylight ..it is sat night / sunday morning ..beer has taken over yet again .. :D i will start with the readings will be expected lower ..if i remember rightly
my first amp i built used geraniums .. that's all i had oc71 oc72 .. geranium diodes are ok though for radio .
 
petehall347 said:
will have to remember in daylight ..it is sat night / sunday morning ..beer has taken over yet again .. :D i will start with the readings will be expected lower ..if i remember rightly
my first amp i built used geraniums .. that's all i had oc71 oc72 .. geranium diodes are ok though for radio .
Click to expand...

I grew some geraniums once - they had pretty pinky-red flowers :rolleyes:
 
petehall347 said:
will have to remember in daylight ..it is sat night / sunday morning ..beer has taken over yet again .. :D i will start with the readings will be expected lower ..if i remember rightly
my first amp i built used geraniums .. that's all i had oc71 oc72 .. geranium diodes are ok though for radio .
Click to expand...

I've found they color the sound too much for my taste. :D
 
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