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Help identifying transistor

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Jwillis:
The package is a SOT23  and a B2H2 in that package is a tl431. On the B2XX the xx denotes 2 more numbers that would be the code that would be printed . and the only other one on that list that comes even slightly close is the B2HX but that is a SOT25.
upon further investigation the H2 could be a lot code so amyk could very well be correct.

magic:

--- Quote from: scatterandfocus on September 18, 2019, 06:45:39 pm ---Can you elaborate on that a bit?  I just resistance tested some 2N3055's using a known good one as a reference, and it seems that resistance testing was useful.  Diode testing didn't tell me anything, but maybe I'm missing something.

--- End quote ---
You will get some result but it depends on which DMM and range you use. I'm also too lazy to try to guess how the resistance reading will depend on temperature and whether it's a big deal or not and how DMM measurement circuitry affects it, if at all.
Meanwhile diode mode is intended precisely for measuring forward voltage of PN junctions and it will show the forward voltage of the junction for some reasonable current such that any variation isn't going to affect the result by much. You can know that if it's something like 600-800mV then your transistor is probably okay but if it shows 400mV then it is likely busted. Or maybe it's a dual Schottky in 3-pin package or whatever.
Moreover, in diode mode you are guaranteed that the red lead is positive and black is negative. With resistance, some crappy DMMs reportedly use inverse polarity and you may end up thinking the junctions are backwards.


--- Quote from: ralun on September 18, 2019, 06:50:03 pm ---Anyone have a way of seeing if it's an PNP or NPN transistor?

--- End quote ---
The pinout of most SMD transistors is as follows:
left - base/gate
right - emitter/source
top - collector/drain

NPN conducts from base to emitter or collector, PNP conducts from emitter or collector to base.

I'm pretty sure it's an IC, though. On the good board, check which pin is connected to ground and what are the voltages on the other pins when it operates.

edit
LOL, an EEPROM in SOT23 and TO92 :wtf: I think I have seen everything now :D

LaserTazerPhaser:
Silk is larger than components in many cases. Soon there will likely be many boards without reference designators to increase part density.

amyk:

--- Quote from: Jwillis on September 19, 2019, 03:27:30 am ---The package is a SOT23  and a B2H2 in that package is a tl431. On the B2XX the xx denotes 2 more numbers that would be the code that would be printed . and the only other one on that list that comes even slightly close is the B2HX but that is a SOT25.
upon further investigation the H2 could be a lot code so amyk could very well be correct.

--- End quote ---
Where did you see that...? From the datasheet you linked, they all begin with "1".

scatterandfocus:

--- Quote from: magic on September 19, 2019, 07:56:21 am ---
--- Quote from: scatterandfocus on September 18, 2019, 06:45:39 pm ---Can you elaborate on that a bit?  I just resistance tested some 2N3055's using a known good one as a reference, and it seems that resistance testing was useful.  Diode testing didn't tell me anything, but maybe I'm missing something.

--- End quote ---
You will get some result but it depends on which DMM and range you use. I'm also too lazy to try to guess how the resistance reading will depend on temperature and whether it's a big deal or not and how DMM measurement circuitry affects it, if at all.
Meanwhile diode mode is intended precisely for measuring forward voltage of PN junctions and it will show the forward voltage of the junction for some reasonable current such that any variation isn't going to affect the result by much. You can know that if it's something like 600-800mV then your transistor is probably okay but if it shows 400mV then it is likely busted. Or maybe it's a dual Schottky in 3-pin package or whatever.

--- End quote ---

That would mean that all my 2N3055's are bad, as all of them are dropping 0.45-0.48 volts when testing with diode mode, which seems unlikely.  So I'm wondering what might be going on here.  I guess it is possible that I had 4 bad 2N3055's on the non-working side of my dual power supply and that I killed the reference 2N3055 from the working side of the power supply.  But it seems unlikely.  So I'm wondering what might be going on here.

Also, I ran across this:


--- Quote ---https://www.androiderode.com/how-to-test-a-transistor-with-dmm/
Transistor BU 208 or 2N3055 Testing
Forward bias:   Connect DMM (+) Test Red lead  to Base
DMM (-) Test Black lead to Collector reading shows = 0.449v
DMM (-)  Test Lead to Emitter    = 0.502v
Verification: If the DMM reading is from 0.502v to 0.449v the condition is GOOD.
Reverse bias:

Connect DMM (-) Test lead to BASE
DMM (+ )Test lead  to Collector reading is = OL or 1 or open
DMM (+ )Test lead  to Emitter    = OL or 1 or open
DMM Reading shows = OL (over load) the condition is GOOD
Verification:  If you get reading in forward bias as 0000 or OL  or 1 or open and in reverse bias as 0000 (or) low values the the transistor can be FAULTY and needs replacement.

--- End quote ---

I would like to understand where these numbers are coming from.

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