Solid State Sleuths (Episode One)

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The case of "it looks like a transistor but might be a voltage regulator" 

Some preliminary test results

Spoiler alert: I have no idea what it is

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At this point I think some resistance testing might tell us something

And I wish I remembered reading something about the base collector junction being reverse biased 

Maybe I can assume just arbitrarily designate one terminal as the base and go from there

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Resistance results

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At this point I'm inclined to call terminal one the base
Terminal two the emitter
Terminal three the collector

Time to go look at some books 📚

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Oh well figured I'd try it out

Made up a circuit gonna see if I can apply voltage until there is some emitter current

Was gonna have two power supplies but for now V1 = V2

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Change in plan

I put an LED between ground and emitter resistor

Looks like it works

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Now...idk why a clear white LED turns red when illuminated 

Ok to get a barely detected illuminated LED I have to have 1.7 V at the base and I get 4.2 mv across R3

Yeah I know it's a crap randomly assembled circuit

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I think I might be out of luck yet .

No matter what I do the collector current is about twice the emitter current (voltage drops that is the resistors are the same value)

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At first i suspected the LED but the components are in series so the current and voltage drop should be the same

Might be time to ground the "emitter and see if it behaves like a voltage regulator 

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Alright guys the results are in but I'll wait 

Btw I'll be glad to do anymore testing requested

[g1]

You assumed pin1 to be base, which was a good assumption because (with diode test) it gave you a forward biased reading to both other pins, like a good NPN should.
Now put your black probe to the 'base' and see what the reverse biased reading to the other pins gives.

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Yes sir thanks I did do that but I want to go back and make sure we have all of our ducks in a row

You recall I had one meter that read resistance backwards polarity so I used this other one and just now verified it .

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Now moving on to our mystery component

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As requested

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[J M Fahey]

We need you add the exact same tests with probes reversed.

Full test is 6 measurements, all leg pairs both ways.

As-is it might be an NPN transistor but we need confirmation.
We want to see junction/diode drops (or not, in which case it may be a MosFet)

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Yes sir thanks here goes

Pins 1 and 2

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Pins 1 and 3

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Dos y tres

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