A105 Germanium transistor wanted.

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#21
I think I know these transistors, A105, A114 ... a.s.o. they are often found in industry controller boards. Type is indeed KRA105M and marked A105. They are PNP but with built-in bias resistors to interface directly to a microcontroller output. (see the attachment).
These resistors fool your ohm meter indicating a faulty transistor but you simply measure the resistors.
And if you don't know what else connects to it you cannot test a component in situ except for a dead short maybe.

By the looks of your board, the transistor may still be O.K. but the smutch may be conductive and cause the problem.

I would solder the transistor out, thoroughly clean *all* the dirty areas on the board, test the transistor with the bias resistors in mind, and if its O.K. put it back in.
 

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#23
Solved! Good on you mate! I should have known this because I've come across these transistors before, I still have some A144, etc... but my memory is failing me as I get older. The transistor measured up ok so I'll clean the board up properly and see if it works? What threw me off was the difference in the size of the case, usually, these internally biased transistors are smaller? Thanks again! 😀
 
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#24
Sorento said:
I think I know these transistors, A105, A114 ... a.s.o. they are often found in industry controller boards. Type is indeed KRA105M and marked A105. They are PNP but with built-in bias resistors to interface directly to a microcontroller output. (see the attachment).
These resistors fool your ohm meter indicating a faulty transistor but you simply measure the resistors.
Click to expand...
Cool!!!! Great info!!!!
I wasbaffled by the description "digital transistors" but now I understand.
A regular transistor would "work", sort of, but BE diode would clamp/short microcontroller; resistors avoid that.
 
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