22. Transistor Identification

Question.3

A damaged BC547 transistor on a PCB needs to be replaced, but only a 2N3904 is available in the component drawer. Both transistors use the small, black plastic TO-92 package and look identical to the naked eye.

What is the important technical detail to check before soldering the 2N3904 into the spot where the BC547 was?

Datasheets (DigiKey)

BC547 Transistor - Digikey
2N3904 Transistor - Digikey

Both are TO-92 transistors, so they can be swapped immediately without checking anything.
The 2N3904 is only for high-power circuits and cannot be used in small signal boards.
The pin order (Emitter, Base, Collector) might be different between these two parts.
Transistors that share the same plastic package always have the exact same pin layout.

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