Per the (slightly fuzzy) picture it is hard to tell if the PCB uses a U designator for the voltage regulator. If so then there is a very high probability Q2 is a transistor and not an IC. The fact that it possibly connects to an adjustable inductor makes me wonder if it is not some sort of oscillator. Might make sense to pop the part off the board and put it on one of those $25 Asian part identifier/testers just to see what it deciphers.
For the parts description on PCB - this i'm sure 100%, regulators are marked U or V, here's Q like other transistors, as stated before.
This is voltage step-down circuit, 12V to 5V converter. One of two 5V sections for logic circuits. Second one is made just with 7805 regulator, this one, i believe, had to be ultra low noise or stable or other reason which designer had in mind. Yes, it is adjustable inductor marked L11, there is L12 fixed inductor at the output too. I tried to adjust L11, but stuck, i'm not sure isn't glued after factory setup.
This section is source of noise, i checked this with oscilloscope.
Here's what i wrote in other thread, checking it with multimeter (not sure it is good as 25$, this one cost something like 250$
):
Checking Base and Emitter it give the constant beeping sound, so it shows that this part of the circuit is shorted. Base and Emitter works as the same node.
Between these nodes and Colector there's reading as for PNP transitor.
B/E red probe, C black probe - shows nothing.
B/E black probe, C red probe - shows reading
Summary - testing was made out of the PCB, it acts like broken PNP transistor, this is the only part in the whole circuit which have strange reading (yes i checked every capacitor, diode, transistor, IC, inductor, regulator and everything else), it's part of the noisy section, so i did my lessons in most aspects of circuit diagnose, in theory and practice. Of course testing burnt parts can show wrong reading, everything says for now it's PNP, but it doesn't have to be. Yesterday Paul "FIX" push me to think that this could be NPN with reversed (non standard) pinout in SOT23, or second option is that this is FET (seen in similar circuits also). If this would be generic PNP, then Q1 and Q2 both rather would be same type PNP SOT23, to cut the costs. Don't see any reason to use two different PNP transistor in such circuit.
