Help identifying SMD Component - Vehicle Audio Amplifier

[ryann]

I'm trying to repair my Rockford Fosgate P300-10 amp+10" sub that I've had installed in my car. The fail-state was remote input started outputting power, which kept all my accessory power components on (around 8V), and the amplifier remained on all the time.

I believe I've narrowed it down to a transistor. The SMD code is 2TN. It's in a SOT23 package. What I believe to be the base and emitter is shorted with 4 Ohms of resistance, either way I measure it. I'm taking a stab in the dark (only debugged do far for an hour).

I have attached how I think the circuit works. Q1 is an guess at what the component is, since I have not been able to identify it. T1 is acting as a diode. It's an NXP BCP56 NPN diode.

The problem I've identified is between TP1 and TP2 in the schematic, I measure 4 Ohms, no matter the direction I measure, meaning to me, that the transistor has failed. I have removed the transistor from the circuit and applied power back to the circuit. The amp remains off (good thing).

So, I am naively hoping that replacing Q1 in the schematic (SMD part 2TN) will fix it. Problem is, I cannot identify it. Any help?

[ryann]

That transistor was just the tip of the iceberg. I moved another 2TN transistor from one of the other Auto Power On switch inputs and it still turned on without any REM input.

[jkf1000]

Thr REM input from the vehicle is normally active high. The schematic as it is drawn would not operate unless the diode was in the opposite orientation unless I am reading something wrong?. Karl