The NX Audio RX 4000 is not a simple Class AB amplifier; it utilizes a high-efficiency Class D topology for the subwoofer channel combined with Class AB for the full-range speakers. Without the correct wiring diagram or schematic, repairing this unit is akin to navigating a maze blindfolded.

Here is what a verified circuit diagram allows you to do:

Before looking at the detailed traces, let’s understand the high-level flow of the circuit.