This is a faulty subwoofer and need repair, after check the pcb, it has been repair trial and see regulator transistor poorly soldered and loose joint. PCB trace on the pcb is weak and need careful repair and touch up all joints. First attempt is power amp board working but oscillation after plug in the pre and crossover boards. Later identified that the capacitors of +/-15V supply weak or not function properly. Thus replace all the E-cap on this subwooder and all working fine. Lesson learn is that Harman use cheap China capacitors and cause the problem not able to last.
