Inject a 1kHz sine wave into the XLR input. Check if the "Signal" LED blinks. If yes, the preamp is processing audio, meaning the fault lies exclusively within the power amplifier block. 3. Distorted Audio or Weak Output
Contains the operational amplifiers (frequently NE5532 or TL072) responsible for input balancing, subsonic filtering, and the active 1.8kHz crossover split. Power Amplifier Module Beta 3 U15a Service Manual
: Provides master volume, bass, and treble adjustments. Inject a 1kHz sine wave into the XLR input