Can't see audio waveform of the boombox

[Waion]

I’m trying to measured the output power of a boombox before the output signal gets distorted.

I input 100Hz 0dB sinewave via Line-in socket. I don’t see any sinewave at the speaker +ve and -ve terminal. But I can hear 100Hz tone from the speaker.

I use oscilloscope to monitor the output waveform. Confirmed my scope and probes are OK.

Picture below is what I got from the scope. This waveform is the same all the time no matter I increase or decrease the boombox volume.
Also no different if I change the input frequency (vary from 100Hz to 20kHz).

I want to see the output audio waveform. Can anyone help please?

Thanks in advance.

 

[OldDIY]

Class D without filter? Which chip?

 

[Waion]

DLS4110A, 8-pins SMD. I couldn't find datasheet from the internet.

 

[OldDIY]

Carrier frequency (or self-excitation).🙁

 

[Waion]

Carrier frequency (or self-excitation).🙁

I need to make a output filter in order to see the audio waveform?

Picture of the chip (DLS4110A) attached.

 

[OldDIY]

9v 1a - 2w