can you roughly trace out the schematic?
even if you can’t all the main nodes will be on opamps, the 3 TL074s, and 1 TL072 . Check the pinouts from the datasheets for the output nodes.
If you had an oscilloscope you could look at the outputs. Most computers, phones, tablet devices have some kind of waveform visualizer that can work in lieu of a proper scope. They will be AC coupled but that shouldn’t be a problem here. You could even monitor at low volumes.
If you are careful you can just touch the tip of a 3.5mm patch cable to the output node on an IC. Watch for sparks as you may end up shorting 2 low impedance nodes together, but I’ve not blown many ICs this way. Predictably, the ICs are not labelled. But you should be able to see/hear 2 oscillators, some filters and some stepped edges.
I have seen some parts DOA due to some unknown internal failure.