My first and easiest step would have been as you guessed to try another chip. After that I would re-flow all the solder joints both On and Off board as well as joints connected to jacks and power. All of them. I would also check for any wiring on any part of the circuit to have a loose connection perhaps dangling by a wire hair. The entire circuit.
If that does not pan out (and it certainly doesn’t hurt) then as I said there is a lot to check and we would need a lot more info to go on, namely voltages and photos.
This is also a perfect example of where an Audio Probe comes in very handy so you can isolate the problem area on a large circuit board quickly without guessing. There is more info in a PDF and photo we created on the Guides Page
Use the Audio Probe and follow the audio path highlighted in your build document and listen for where it goes bad and you will know where to focus your efforts.