Could you post a clear closeup photo of that chip, and the surrounding area? Most smart phones, and digital cameras have decent closeup capability. Alternately, take a in-focus photo slightly further away using the highest resolution (Megapixlel) setting, then edit the photo and crop it to just that chip and immediate surrounding area. You will basically be doing what digital zoom does.
You can also try contacting Soundtraxx and asking them to identify that chip for you (give you its manufacturer and part number). WHile the odds are low that they will give you that info, since it is an obsolete decoder, they might.
I'll ask again, why do you think that this chip is faulty. Just because it is likely the audio amp? And the problem just occurred spontaneously, or do you think that you might have done something to damage the audio circuit?
Does that chip get hot when the decoder is powered up? It is very, very rare for IC (Integrated Circuit) chips to fail into a cyclical mode that you describe. It is more common for the temperature to affect the chip's functionality. As it heats up, it fails, then when it cools down, it starts working (or vice versa). Or sometimes the chip fails at a room temperature, and works when cooled or heated (or again vice versa). But I have never seen a chip heating up, then cooling down cyclically, when under constant power.
