The 12v power supply does not provide power to the head unit over aquabus. Aquabus power comes from the 24v power supply converted down to 12v with the buck converter. I think you actually have two problems here. The 12v PSU is just the more obvious one.
Ah makes sense, clearly much more experience than I. Really getting tired with these things breaking... I've already blown ~$800 in modules in under two years due to failures. Going to reach out to you