The NAD amp is finally fixed. The ultimate culprit was a bit of rework that had become unreliable. We found the problem by letting the amp heat up to the point where it stayed on, and then hit it with cold spray. This allowed us to reliably isolate the problem to small area of some kind of control circuit board (it had an 8051 clone on it). The picture above shows the lousy rework (Nad, not ours 🙂 The solder blob was heavily crystallized, and reworking this, which included scraping more of the solder mask off of the ground plane to which it was attached got everything going. Yay!
Work still progresses on the PID controller. This is still mostly a software effort. I’ve been mucking with audio and image rendering instead of solder profiles, which is what I should be doing. In the clip below you can see rendering an image from a file on the sd card while simultaneously playing a wav file.