I was worried that the 10V magic smoke adventure from the weekend had killed my display... a quick test showed that it worked, but I didn't do much more than 5 seconds to see if it showed something.

Last night, after re-soldering the entire controller board for a third time, (this time verifying the operation of the linear regulators before soldering them on), I was able to verify that the display works. There are still some problems somewhere; I suspect the issue is the DACs (which, given that they are MSSOP-10, I have been unable to verify without soldering onto the board), but I uploaded a simple display test program (seen below) and you can see that all characters are showing properly with no errors or artifacts.

Tonight I hope to have time to verify (and replace if needed) the DACs, and (finally) get the controller working.

One more note on the ISP issues: on this go-round, I decided to not populate the pullups / caps / TVS diodes on the encoders (which are shared with ISP pins). Those are the root cause of the ISP problems, and instead of putting them on the board I can solder them directly to the encoders. It is a bit more annoying, but perfectly doable, and will allow me to re-flash using the ISP if needed in the future.

Cheers