Leaderboard

Doublecheck first to see if any two of the regulator’s three legs are short-circuited (three total continuity tests). If the other rails are good, sounds like it may be a short between 5V and gnd? If you find a short, you may or may not need to replace the regulator; some are well protected and will just start working again while others will fry. If you don’t find a short between two rails...it probably still failed for a reason so probably worth it to triple-check your work (jewler’s loupe can be had for cheap on eBay!) Otoh, sometimes shit fails for no apparent reason and it’s just a bad part that needs replacing. Or sometimes you accidentally shorted something while working and didn’t realize it till later. Or some other freak occurance that borks your work but otherwise won’t happen again. So don’t stress too much if you can’t find an obvious fault. Try replacing it and if it fails again, then at least you’ve established a pattern and have a better idea what to look for. And if it works, it works.

Only had time for a quick test this evening, but yes, there's some continuity between 5v and ground. Now to hunt down the short...

hmm, have to admit I am not an expert here, and the main.asm file is pretty unclear to me too, sorry! this is a probably pretty uninformed idea, but maybe another place to reflow is Q1-Q4 as I assume these are providing the clocks for the shift registers (it's not clear that they are on the schematic but I can't see what else is) and I guess that is something that might be causing the shift register to give the wrong results of button presses? I guess one of the transistors has to be another candidate as they're not too hard to blow.

it sounds like you've done a bit of this, but there is a button/encoder troubleshooting guide here in case you didn't find it already: http://www.midibox.org/dokuwiki/doku.php?id=din_module and a link to a MIOS program to find shift register problems... what are the buttons doing instead of what they should? Or just not operating?