I am experiencing the same issue as stated above, except that I am having this problem on two PCBs. Neither of the PCBs will power-up and run correctly. In fact, they both act exactly the same. Vin and Vcc are both within spec with both USB and a 24VAC Adapter. It’s the third or forth time these PCBs have been inspected by me. Unless there is a whisker or ball of solder under a part, these PCBs are good to go. I’m guessing that the µCs in the DIY kit were already programmed before being sold. Since there was a period in recent history where the OpenSprinkler DIY kits were not available, my only option at that point was to buy bare PCBs and source the parts myself. I assembled one OS Pi and two OS 2.2u boards. The OS Pi works great and is currently installed and running. I’m having lots of problems with the ATmega644 based PCBs. Since I sourced all the parts (including the ATmega644), the µCs had no firmware or bootloader installed. After two days of trying different schemes for programming, I successfully programmed the µCs by using an old Duemilanove as an ISP with the 644s in a breadboard with a 16MHz crystal.
I have been through the forum posts looking for anything that might help me. I’d really appreciate your assistance before I pitch these in the circular file and build up a couple more OS Pi’s.