Tips and Tricks for Troubleshooting
Relei-Blog (in German)
Troubleshooting (device does not boot)
SD card formatting
check if the SD card is formatted correctly. It needs to have two partitions, one FAT and one ext2/3. The FAT partition needs to have a specific setup of number of sectors, cylinders etc. that is different from the defaults! And, the file MLO must be copied as the first file to the freshly formatted partition. Even copying some file and deleting it before MLO makes it unuseable.
check Console output
Connect the RS232 cable and start some terminal program
You should see a "message" like "40W" (OMAP3530) or "60" (DM3730). This indicates that the Boot ROM is starting and using the RS232 interface.
Boot through RS232
To log in either in uboot or in a serial terminal first build the serial cable as described in the user manual. Afterwards, connect the serial cable through a serial to usb converter to your pc. A corresponding device at /dev/ttyUSB0 should appear (consult dmesg). Use a terminal emulation programm such as minicom or agetty to log in using this device (e.g. minicom -D /dev/ttyUSB0). Remember to deactivate the hardware control flow option, otherwise you won't be able to type inside the serial console.