Q: condiction:
1.the supply is powered by the 5V adapter-OK
2. the OMAPL138 has been plugged in the baseboard
3.without anyother connection
Phenomenon:
1.D5 doesn't light(3.3V-1.8V OFF)
2.R169 is low
A:
1. D5 should light up with or without the SOM properly seated.
2. R169 should be otherwise you would be asserting reset.
Are you seeing any output on the terminal?