Victor,
All the best with x-ray. Make sure your PLL supplies are fine. If you dont see ddr clk in few more boards, I would think its not solder issue. If you have clkout, probe that to make sure your clock is propagating.
Have a look at this, if you didnt to make sure all supplies are fine.
http://processors.wiki.ti.com/index.php/AM335x_board_bringup_tips
thanks
siva.