September 19, 2012 at 2:22 pm #20888
Is this at about column 15 or 16? It is most likely due to a problem at U5. Check the pins carefully, and see if you can figure out where it isn’t making good contact.
Another thing that you might try (if you can) is to swap the chips at locations U4 and U5, to see if the chip itself is OK. If the problem moves when you do that, the chip probably needs to be replaced.