@stewiee intermittent errors hare the hardest to find out. Could be originating from the main board but could be an issue on the panel drivers. Check for any components that may look "{different" Odd compared to the rest. Check the solder connections (check both sides of the boards. The solder should be shiney and silver dull and grey appearance could be a cold solder joint. This is one of the cases where I would try some freeze spray. Once the lines appear use the freeze spray and use it on some of the IC's on the main board first. See if and where it makes a difference. That should help you determine where it originates from. Not an easy task and it may take a while to find the properly part.