Panasonic TX-51P100H rear proj tv red covergence problem

Hi all, I have a Panasonic TX-51P100H with a red convergence problem.  If you put a crosshatch pattern on the screen the red crosshatch is quite distorted in the bottom left hand corner of the sreeen and to a lesser extent the top right hand. After the tv has been on for a while the covergence is ok, but then then fails again. I have read on other posts this is to do with convergence board faults.  Have been an elactronics tech for 28 years...mostly worked on CRT tv sets....hope someone can offer me some help with this fault.