White Rectangle on TC-P55ST50

Several months ago a power surge during a storm apparently fried the "A" board on my 7 year old Panasonic TC-P55ST50. Interestingly, the HDMI ports failed first, but the TV was usable using composite video input for a couple of months there after, but the whole picture disappeared suddenly. Given the 13 flashes from the power indicator, I decided I needed to fix/replace the "A" board. Purchased a used "A" board on the net and installed it. I now have reception and a clear picture, but HDMI ports still do not work and I have a white rectangle covering about 35-40% of the right side (as you view) of the screen. The white rectangle also has light gray wide horizontal stripes that seem to change in width. These stripes are confined to the perimeter of the rectangle.

Has anyone experienced white rectangle covering a large portion of the screen ?

Any ideas what the issue may be (bad "A" board, other faulty board or a poor installation of the replacement "A" board) ?

Thank you in advance for your ideas