Screen image jumping and flashing. Backlight OK

Hi guys, just got a MBP with this issue, image attached. laptop was working fine(according to the owner) but it was getting high temperature working with SeratoDj. The guy opened it and changed the thermal paste. after that computer powers on and no image.

He bring me the macbook and I disassembled it completely looking for something off, it was pretty dirty, I cleaned up and and change the thermal paste for other more appropriate. Now the macbook powers on and sends image signal to the screen, but the image is jumping continuedly and moving, showing only sections of the screen, that moves. The macbook works OK with an HDMI external monitor, I don't think is the screen for sure(it could be). No bumps nor hits on the screen. Logic board model is 820-00138-A, I look it up online and found some boardviews files but they are not the exact same as the board, pretty similar, but not the same. Don't know really where to look or test XD. thank you in advanced !