This kind of issue can happen if the very delicate FFC cables on the
LCD screen are damaged. As they are so delicate, even slightly
mishandling it when you opened the set can cause it.
Sadly, replacing the LCD may be the only option.
It may be possible to delicatly shake the FFC cables to figure out
if it is loose contact, and then use Silicone glue to hold it in place.
Another possibility is static damage to TCON board during your repair.