how do you remove the display lcd panel for the temp?

Go to YouTube and watch a video on how to do it.

LCD's use a conductive membrane between the glass and the case. The contact is made by pressure (on smaller LCD's a bezel snaps over the glass to maintain pressure) ... sometimes if the display is subjected to large temperature changes , over time the expansion/contraction effects the bond and pushing on the display results in some info coming on the screen ( like half a letter or number) Sometimes a display will be visible when it's hot but not when it's cold. I doubt you have a bad cable or external connection. I'm a certified instrumentation tech and this problem is very common on older displays. Of course I could be wrong but ,,,,