Opens dark, can see logo and screen with flashlight, keep jumping

I had a situation with my led screen wherein the brackets surrounding the back cover were broken. I purchased a new back cover and attempted to move the led screen that was still working into the new backing. Upon attempts at hooking up, LED screen no longer worked. Instead the screen opened black and although you can see the apple logo appear very faintly, it jumps up and down upon start up and even when the desktop appears. I purchased an new led screen and main cable but the condition is the same. When I turned on the screen for the first time, I though I smelled an electrical burning smell, which I though might have been the led screen. After research I learned that there is a backlight chip on the motherboard. If it was burning out, would it make the burning smell I detected. I have used a service that could replace motherboard chips. How can I determine if the problem is the backlight chip. The fact that the apple logo keeps shifting position makes me concerned that the problem goes beyond the back light.