>>3631891There's some truth to that too but the 5D was notorious for that.
Drop the bottom plate you'll need a jewelers screwdriver. After that, the back plate comes off, if I remember the screws for it are under the rubber grips. It's pretty straightforward. The ribbon cable for the LCD I believe is on the bottom of the LCD and you should be able to power it up with the covers off so you can test it.
The 5D is built like a brick shithouse but that was 15 years ago.