I think the shells vary. The one I bought was fine on the outside. On the inside, though, it was significantly different. Enough to make it non-compatible in relation to the amount of effort I was prepared to expend.
I would hazzard they didn't do it that well?
Maybe I'm being unfair, but this is pretty simple. It's a heating element. You want 12v at one side and 0v at the other. If you're not getting the 12v, the problem is somewhere else. If you *are* getting the 12v, maybe you're not getting the 0v. If you're getting both 12v and 0v in the right places, then the screen's (still) ******.....