At least in my TV, the metal backing seemed to be the ground. All of the circuit boards were screwed into metal scaffolding which in turn was screwed to the metal backing.
The ground connections on the circuit boards were obvious. It’s basically where the screws connect the circuit board to the metal scaffolding. Here’s a close up of the top left corner of that orange circuit board:
0_1491098823961_ground.JPG
When the screw is in place, it makes contact with that bear-claw looking piece of metal. My understanding is that the various diodes, capacitors, and whatnots ground themselves through that. So, when I used those little plastic standoffs and the screws couldn’t reach, I used the wire to make the connections. If you can find long thin screws, they may work, too. I didn’t ground every one of the screw connections, just as many as I could. Seems to be enough.
The standoffs I bought were easy and built for this purpose. They have adhesive on the bottom, so they stick to the metal backing. Make sure whatever you use is non conductive.
I had to use wire to ground the orange power control board and the large green boards on the right (2 boards, but they’re connected).
The little board at the bottom is exactly as it was when I opened it up. If you zoom, you’ll see that the grounding screws in each corner connect to a little hill on the metal backing. That way it grounds, but keeps the circuits from shorting on the metal.
The board on the left controls the light panel. That one is also left as it was also.
Basically, if you remove enough of the metal scaffolding, you’ll need to make sure you: 1) keep the underside of the boards from touching metal, and 2) ground the boards somehow
Again, this was MUCH easier for 24 inch TVs. Also, - take pictures as you take it apart, so you can reference them later
Good luck!