This is the way I wall mount a plasma or LCD TV on a plasterboard wall.
Firstly fit the tv bracket to the TV, ignore the wall mount part at this stage. Follow the bracket manufacturers instructions on what screws to use and use any washers supplied. Make sure the screws are tight but not over tight. The brackets I use are the long rail type which will most likely span two beams in a stud plasterboard wall.
Next decide where about on the plasterboard wall you want to mount the TV. Mark the center position on the plasterboard wall and a line where you want the bottom of the plasma to be. I use a spirit level to do this. If you are mounting it over a fireplace mark the middle of the mantelpiece and use the spirit level to take the line vertically up to where the center of the wall mount will go. To get the height of the wall mount, measure from the bottom of the plasma screen to the top of the “hook” part of the TV bracket. Now transfer that measurement to the wall. Measure from the line where you wanted the bottom of the screen to go to the distance you measured. This will ensure you get the plasma TV at the height you wanted it to be.
Now offer up the wall mount to the center line and the measured line for the height. Using your spirit level to make sure the wall mount is straight. Mark the holes on the wall.
There are two types of plasterboard wall. One is “dot and dab” where the plasterboard is stuck to the blockwork using an adhesive. The other is stud wall. You can tell if you have dot and dab by tapping the plasterboard wall. If there are solid sounding parts of the wall about 600mm apart then it is dot and dab. This is the preferable place to drill the holes. The reason for this is that when you tighten the screws the plasterboard doesn’t pull in and crack. Normally if the bracket covers a couple of these solid bits then you will be OK. Make sure you fix the tv bracket here. If the TV bracket doesn’t span two solid dabs then maybe you need a professional!
If the plasterboard wall is a stud wall, when you mark the tv bracket holes hopefully you will find at least one studs to fix to and therefore take the weight of the plasma or lcd. One is usually enough to take the weight seeing as most flat screen TV’s are so light these days. Put a couple of extra fixings in anyway to stop the bracket slipping out of level. I normally use the butterfly type fixings for this. Make sure you have a least a couple of fixings into the wood though, if the wall was to get wet from a flood or leaking pipe and you didn’t have fixing into wood the plasma or LCD would hit the deck!
When you are sure you have good fixings and the wall bracket is level you can hang your TV up.