One quick and dirty way to narrow down the problem area is to purchase a can of electronic freezer spray. If you use this with the narrow straw like applicator that usually comes with spray cans you can "freeze" individual components to see if the TV restores to normal picture. Do not flood the area, be sparing in how you apply it. You are trying to isolate the problem component.
Initially try to determine whether a component is "hot" or just warm to save spraying too many components. Place the back of your hand close (definitely NOT TOUCHING ANYTHING) to get an idea of the radiant heat being given off.
BE SAFETY AWARE! THE TV IS "LIVE" DO IT WITH ONE HAND BEHIND YOUR BACK (only half joking - that way you will not have one hand accidentally touching something live - which is bad enough - and the other touching something else that you shouldn't)
The ones covered in metal do run warm/hot, that is why they have heat sinks to disperse the heat. Remember electronics can run warm and even hot.
It may be trial and error but then again you may get lucky.
After freezing the correct component, the TV should behave normally. When the effects wear off it will return to being faulty so you can determine by freezing it again whether you have the correct one or not.
It might be prudent to have a mirror in front of the TV facing to the back where you are working. That way you only have to look up and over (or around) the TV to see if anything has happened when you spray.
Here is a link to what I mean. You may have to source something similar from your local electronics shop.
Do one or two components at a time, give it time to have an effect before moving on that way you will not be confused as to which one may be the problem
SAFETY FIRST! Remember to disconnect the power before touching anything in the back of the TV