With your symptom I assumed it is a plasma. A quick Google confirmed that. An LCD power drain is just about constant unless it is one with contrast en hancement by dimming the backlights selectively, which I think is cheating because it only "tests" better. Anyway...
When you increase the brightness on a plasma, two supplies are generally lo aded harder, Vs and Va. You will see pots to set these voltages and test po ints for them. On a sticker on the PDP itself is usually a specification to set these.
I would guess that one (or both, depending on design) of them is dropping w hen you increase the brightness. This is interpreted by the circuitry as a short circuit or overload and it will trip the safety. It will shut down.
Most likely you have caps on the power supply with high ESR, in some cases it might be a transistor, depending on how it is designed.
Anyway, when a plasma TV has a broken PDP display module, if it gets turned on it can blow the power supply due to overload. It can also blow the sust ain boards, or at least the Y buffers, which are the most vulnerable. If yo u ever break one or buy one broken, unplug the panel before turning it on t o see what fires up.
At any rate, you are most likely looking at an electrolytic cap with high E SR. I would measure the Vs and Va, and some of them have a Vg or whatever. These suppies feed the sustain boards on the sides and sometimes the long b oard at the bottom (and sometimes top, but not in newer models). These volt ages need to be rock solid. It is most likely a source feeding the side boa rds though, they are the ones that pull all the current.
Check ALL those higher voltages. Usually one is like 100-120 volts, another will be like 85 or so. They could be less, go by what the sticker says and if they are off, DO NOT TRY TO ADJUST THEM. Fix the problem and then check them.
If, once the thing works, check them again and if they are off, note just w hat voltage is there on each, and I mean with a good digital meter. Note th e picture and observe some dark as well as bright scenes. THEN adjust to sp ecifications. Before and after you are looking for little flecks in the pic ture (probably green) and any "pastey" looking bright areas of the picture.
Generally the lower voltage is better if all else is equal. Once in a great while they have to be adjusted off spec., and that usually means lower. If someone adjusted it this way, leave it lower as long as there is no differ ence in the picture.
The reason you want to avoid screwing with those voltage settings is becaus e temperature is involved. As the PDP gets hot, its requirements drift a bi t sometimes. Special test equipment is used to determine the exact voltages required for each individual panel and it is not that simple.
Hey, at least you don't have to do convergence...