Keep the lid off, or you can raise the rear of the lid about an inch or so (after the screws are out). Note that the heat sinks near where the line cord goes in, have some voltage on them.
If you do remove the lid the cooling problem is quite apparent. The cooling fan for the CPU isn't aligned with the openings in the lid. Also the power supply (which gets very hot) doesn't have any ventilation openings.
I had sent the TU-DST50 back to Panasonic, because the picture would break-up after several hours of operation. When I got the unit back, I saw that they had used foam tape and a sheet of thin plastic to make a "duct" from the fan to the opening in the lid, and they had reversed the fan. Previously it blew down over the CPU, now it blows the heat up and out thru the lid openings. The unit still gets hot from the power supply. Additional holes in the lid would help.