Toshiba 42SL738G - switches itself off - loose screws and potentially bad solder joints on power supply board

A friend got this TV from eBay classifieds. The seller said that after about 1h the TV would switch itself off.

A TV switching itself off when it is warm has either a problem with cold solder joints or some semiconductor is flawed. I didn't waste time waiting for that event and opened the set right away. First thing I noticed was the fragile plastic case. Not impressed.

Toshiba did not use any adhesive tapes here, applause for that! However, the power and logic board (the green in the center) were so ill-fitted to the chassis that they bent. Look at that:

Jesus, Toshiba! Seeing this directed my attention to the power board, which might have had a problem with cold solder joints. I did not see any obvious cracks on the joints of the FETs and diodes, nevertheless I re-soldered all of them, just to be safe.

None of the FETs and diodes had rivets in their solder joints. Boooh! This is very cheap and prone to fail eventually.

I also noticed that all screws besides the one of the backlight board were loose. This can cause problems when a ground screw is affected. It can even kill a TV (see Panasonic Plasma loose screws)

After tightening everything up, I let the TV run for half a day and a couple of evenings and it was flawless. At least electrically. The image suffered from the "dirty screen symptom". Look at the vertical, regular streaks:

They appear in regular distances, yet in alternating intensity. First I thought there was dirt in the panel, like it tends to accumulate in panels with CCT backlight, due to electrostatic charge and heat. However, in an edge-lit LCD TV there is neither of that. After some research I realized that this seems to be a well-known issue among all brands. The reason is the hunt for ever more contrast and dark blacks, which require aggressive filtering. If the filter foils in the panel do not perfectly align, those patterns appear.

This TV is a mixed bag. The image is quite ok, but suffers from the dirty screen symptom. The sound is very thin. The overall build quality is mediocre.

Considering the cheap price my friend got it for and the 0€ repair, this doesn't matter much.