I noticed that most of the time on dead Atari 2600 consoles the TIA is broken. A dark picture will be shown, no sound or ugly lines/audio is provided. Question is why the TIA always die in normal operation condition.

As a root cause most likely it belongs to the power regulator (7805) which also dies first and let power thru the customer chips.  Yesterday it happened during modding of a console. I removed the power cord on the back, the console was lying with the back to the top. I have not noticed that the power switch is still in "on" position as it's face was to the ground. After some soldering work I inserted the power cord again and no video at all.

Damn what was happend? If you look into the schematics all seems to be ok. From experience and knowledge with latest and greatest components. But in old days there is a small difference which you do not know if you have not run into it previously. So after a call with an expert for that kind of circuits the problem is quite obvious and seems to be known in the past - that's why the Coleco Gemini contains this ugly big warning information on top! Yes this ugly black/white sticker with about 10x3cm size on the left side.

Technically the following happens:
The 2200uf prior to the 7805 regulator is already loaded if you have used the console a short time before. So if you connect the power cable the voltage of the old power supply with upto 15V bypasses the 2200uf and as the power switch is in "on" position there is no delay giving the 7805 the time to be ready. So the 7805 passes the full voltage to the output. The full voltage of up to15V reaches the customer chips. Too much for the TIA.
To proof this theory I used a volt-meter and redo. It fully confirmed the theory which now seems to be a design flaw from technical point of view.

A design flaw in the 7805 was fixed a while ago (my expert still remembered) but there are still batches in stock with the bad one and companies still producing the original one. As there was no change in naming/numbering on the 7805 you can't proof the one you are using has the fix included.

Workaround is to add a sticker (like the one below) to the cable so you are remembered doing the right. Or you modify the circuit or power supply. One fix could be to add a resistor prior to the 2200uF or to manually add the fix to the 7805. If it is already there it will not hurt if not it will save your console.

I will add this fix anyway to my modded consoles using method #2 as this also prevents overvoltages in case the 7805 is dying. I found additional information to it in an old book about electronic basic knowledge. Shame! 

My export looked into the schematics and also suggested some additional improvement to stabilize the whole power circuit (like replacing some components after the 7805 which values seems to be too low).