Motherboard status leds are controlled by the cpu and the behavior could be different than the older receivers due the difference of programming which is programmed into the cpu.
In any case, I can not tell if it says something.

But..
1. without the tuner does not help.
2. No wifi either.
3. Memory Test indicates that it is good.

What remains is ..
Nand flash chip, upload an image file with bad sectors recovery enabled, and see if it has bad sectors ..

If not, then it may be a poor/low voltage output of one of the DC to Dc IC's.

And otherwise, it is a more difficult, probably a not be solvable problem as a problem with the cpu.
This is not repairable because the appropriate cpu's are difficult, most likely can not be found.
Older dm800se cpu's won't work on the newer (Sunray/Estar) motherboards.
They are different programmed and locked for reprogramming.