Yeah well, there's a good chance that it is due the cpu.
I've seen it more often with crashes.
Repairing is often not possible and mostly more expensive than buying a new box.

Buying a new motherboard is a option, but the prices are not so interesting to buy it.
You could think of around the 80 euro's.

I would just buy a new 800se box, which depends on what you want.
A Sunray SR4 v2 box with tripple tuner I've seen for around the 130 euro's. while a normal 800se Sunray box cost around the 113 euro.

please pm the website with this price! i think will replace the NAND Flash because i can! but can i change with an other NAND with more memory?

PS: This is the error that I get now when the flash:
21:24:14 Log: +++ 015 bad sector recovery enabled

015 bad sector recovery enabled, is normal, it's just saying that the recovery bad sectors option is enabled.
It only have bad sectors if it says found bad sector while the image file is uploading.

And no, you must use the same nand flash chip, with the same number.
The cpu data does not known other chips, it will not recognized other nand chips.
Same as the memory chips and even the wireless network if it's build onboard.
Also the mini flash button option is programmed into the cpu, with a small part into the bios rom.

See aliexpress, search there for dm800se Sunray SR4