[eigma] had a difficult problem. After pulling a TV out of the trash and bringing it home, it turned out it was suffering from a troubling boot loop issue that basically made it useless. As so many of us do, they decided to fix it…which ended up being a far bigger task than initially expected.
The TV in question was a Samsung UN40H5003AF. Powering it up would net a red standby light which would stay on for about eight seconds. Then it would flicker off, come back on, and repeat the cycle. So far, so bad. Investigation began with the usual—checking the power supplies and investigating the basics. No easy wins were found. A debug UART provided precious little information, and schematics proved hard to come by.
Eventually, though, investigation dialed in on a 4 MB SPI flash chip on the board. Dumping the chip revealed the firmware onboard was damaged and corrupt. Upon further tinkering, [eigma] figured that most of the dump looked valid. On a hunch, suspecting that maybe just a single bit was wrong, they came up with a crazy plan: use a script to brute-force flipping every single bit until the firmware’s CRC check came back valid. It took eighteen hours, but the script found a valid solution. Lo and behold, burning the fixed firmware to the TV brought it back to life.
It feels weird for a single bit flip to kill an entire TV, but this kind of failure isn’t unheard of. We’ve seen other dedicated hackers perform similar restorations previously. If you’re out there valiantly rescuing e-waste with these techniques, do tell us your story, won’t you?
This articles is written by : Fady Askharoun Samy Askharoun
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