Help! Rock64 won't boot anything!

[z4v4l]

I think your board is not broken. UART output you get, most probably is a result of baud rate mismatch, rockchip socs use this crazy 1500000 baud/s rate, i never managed to really use it with any system connected as a terminal. that is, the board prints info into it, but it does that with that uncommon speed, whereas your receiving port handling software thinks it's normal 115200. may be that. so, first what you need is to establish serial output. you need to ensure your adapter (and its driver) does support 1.5Mbaud/s rate. the problem with the board itself may be in that, there is something in SPI flash, and that something pooped its pants, stuck and preventing you from successful boot out of sd card. unfortunately, I don't remember how, but you could try to disable SPI, by shorting some pins on the header during boot, search for it here, in the appropriate forum, try it with a guaranteed properly prepared sd card (with uboot etc) inserted, of course. if that boot is successful, you can properly and certainly erase SPI flash from that linux session and have troublefree boots next times.