My friend’s SKR E3 mini stopped working and reported ‘TMC CONNECTION ERROR’, the info that came back from an M122 command looked like the X axis driver was dead, googling revealed others having the same issue.
He was supplied a replacement board by BTT, I was given the dead board in exchange for swapping in the new board and reconfiguring the printer.
I removed the suspected dead TMC2209 and swapped in a TMC2208, connected the board to my ender 3 and it works again! Free upgrade!
Many people have suggested the X axis driver failure on this board is due to overheating, likely due to the restricted heatsinking ability of the board – a two layer 1oz board, as opposed to the recommended four layer 2oz board. The reduced copper around the X axis driver due to its proximity to the board edge probably doesn’t help either.
I’ve swapped over the X and Z axis in the configuration as the Z axis typically sees less movements than the X which should help the driver stay cooler, I’m going to monitor the driver temperature over the next few long prints and see how it compares to my old board (also using TMC2208)
Simon's tech blog 