The same problem happened to me, thanks to this post I solved the problem quickly with almost zero cost:
Suddenly my racks stopped rotating, the motor didn't move. I took out the motor cable, checked the motor with 9 volts and it was spinning, so I realized that I had the same problem with the tank board (the left board from behind). I unscrewed the board and spotted the faulty chip, it's on the top left of the board and has a black heatsink on it that stands out of the board and can be easily seen, the chip is a L4970A ST Microelectronics and can be found easily, it costs around 15-20 euros on ebay. I replaced this chip and I also replaced the Omron Relay (a transparent plastic chip nearby the L4970A) with a new one Omron 12V G2RL-1-E-12VDC 16A 250VAC (cost 3,50 euro) because my electrician suggested it would be better to do so. I mounted the board back, connected all the cables and everything works perfectly now!
Thanks again for the help.