With electric pianos we often see faults with keys not always responding or loosing their touch velocity control, sticky or broken keys. These faults often require the membrane switches to be changed and the PCB bed to be cleaned from hair and dirt. Generally we recommend that if you are experiencing a problem with this kind of fault the best solution is to change all the switches, the majority of the charge is the time to strip down the piano to get access to the key switches and the switches themselves are fairly inexpensive. We change all key switches as if one is failing then generally the rest will be used the same amount and are likely to fail at the same point.
Other faults we see include USB sockets damaged from people tripping over the cables, PSU sockets and jack cables. Basically all the parts accessible to the outside world! It's rare to get faults with screens and CPU failure. Unfortunately if the CPU or memory have failed we're unlikely to be able to repair it as we are a general repairer and would advise you get in touch with the manufacture.