I have opened my keyboard 3 times in the past few years due to a minor problem like the flashing SUSTAIN led.
I am amazed at the outstanding quality (control) of the PCB. The cables are laid out nice and connectors are excellent quality.
I did opened it again...checked all connectors...and anything that looked like out of the ordinary. (I know by my experience what to look for.) Put it back together and I powered up. No luck. I still have the problem.
Since this is a computer I wonder if the operating system (program) is corrupted. Any comments ?