This is not quite a solution but I found that when we wait for some hours, the problem dissapears itself.
I know nothing about electricity but it's a bit like if there were some condensers that need to be emptied.
When that problem happened, I let my TI2 on by chance for a night and everything was back to normal the day after ???
Problem occured several times (until I noticed that my shoes were involved :-))) so if you plan to play on this keyboard, just buy the whole set of PC technician (antistatic pad, wire to the ground, etc...). Nice look on stage !
This situation is not extraordinary when you open your TI2 and look at the power supply. It's just a sort of phone power supply put like this on the chassis with some sort of glue. Pure shame for an instrument of this price ! Of course, no ground but that you can guess when you see the power cord !