Hello,
Thanks for your reply. Keyboard was not in service, anymore. What I can do, to find source of problem by myself?
Regards,

Pedja.

....Jean sent them a mail about my problem, and technician from service called me. His advice was to bought a set of new cables and change them....

I would do this.

Hello Wildbill,
Thanks for your reply. Did you have some similar experience (with OS restarting) with your instrument?

Hello Wildbill,
Thanks for your reply. Do have some similar experience (with OS restarting) with your instrument?

No.
But I did have some problems with the usb on my le6.
Took it apart and some of the wires looked really flimsy and loose, so I wouldn't be surprised if it was a simple wire problem. A loose connection is enough to cause an intermittent problem.
Maybe not something you would try to fix yourself.

Wildbill,
Thank you very much, for your very clever suggestion, I really appreciate it. I have some problems to bring keyboard to service, but maybe it is a best way to do it so. Thank you very much again, and I wish you all best.
Regards,

Pedja.

Sadly,

I have to say that I have again experience with restarting. I formed a rule, after two years of repetitions in same period (May or June), when humidity rise outside and in the room. That problem lay in capacitors. I don't have time now, to check this (with service men):

https://jirin.web.althan.cz/201705-kurzweil-pc3le-blinking-problem-ultimate-solution/

But, I will finally have to do it.  

Again, last days I had a same issue. One restarting during playing. Two times in few days!

Hi,

I think you need to take that keyboard to service.

Regards,

Fran

Hello Fran,

I hope that you are healthy and good, this very bad days.

Thank you for suggestion,

Pedja.

After a 7-month break, I faced three restarts again, last night. 
I have the impression, although I may be wrong, that the reason for this may be the use of a certain combi on Kronos. 
Since I use PC3LE8 as a keyboard controller for Kronos.
Thanks for your attention.