Kurzweil 2500SX not working Ribbon Controller

[swingmusic]

Hello dear friends!
I have more than 20 years Kurzweil 2500SX 88keys. I serve him all the time (independently).
Since there is no Kurzweil service in my city. I have established THREE SCSI HDD inside and a Cd-ROM. KDFX, sometimes I have to deal with replacing Knobs on the front panel...............and other stuff...

Well............yesterday I noticed that Big Ribbon Controller does not work! Wou! I was very upset.

I immediately did a Hard RESET. Alas............nothing has changed. Big Ribbon Controller >>> It's not working.

I raised (opened) the upper panel. Examined all connections of wires. It's okay. Then I even inspected the wires with a tester ( the wires going to the unit Pitch Pend). It's okay. Hmmm........

Small Ribbon Controller >>> works fine.

I need your help and advice. And I would be very grateful.

Thanks