DSO5102P Rotary knobs not working

Shoey

Has anyone else been able to fix this fault? Seems to be a recurring issue, several threads about this.
I have so far tried:

Default setup
firmware update
self calibration
checked ribbon cable connection at keyboard PCB and motherboard
reflowed decoupling caps
reflowed ribbon connector on PCB
reflowed and later replaced U1, U2, and U3. (74HC393 and 2 x 74HC4051)
checked relay as previously suggested. Actuating fine and connections are good.
all diodes from rotary encoders fine.

3.2V to keyboard PCB from ribbon cable.

None of these steps have corrected the fault. As others have described: all push buttons respond fine, but no response at all from turning any rotary encoder.

Any suggestions on fixes, measurements?