GE Oven not responding

[Dima]

Have GE oven model CT9050SH1SS which is non-responsive to key presses.  At start-up it shows 2ER2 which I thought was an error code but not finding it on attached Tech Sheet.  My initial thinking was it is control board WB27X25554 which I replaced but there was absolutely no difference. I am now suspecting either glass touch panel WB56X23723 or UI board WB27X23724 which attaches right to the glass touch panel and has the clock on it.  

Thing is that main control board, UI board and other boards as WiFi are all attached by 3 same wires which suggests these communicate digitally - so I have no good way to confirm which board (as I suspect) is a bad one.  Tech sheet states to enter Service Mode, need to press and hold keys 1 & 5 for 3 seconds after initial power up - I get nothing no matter how I try.  

Can anyone help?  Any suggestions?