If still having trouble after watching the YouTube above, try this:
From the main screen, press mode to right to get menu and then QUICKLY (will not work if done slowly!) move mode to:
Left-Left-Left
Right-Right-Right
left-right-left
Center-press in on mode, then see the wrench, now you can slow down. Select Service, and then select the engineering menus screens (two pages on my SS9-, move mode to right for 2nd page).
For the Experia is just a little different but seems a little easier:
from the menu select:
diagnostic
With mode switch:
left, left, left
right, right, right
left, right, left
And:
right
(Eng. screen now shows).
-Don- Auburn, CA