Same Symptoms. Different problem -- a bent pin.
The first time I powered up, the the LCD didn't light up. Panic.
--Didn't see a light on PSU or on Rambo board.
---Finally did discover the green light at the top of the Rambo. The case has to be open and you have to look at the right angle to see it. Never did find a light on the PSU.
---Tech support (chat) person suggested trying all permutations of the LCD cables until I found the correct orientation [From the suggestion, sounds as though you won't destroy any components regardless of the LCD cable orientation. Many thanks to whoever designed the circuits with that foolproof feature.]
---After many cable changes I finally noticed that one pin at the top end of one of the Rambo connectors was bent outward slightly. Because the Rambo case is so cramped, I didn't notice that the LCD cable was not seating all the way down. Gently straightened that pin by pushing it with the screwdriver (thanks Rambo for using connector pins that don't just snap off).
Powered up and the LCD now displays the "calibrate" message.