K2625 calibration

Good evening,
The assembly of the k2625 is done. First check with 12 V is OK, but I cannot run the calibration :
I’m using a transformer with 12 VAC output, plugged on the “-” and “IN” as described, but nothing happens.I tried to adjust the RV2 without success. Does the display work with only “-” and “IN” plugged ?
What about the “+” ?
I tried to use it on the car and it works, but I don’t know the accuracy of the information because the calibration is not done,
and I want to use it to tune the engine as well as possible.
What is wrong in my operation ?

Thanks in advance for your help