The manual allowed me to reprogram and test the computer before sending it back to my friend. Although this operation is not explained in the manual, I had to repair the defective + pushbutton. If you remove the four allen screws (not the ones that give access to the battery compartment) that hold the case together, the case comes apart in two halves. You can see all the electronics (sealed by the usual Mares gel), and also get access to the three pushbuttons. Pulled up the deffective one, it comes apart real easy, cleaned the debrie that had accumulated with time thus preventing the embedded magnet to operate the reed relay inside the electronics.... and voila !! the pushbuttons worked again.