My JR 2720 recently switched off just after launch of my Carbon Miniblade
which rolled on its back and lawn darted. The cause ? the radio gave a long beep and then displayed Backup Error, a lot of discussion on the topic concluded that the lithium Battery on the board had failed .However furthur research revealed that in fact the 2720 does not have the battery and in fact has flash memory and the problem was firmware failure , this means the radio has to go back to Japan to be reprogrammed.And Ive been also told that this problem also can affect the DX7 sets as well. I was also told that it happens on power up ,unfortunately my radio proved that wrong as it was already on. My radio is only 19 months old but still thats out of warranty.
I'm not grumbling about it these things happen this posting is more or less a warning for other users of this radio as well as other check your manuals and if you see the error code BACKUP ERROR listed just keep your eyes open .
Hopefully the reprogramming may upgrade the firmware and eliminate this error happening but thats a big ask I think.
SteveW