er-100 samsung cash register alarm?

I got this model cash register from a friend (i collect these sorts of things) but i don't really know what i'm doing and whenever i plug it in the screen says E7 770.00 even when the switch is off and when i flip the switch to X or any of the other modes the alarm goes off straight away. The weird thing is when my friend plug it in and switched it on he just pressed a few random numbers and the DPT 2 button and then it would work fine so its a recent problem. I don't want to pay for manuals so any help is appreciated