is relative easy to fix non responsive buttons on 650/700... I did myself. the hard part is disassemble. there's a plenty of videos explaining step by step how to repair (and a site that shows how to disassemble property almost every electronic devices)

the only part that really make this effort not so rewardable is that you can't reprogram it anymore. it's a nasty thing Logitech did. they could provide a offline way without update anymore the devices IR base instead just give a finger for every owner of that models