Midi controller 6 keys don't work (DE24 Alvaston)

This a CME, model UF8 midi keyboard. It has 6 keys not working, those being the bottom three (A-3, B#-3, B-3) and F#-2, B-1 and D2. This is a controller keyboard meaning it has no internal sounds. It is quite old so not the most responsive and some keys that work might not bounce back as fast. I last used it with MacOSx 10.9.5 through its usb port and its midi I/O ports still work. It is very heavy at 23.5 kg. It will run off usb power or a 12v 1A power adaptor.