Key board was reassembled, 2 spare keys purchased off e-bay from a seller’s dead unit gave a full compliment of keys to work with.
Powered up the keyboard with new Lithium backup battery installed. All works apart from 4th octave. Found corroded track on key matrix PCB. Also found I had installed a set of rubber contacts ‘back to front’ so the second contact made before the first contact, this really confused the keyboard controller. Swapped the contact strip around, all works fine again.
Keyboard declared functional, but the sound patches on it are really poor, some previous user really had no idea how to use this machine!.
Logged onto the Yahoo Linear user group. Downloaded lots of sysex midi files to laptop. These guys are ‘seasoned’ D50 users who really bring out the best of the Linear arithmetic sound system used by the D50. Uploading the sound patches is easy via the USB to midi dongle.