Which version and how old? The eeprom in the old Digipac series eventually looses its content. Not all at once but slowly which will cause such effects. Not totally surprising as they must be around 40 years old. Far as I know fixing is now impossible as chips can't be got and Newall never divulged the contents. I eventually managed to get one done about ten years back but it was a struggle then. Later ones Topaz et al are said to suffer membrane keypad problems, some folks say they are not good for more than 10 to 20 years use.
Always worth scrubbing connectors and checking wiring loom.
Heads and bars seem to last nearly forever so you are probably in for a new console. Either Newall, or there is amore affordable alternative from one of other suppliers who do a conversion box to drive the spherosyn and put out common quadrature pulses.
Clive