The controls were erratic. Using the input test in the diagnostic menu I could see 3 buttons and the right direction were being activated together.
A visual inspection quickly pinpointed the fault. One of the input resistor banks was partially desoldered and cracked.
Trying to remove the IC myself proved quite a task but removed the two parts and slotted in a 4.7k resistor array from a scrap board. Now the inputs work fine.
Just need to find a sound board for it now.