ATAG Gas hob GKC 411 OE

In the spirit of the Repair Shop … My mother has an ATAG gas hob GKC411OE. I believe this hob was purchased in the early eighties. The gas rings still work flawlessly but the electric ignition system has failed. No sparking from any of the 4 burners that makes me think it’s the ignition spark generator unit (mains supply and electric plug are fine, ignition plugs all look good and clean).
Does anyone know how you access the ignition spark generator unit? I assume the idea is to remove the burners and lift the top of the unit but the burners are not fixed with normal screws. I am not sure if it needs something like an allen key? Any thoughts?
Assuming that the spark generator is accessible am I likely to be able to source a generic replacement. The hob has an ignition button to generate sparking. Nothing clever on the burners.