How can I fix my Stoves 600CTH halogen Hob?

My hob will only with one ring on at a time. If I try to use 2 rings, 56 flashes and then the switches off, this applies if I try all four rings.
Two years ago I had a problem where the hob would not switch on, and only 56 flashes. I fixed this by changing the capacitor C17 to a 1000uf 16v which fixed the problem. With this new problem I replaced the capacitor again, but without any success. Does anyone have any ideas what could be wrong.