I have replaced the socket for Gary. When I try to boot the A500 Plus I immediately get a green screen, which means Bad RAM. But it can also mean that the RAM isn't accessible, because of for instance a bad Agnus or Gary. So I rechecked the traces coming from Gary. I couldn't find any fault. As I cannot think of any other cause I will leave the machine for the moment. I might buy an A500 Plus board I saw for sale.