Sola UPS 325 (750) won't boot up

I am a retired electronics technician, Swanbank Power Station Ipswich, and have a Sola 325 UPS that has a burnt relay, RY003, on the PCB and will not boot up.
There are no obvious signs of burnt components or leaking capacitors. The batteries are holding charge at 13.75V.
I am looking for a schematic for the UPS so I can trace the circuit around the relay to see what components might have failed to cause the burn on the relay contacts.
The 10A 'car battery fuse on the PCB is OK as well as the mains input overload relay never popped.
Any help would be appreciated. the UPS is about 10 years old and has given good service.
Kind regards, Keith