Mysterious rtVAX 1000 Failure

I have started playing with the rtVAX 1000 I collected last year. It was running OK when then was a sudden bang and the machine stopped. Not even the fans will run. There was no smell and no smoke, so I knew immediately that it can't be the mains filter capacitors, which always fail on these power supplies. I have opened it up and cannot see any damage in the PSU, the CPU, the memory, or any of the other boards. I am sure it must be the power supply, but I really can't see any damage. The power supply is one of the ASTEC ones common in the MicroVAX II. My first step is going to be to test the PSU with a dummy load using light bulbs (still haven't built a board for a dummy load) and with the fans connected, but nothing else. Will also check for ripple at the same time. There are two outputs from the PSU that I don't fully understand, one is P OK, I am guessing that means *something* is OK, but not sure what, power perhaps, but what power?. The other is called LTC, I have no idea what that one means. Can anyone enlighten me? Any other ideas? Regards Rob