Multi-node SGI Onyx2 startup help

Greetings; Long-story-short, a couple of years ago I picked up six Onyx2 racks and have been moving them around with me without ever actually firing them up. I've finally got myself sorted and have been slowly working through bringing things up and having some successes, but every step closer has me finding a new problem. My set-up right now has one graphics head and five compute nodes cabled together in a daisy-chain (not enough CrayLinks for anything else). It appears all but one of the MMSCs are shot, so I'm doing manual start-ups using the keys. My current confusion is how to nominate which system becomes the Global Master. For some odd reason whenever I bring up three racks the machine I've "picked" as the master (keyboard/mouse/gfx head) comes up just fine and boots into IRIX, but whenever I add two more nodes things get a bit more fuzzy and the Global Master appears to migrate around. I had initially believed that the last rack in the power-up sequence would always become the Global Master, since it goes and finds all the rest, but this apparently is not the case... or perhaps there are corollaries I'm unaware of. The more times I turn this thing on and off the more hardware is failing on me, not unexpectedly. I've lost a PSU, a node board and now one of the racks has started making a worryingly hot-electrical smell. I'd really like to get it all working together just once before I get old and grey. Cheers; - JP