Ah ok, I started to get excited that maybe his pick up was even better than he thought initially.
Nope, just the 601 card which I've cleaned/redone the thermal paste and it's working in my Q700.
So I guess I'm at crossroads here. Attempt to fix the original unit, or replace with a modern ATX PSU and do a conversion?
I've bought a cheap, but what appears to be adequate, Seasonic modular server 400W ATX PSU to use as a way to test the logic board. It may even be good enough for a permanent solution as it has a fairly strong 5V rail and two strong 12V rails. I could hook up a DC to DC converter to create an even stronger 5V rail from one of the 12V rails.
The rough plan is: remove the 40mm fans from this server PSU, use the original Q950 PSU fan instead, hook up a little circuit for soft power, rewire the ATX connector, and re-use the Q950 secondary PSU PCB with the 5V sockets on it to keep it looking stock from the outside of the PSU.
The original PSU is completely unknown to me, I don't think schematics are available, and I don't want to waste time/effort on it.