If it ain't broken, don't fix it. Specialy a mainboard upgrade is a bit useless and might fail. It's very timing sensitive, changing the more advanced settings in the bios other than default often makes the system hang. My NT4 system had errors that I could not repair with the standard install cd because it was a high security version (that made me smile), no USB support, obsolete network and a terrible user interface. I have upgraded CPU, memory (windows really likes that), networkcard and a extra USB card to create a bit of extra head room for a "newer" OS. With XP running it's just a bit more user friendly but not a better scope. If you are happy with your W2K install, just leave it.
Because this is a little bit difficult to accept for us explorers you can also add a second scratch HD and start experimenting.
For the search enigine archives:
The PSU in the Ultima is a third party Ferrus FP250-710. Itś a low frequency (36kHz) push-pull smps with 3 separate switching circuits on a common PWM, 7 output rails at 700W max total.
A real pain in the nose to work on, no schematics, no info, compact, components hard to reach, testleads don't fit or hitting other components and because of the layout of the 3 circuits on the baseboard no clear separation between prim. and sec. So most of it is hot and can bite humans and equipment pretty bad what made live testing a bit tricky.
My PSU was very dead, no output, not looping in startup and no visible damage. First thing: check primary, all ok DC present. Next: gate signal at the regulated startup rail, present but low and not a happy PWM, at least not enough to pull the FET open. That signal comes from a driver transformer which is just a small ring core with 3 solid wire windings, not a real failure suspect. So I started chasing a short of some kind that pulled the PWM down in the other circuits.
Driver circuit second switcher, OK. Third switcher OK, feedback OK. PWM circuit: SG3525 fully functional but output weak. This is a common old age thing where the open collector output drivers are getting leaky, higher voltage drop, lower output voltage and some extra heat that accelerates this proces. Chip will fail in the near future, specialy if it drives the transformer directly.. Simple fix, just replace. Now with the PWM on level again i'ḿ back to starting point, but this time on the primary side of the driver transformer. Desoldering it's leads, check: open .... shoot.
Easy fix: made with a piece of wire a new primary winding on top of the other, and with this it came back to live.
Next big question is how is this possible? The 100mA running can't even scratch that wire so it must be a combination of thermal and the ultra-sonic coil beating.
PSU fact: it has a small 12V standby DC/DC supply that is powered from the main bulk capacitor. Without powerswitch the complete primary is always on including the divider/bleeder resistors. That explains the 15W standby power usage.
For the calibration i will try a "smart" approach with compairing the files of the old with the new (and yours).
A bit long weekend story, salut