Troublshooting TM-1, Power Supply or Spindle Amp

Hello,
Have a TM-1 (2000 vintage) that we're trying to resurrect. Battery died. Lost marbles. Battery & marbles replaced.

X,Y,Z home and jog fine.

When I try to spin up the spindle, say 500 RPM using M-codes, it will cut out unless I start at 100 RPM and increase incrementally by 100 RPM. Using this method I've gotten it up to 4,500 RPM but will not increase above that.

Alarms thrown are 123 Spindle Drive Fault & 292 320V Power Supply Fault.

Looking at the spindle/servo amplifier (4017C) the fault LED isn't lit.
The 320V 5HP Power Supply shows "d", overload/short fault.
Spindle is noisier at certian RPMs than others, every 400-500 or so. For example, spindle sounds awful at 300 RPM but pretty good at 400, like wise 1500 & 1600.

I'm kinda leaning toward the spindle motor rather than the power supply as X, Y, & Z have no issues. Could be the amplifier.
I just don't know.

Any help would be appreciated.

Thanks,

HR