Desktop has windows 7, but the machine is air gapped...

I got the machine working. I had accidently plugged the Z limit switch cable to the wrong plug.
Now however, the spindle is making more noise than I remember and the speed occasionally goes very high and then back down again.
Bad connections on encoder feed?
Should actual RPMs appear on the Mach3 control panel?
How tight should drive belt be? It is a ribbed belt, and I didn't go crazy on the tightness, but maybe it should be looser?

These 120v spindle drive boards are no longer available.
Are there any good ways to replace the spindle control board, while still using the 5 axis board and axis drivers?
Any reasonable options to replace 1100w spindle motor?

Thank you,
Bryan