Ref 54 & 55…
They run from Sprint drive to the drive rack, above the USB board

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Spent a short amount of time, doing some more investigation…
When booting up mill and spindle ramps up, SGR is NOT energised.
With SGR removed, spindle still goes rogue and ramps up on its own!
Removed #54 & #55 from green bar at lower end…
With spindle stopped, 180mV across terminals.
176mV @ 1000rpm
182mV @ 2000rpm
185mV @ 3000rpm
185mV @ 4000rpm

Haven’t got a 10k pot yet for other tests, but will do so soon.

There is an intervening Baldor board.
I’m waiting for Sprint to come back with some more info/prices…
I happy to go with either the 1200 or 1220i… they aren’t ‘megabucks’, but if it’s the Baldor board, it could still be a waste of cash… so still trying to prove what’s what.