Denford Software & Machines

The Sprint board is removed from the box and I have wired it to mains (pins 12,13), a 10K pot (pins 1,2,3), a wire to start the board (pins 4,5). The tachometer is removed and the board switch set to select the armature voltage sensing rather than the tachometer (S4 on).
The motor runs - but much slower than expected. The armature voltage it is 37V DC, half of what I would have thought for the maximum speed selection on the pot, over 6V on the i/p (pin 3 of the SPRINT board).
If the tachometer switch on the board is off and relying on armature feedback, the motor runs slower than expected from the spindle speed set in VR milling. Re-connecting the tachometer wires and switching the SPRINT switch to Tachometer makes it run at correct speed.

Have now replaced the board in the controller box - and after searching for and replacing fuse F1 which had indeed blown. The motor now runs but pulsed rather than continuous and I hear a clicking sound like one of the relays (or something else) is clicking in and out. Puzzled...and

The old board works fine!
Should've listened to you guys in the first place !!!
After I found where the faulty fuse was located it seemed to fix the problem. In addition the new card appears to be faulty - which also compounded my problem. The new SPRINT card and the old one both worked on the bench with the motor connected - but when in the Mill, only the old one worked. The new one exhibiting a clicking sound and switched the motor on and off.

As I said above, I should have listened to you rather than rushing out and thinking the worst. Goes to show how robust TRIAC PC hardware is.

The advice you gave was excellent - many thanks once again for your brilliant support.

Thats great that you are up & running.

The new card may not be faulty. It may be the Guardmaster switch (Door lock) if fitted. It will come on & off if the motor is run at low speed.
Check the settings of the four switches & the pots against the original.