Jim,
I was going to split the encoder signals to the original, and the 7I77 board, then leave the original box alone until I made sure the feedback from the scales was good in LinuxCNC. kind of saves the fooling around with a travel indicator, as you have a running system to check to. This would also allow checking voltages under motion while the original box was set up. Mine is early enough that it has the reset for the drives on the side of the box for the drivers and power. As for the main cable, I disconnected it and the control fires up and the DRO reads position and feed velocity. Seems like overkill, but they are actually pretty cheap, and with a 9 volt battery, an LM7805 regulator chip and some alligator clips, you have a standalone encoder tester. If you are going to build more than one machine, they could be good toolbox pieces. The goal is to remove the original controller, make a new smaller box and use the little Dell Optiplex 755 I have for the control. I would like to build something like ALLOY CRAFT did for his CHNC Hardinge, check out the link here, he made a really clean setup.
forum.linuxcnc.org/forum/30-cnc-machines...-way?start=110#44388
