I have a error #8 in fadal 4020, when I put the command m3s500 de spindle run and stopped, run and stopped several times. after the machine send de error #8, I am traying run the spindle directly from inverter in mode jog but I have the same problem.
I was having a problem like this. I looked and my VFD had no errors, so I put my VFD in manual mode and ran it with no issues at all in manual. So I put it back and remote and the issue returned.
I then check and cleaned the connections tot he spindle 1050-1 card and the little coax looking connectors and the problem never came back.
Also, check the little round reset buttons in both cabinets.
You likely have a problem with your spindle controller card or inverter. When you get alarm #8, this is telling you that your motor is spinning with no movement from the belts, like they are off the pulley. If your belts are good, check the code on your drive. You could have an intermittent fault with your Hall effect as well. You can shoot it to me and we can get this figured out for you.