I am using a Harbor Freight mini mill which has the FC350BJ spindle controller. I have converted this machine into a complete CNC (including the spindle). This setup has worked perfectly for some months now. However, when I went to build a second machine, I started getting problems with my spindle. To further explain, when the spindle is running it pulses on/off as if the door switch pins (6 and 7) are opening and closing. In fact, I can hear the on/off clicking from the controller. This problem usually happens at speeds above 1000rpm. Has anyone ever had this problem? I've checked my connections and they all seem solid, but the problem continues.

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