VFD interference problem

[JAZZCNC]

Yes, that's right, but there are two terminals made to replace the USB port, and I'm currently using them:

This could be your problem. The BOB is tying PC ground thru the PP cable to GNd on the 5V supply. For test remove the 5V and power bob using USB.

Regards Spare cheap BOB's that's like simple adding 2+2=4.???. . . Crap + Crap = Crap so why bother.!