SO, a few things to try. If your max field pot is too high, it can cause the jitters. The tach shield should be grounded at the controller end only. A bad 3ea board, 2ea board, 1ea board,can also cause it. The 1 and 2 ea boards are inter-changeable, plug and play. you can try swapping them, and see if the problem changes. Also the stabilility pot being too high causes it. These things are a Beast, so one thing at a time. Check the tightness of terminal connections. Good Luck.
