Bob,   I built the LVB tracker up from one of Howard's early bare boards.   I had these problems interfacing to an old Wilson 550 rotor. I added relay circuits inside the old rotor box. The relay coils had supression diodes. The relays were switching 120 VAC which I think was the root cause. I started this project with the LVB tracker's power supplied from the rotor. I eventually gave the LVB tracker its own supply. Then I added supression circuirtry inside the LVB Tracker cabinet. I finally solved the problem and ran for years until the rotor just gave out mechanically.   The spikes would stop the tracker in a pass when there was relay activity. Sometimes I could just power down/up and  the LVB tracker everything would be OK. Sometimes reload SATPC32, and occassionally it would corrupt the calibration constants so I had to reload. One thing is certain, the LVB Tracker is a tough one.   When the rotor gave out, I purchased a 5500. No problems using the 5500.   Food for thought, and I don't want to send you down the wrong path.   Listen to Howard.   Good luck with your problem.   Mike K9QHO