Some things I've noticed with mine that have absolutely nothing to do with your symptoms. 1. throw a mounted tire on it, spin it, get weights to add. spin it again, still asking for same amount. 2. add weights, spin it, wants more, ask it again, still wants the same. 3. add weight the 2nd time, spin it as often as I want and it comes up 0. 4. rotate the rim 180 on the head, spin it, it wants more weight. Usually about .25 or less and book says this move could give a reading of up to .50 diff. If it keeps telling you to add weight in a different location kinda tells me it noticed the last one go on - just not how much / where? The amount it's asking for being just about the calibration weight makes me really suspicious. The whole measurement head is one assembly, maybe it's loose and wondering around? Long shot: random stray dirt mark on the exposed strobe wheel? like 3 screws to take the tray off and look.