Re: TV keeps losing its convergence calibration..
Well there are only a couple of things I can think of:
a) you live somewhere where the earth's magnetic field changes quite a lot from day-to-day. Its quite improbable but certainly not impossible.
b) you have speakers and other equipment in your room that produce a magnetic field and the variation in their magnetic field is causing convergence to screw up.
c) your tv is defective (probably most likely).