Your problem may well be a magnetised bolt.

What happens is like this: The machine is installed in it's original home (presumably an arcade) and left there for a long time. Turned on and off for years, the degauss coil, or even just normal current flow in the deflection yoke, will slowly allow the steel fixtures in the machine to become magnetised, usually in line with the geomagnetic field at that particular location and orientation. It essentially 'sets' a local magnetic field which aligns with the geomagnetic field. This normally doesn't show any ill effects as everything is lined up correctly as long as the thing is left where it is. If you physically change the orientation or location of the machine, THEN you get all sorts of pretty results as the field lines now don't line up properly.

This will effect any crt based system, but normally things which are designed to be moved around such as oscilloscopes are both shielded correctly and have compensation controls to allow you to adjust this sort of effect. Scopes, in particular, show it as a tilt of the trace from horizontal, since it tries to line up with the local inclination of the geomagnetic field.

TVs and similar colour CRT based equipment are much more sensitive to magnetic effects, as you can immediately see even a small field change as colour fringing. A good demo of this is to turn on a TV or monitor, wait for the degausser to finish doing it's stuff (about 15 seconds) then turn the thing through 90 degrees onto it's side. Trippy The risk is eventual long-term and very difficult to remove magnetisation of the shadow mask. The degauss coil will normally remove this local field, or actually realign it, when the thing is moved. In your case, I would imagine that your degauss coil isn't working at all. The local field causing the problem is probably coming from the CRT corner mounting bolt. You either need to get the internal degauss circuit working, or use an external degausser on the tube.

pca