I have found that when I rotate the picture centring magnets to try to get the picture in the right place it goes blurry. Does anyone know why this is? Is it usual to have to adjust the focus when adjusting these magnets? Problem is the focus pot is all mangled and I cant move it......

Dear Stumaoo.

It does sound a little strange to know that there is a H.M.V. F5 in England.

Never the less, to your problem.

The focus of the tube should not change with the rotation of the picture centring magnets.
The picture tube in that model has electrostatic focus, which usually has very little noticeable effect on the picture, but you may have given us a clue. You say that the focus control does not move/faulty. The focus grid within the tube might be floating (not connected to anything) causing the poor focus. Why this would change with the rotation of the centring magnets, I don't know
.
According to the service manual for this model, the voltage at the focus pin of the tube should be between 230 V to 510 V This focus voltage is modulated by T9 to give a voltage that varies from the left side of the tube to the middle of the tube to the right side of the tube. This variation will not be measurable with a meter. This model appears to be better than the usual run of the mill TV. Many sets have a flying lead connection to the focus grid, with the choice of one of three options.
1. 0 V
2. B +
3. A voltage somewhere between 300 to 500 volts.

I hope that this has been of some help to you.

Wayne.

I have a similar focus vs centring problem with my 79-2/3 Kriesler. See post in this forum.

Yes the F5, working properly, is a very good performer.

Might be you also have a replacement CRT with a short neck. Does your F5 have the metal shield around the yoke? If so, you may be able to remove it to allow the centring magnets to be moved up against the yoke. The rim band by itself should be able to support the tube without the 4 metal straps if you use suitable cloth or neoprene adhesive tape around the bulb.

The F5 used a Rola yoke and the plastic back on it would have probably crumbled away by now. You'll need to come up with a replacement....

Or have you tried degaussing it? You never know, that might be all you need to do.... Assuming you can still find a degaussing wand.....