...ha, the Polo doesn't need an isolation transformer and it runs on 230VAC. However, when we had installed it there was no picture at all. We could hear the crackling of the HV so that was fine. First checked if the signal connector was compatible, which it was so that couldn't be the problem.
So, what steps do you take if you have no picture ?
1) Check HV (was good, we could hear it
2) check neck for neckglow
So...I removed the dust of the neck a bit with a whet finger to see if I could see some glow......but as soon as I did this I found out what the problem was....the neckboard was loose from the tube.....DUHHHH !!!

And so, the Joust is ready for Eurocade. Not yet restored of course, but it works...