[Mazda Man]

Evening all, I'm looking for some inspiration to solve a hum bar problem on what is usually a simple Bush tv53 chassis. Having done some work replacing the usual waxies and both the smoothing caps as they would not 're form I was pleased with the results. However when I plugged the set in to raw mains rather than the bench isolation transformer there wad a faint hum bar traversing up the screen. When the bar had nearly reached the top another bar started to appear at the bottom. Sometimes the bar traverses back down the screen and sometimes it just hovers part way up. The verticals are not affected in any way as it moves up the screen and no undue hum on the audio. It's best described as a ghostly hum bar rather than a dark black one. Once 're connected to the isolation TX the effect is all but gone. I've not seen this problem before so I'm hoping someone can provide some inspiration as to what is going on as I can't think of a logical explanation but it's very annoying when watching the set.
Thanks