Hi There,
I used to have a pixel plus with black bars as well. This is a well known problem on the sets. I eventually got a refund for mine.
The bars sound similar, only appear on dark scenes, about 2/3" thick at either side of the screen. Very annoying once you have noticed them, you never stop looking for them.
I'm not sure, but I don't think a solution was ever found. There was a very long thread a while ago on these forums about the dark bars.
I had an engineer apply an apparent fix, but this didn't work, then they changed the tube and still no joy.
I then got a replacement which had a panasonic tube as opposed to the philips in the previous set. This too had the dark bars but not quite as bad as the one with the philips tube.
If you put 'philips dark bars' in the search bar, the first thread that comes up, should be of interest to you.
Hope this of some help, and good luck.
Regards
Paulj