Are you getting barrel distortion?

Barrel distortion can occur (and most likely will) if you are trying to stretch the screen horizontally and vertically to erase the black bars that are seen after the upgrade. I added a ceramic capacitor to position CL 26 and that corrected the problem.

To remedy (courtesy of Stuart Bell's World Of The Power Color Classic) please follow the instructions below.

One common problem is that, even after much tweaking of the controls, the final screen has wide black borders at either side. The bekkoame site offers one solution, which is to increase certain voltages on the analogue board. An alternative is to add a capacitor (1 to 4nF) rated at 1500V+ at position CL26, adjacent to the flyback transformer. This worked well for me. Thanks to Joerg Garritzmann who first proposed this idea.

Here's a little more detail about the modification:

The ideal is to do the standard conversion, then adjust the display to get the widest display before it becomes impossible to get nice straight sides (barrel distortion sets in!). Then add 1nF/1000pF, and adjust again to optimise. If it's not wide enough, add a bit more capacitance and repeat. Joerg found no improvment beyond about 3nF; I found that 4nF was optimal. Because the effect of the mod. is to 'spread out' the TV signal over a longer period for each line, maximum brightness is reduced, but not by a large amount. This method doesn't put extra strain on components by increasing key voltages, which the alternative method on the "640 x 480" site does. So, ideally, you need to source several caps in that range. Incidentally, this fine tuning, including removing the analogue board each time, takes far longer than the actual modification to get 640 x 480 in the first place. But it's well worth it. You need every inch of display available at that resolution. And just to clarify WHERE position CL 26 is, here's a photo showing a 4nF capacitor in place next to the flyback transformer:

Picture of CL26 Picture of CL26