The explanation by viletim on this page, as well as how to fix it on some PCE models :
http://etim.net.au/av-driver/pcebars/
Some useful cap maps for more models on the Console5 wiki :
https://console5.com/wiki/Hu6260#Jailba ... al_Bar_Fix
I'm going to try the fix on my SuperGrafx.
I can see the banding best in Battle Ace, both on my small Trinitron and via the OSSC, just at the start of the first level, when there's a white flash, that then turns into a blue sky.
By the way, the link given by Artemio below is now dead, can someone re-upload it somewhere ?
Artemio wrote:I did make a small rom before making the suite that has the patterns that show banding in my setup: https://dl.dropboxusercontent.com/u/1403041/banding.pce