Thank you for the quick response Aaronchan, Some guy and Paul
As Paul asked, yes a banding line is shown when printing solid colours as attached screen shot.
When I print a general artwork, the banding is not shown instead, the entire colour is different.
For example, the brilliant red tone on the screen would be changed to pale red.
I think this is because the yellow ink is not applied properly.
Actually I posted the issue with a mind to clutch at any straws.
I am not sure if I have to buy a new small one (7900) or call the tech of Epson.
Thanks anyway.
Hee