I never had this problem with any of my RGBtoHDMI boards. The defaults for NTSC (which I have) and testing under PAL always produced an image. The first three I bought from different sellers all suffered from "sparkling" on some transitions of colors and made them unusable and none of the supposed fixes ever made a difference. (These were the original small boards.) I eventually got two of the LinuxJedi CPLD based boards and both are flawless.
I would check to make sure all the pins are making good contact with the socket, Denise, and the Rpi. It almost looks like when the width or the height are too high in the geometry menu but not exactly. (Two images displayed on screen.) And if these are the default profiles that shouldn't be the case.
