Looking for some advice on where to focus with troubleshooting a System 3 display driver board. I got this board non-working and missing a U8 chip. I bought a new U8 from PBR and installed it. Upon plugging it in I checked all of the voltages and they are in spec. However there are artefacts all over the display with blank (black) sections regularly spaced apart. You can actually see what should be on the display in the lit sections but it is hard to make out. The animations move and progress normally. I have replaced U4 with no change in behaviour. This board was tested in a working game so ribbon cables and other hardware are not at fault. I suspect one of the other ROMs is at fault but not sure which one it could be.
Can anyone advise before I start shotgunning them all? noflip95?