This is a rally X that wasn't booting at all. After fixing problems with the eproms and the connectors between the PCBs I got it running but with the above graphics issue.
I started looking at the chips after the graphics eprom at 8E but they seemed to be OK. All address and data lines were active so I then tried working back and found a bad output on pin 6 of the LS86 at 7D.
Replacing the chip resolved the issue.
Board now works 100%.