A friend got a Mahou Daisakusen (japanese version of Sorcer Striker) board with faulty graphics.
It was playing fine with sound but there was an obvious color palette problem.
I started looking at signals around the color outputs of the PCB and quickly found weak signals on the 74HCT273 at location U12. Piggybacking the chip with a working 74LS273 fixed the colors immediately.
I replaced the chip… Board fixed.
Here is a picture of the PCB with the defective chip highlighted in red: