I never had a Bubble Bobble PCB in my collection so recently I bought this bootleg board (original one is too expensive for my taste) called Super Bobble Bobble :
When I powered it up, at first glance it seemed to play fine except for the lack of sound which I promptly fixed reseating and cleaning the sound CPU ROM.But playing some games I noticed that screen was yellowish :
Shorting some data/address lines of various RAM I could identify the ones related to palette circuitry, two TMM2015 (6116 compatible)
Probing the lower one with a logic analyzer revealed that some address lines were stuck low:
This lead me to remove and testing the chip out of circuit where it failed:
With a good RAM chip correct colors were restored:
End of job.