By swapping the boards with another known working system 11 game, I could determined that the issue lied in the CPU board.
I quickly found a missing signal on a LS08 with my logic probe. Following the trace I saw it was connected to the main CPU.
In fact the board took a shock (poor storage) and around 30 pins were desoldered on the main CPU:
I fixed it using hot air and the game then booted:
Drum roll: it's Kosodate Quiz My Angel 3... Awe... some...
First I already own this game, second it's a quiz game in Japanese where you play a girl from birth to age 25 with the ultimate goal of getting married.