Game booted but with a dominant green tint (forgot to take a picture) and was silent.
Concerning the colour issue I probed the colour RAMs (2 of them) and the one @ E4 (U096) had weak data signals. Piggybacking it cleared the issue so I replaced it:
For the sound problem I found the audio RAM @ C5 (U118) was dead too altough piggybacking it didn't make any change. This game uses a weird custom chip noted YM3931 (not sure it's linked with the Yamaha brand) for sound. I was sure of it cause it's connected to the audio RAM, the YM3812 and the OKI M6295. Anyway, many of what I thought were outputs were silent. This also isn't normal, the chip is a SDIP64 (shrink DIP with a pitch of 0.07" instead of 0.1" for standard DIP) and very few legs were active. Luckily my friend Kelvin found the chip somewhere online for $8 IIRC:
I replaced it and sound was brought back to normal.