I am in luck! the +5V rail from the PSU went crazy and supplied the PCB with more than +7V for 20/30 sec before I managed to switch it off .

At least one chip or component was damaged in the process since there is no more graphics but only vertical lines displaying.
With help from the diagnostic bios, the SM1 was found unresponsive.

Indeed M1 address inputs are set high w/o pulse while data outputs carry no signal at all.

I have replaced the M1 but no improvement so now I am looking towards the NEO-CMC.

Based on the pinout from NeoGeoDev, how is the CMC being enabled?