Got this Irem X-Multiply PCB (actually a conversion from an Hammerin’ Harry M81 board) from my friend Josef for a repair:
It showed a graphical issue where some sprites (like enemy shots) were blocky during gameplay and backgrounds missing during attract mode:
Sprites and tiles data are stored respectively in eight 1Mbit EPROMs on video board for a total of sixteen devices.
Original devices were 1Mbit 28 pin MASK ROM:
while who made this conversion used ST M27C1000 :
Video board has some jumpers which must be closed according to the type of adopted devices :
In this case the jumper configuration was set to ‘EP’ so not suitable for 27C1000 but required the use of JEDEC devices like 27C1001 or 27C010 (while the ‘MASK’ setting can work straight only with the original 28 pin 1Mbit MASK ROMs and not with 27C1000 which, although the similar pinout, have some extra pins to deal with, so some modifications are needed)
Reprogramming all the data for sprites and tiles into 27C010 1Mbit JEDEC EPROMs fixed graphics completely.