Ok so new disc installed and the same outcome no hidden characters unlocked . Anyone know if the disc or the dongle is the key to have all characters unlocked ? I also noticed my game when it shows the attract screen it shows only tekken 5.1 without heichais face in the background of the title screen . I have seen other version have heaichis face with the game logo .
If its a time unlock maybe you could use IDA to dissemble the binary, searching for a real time clock call or comparison (CMP)...
If you manage to find the memory offset of this value, you could then easily edit the jump points so no matter what value was returned by the clock it will always jump to successful outcome/unlock.
Pretty sure someone made a EE (PS2 CPU) profile that can be loaded, no the source won't be very accurate but finding the offsets is the only goal, then hexedit the binary.