That is nothing to do with the firmware. You need to load the parameters for your machine....
You can also boot it into the Parameter editing mode and manually adjust parameters as well. If I remember right the machine width one is meca size and there are a few valid values like 0, 1, 2, or 3 which are the various machine widths.
Ideally though you need a backup of the parameters from your original mainboard as they are somewhat specific to each individual machine. Even with the correct size entered things might not work right....
I cannot really be of more help though - JV3 is an ancient machine and we have not had one in probably over 10 years now (upgraded to a JV33, then a few years ago upgraded again to a JV150).
