I'm beginning to get into importing games from Japan and patching them using the Retron5's patching capabilities. Needless to say, the wonderful work on this site has been indispensable in playing translations of games never released outside of Japan. However, sometimes the patches won't work on certain cartridges and I assume that it may be a header issue. From lurking and research, I've found that you can determine whether or not a ROM has a header by the ROM's size, so is it possible to determine the size of a game before I purchase it - i.e. is there an easy way to determine the ROM size from some marking on a chip or something? Or am I just going to have to gamble with buying carts and hope that if it needs a header the ROM has a header and if it requires no header that the ROM doesn't have one?
This can be a problem since you can not manipulate with the cart like you can with the ROM file.
Not only can not see the size, you also can not see the code, unless you scan the cart back into a ROM file again. You thus can not calculate the CRC (checksum id) of your rom. Since the header might not be the only issue.
Usually carts don't have headers by default, since this is a leftover by the copier, but you never know.
It can be another problem, if the patch is made for the headered rom, and you have a cart without a header. You then need to use a PC in any case, to patch to a headered rom file.
You need to get the rom file of your game and patch it correctly (header, region). This is not a problem on a PC, where you have multiple options.
Once the correct rom is patched and the hack works and is tested (on emulators), make another IPS using Lunar IPS by comparing the hack with the original non headered rom. This IPS should then work with your cart.
In any case, if you buy a cart, it doesn't matter if it is headered or not, you can make a working IPS in any case.
You can even make multiple IPS files. For instance create IPS by comparing (using Lunar IPS) a working hack (rom file) with US, EU and J original rom files, all headered and non headered. You will thus get 6 IPS files. Once of them must work with your cart on Retron.
You are also required to do the same if the patch on the site is UPS or Xdelta patch (instead of IPS).