EPROMs are sometimes the scariest things for technicians who haven’t had to deal with them, as buying preprogrammed EPROMs if you can even find them, is quite expensive.
But a simple EPROM programmer like the MCUMall GQ-4×4, which can be had for around $100, will make it so you can easily test, reprogram, and most importantly for rare machines, backup.
If you suspect an EPROM has failed:
Connect your EPROM programmer to a PC with the required software. You will also need a known good version of the ROM which can be acquired through various sources… Most likely it will be in the form of a ZIP file with something like ‘MAME’ in the title…
Unlike how you’d use it in an emulator, you need to unzip the file and inside that you should see files with names that should line up with specific chip locations on the PCB.
Now, simply load the file that corresponds to the chip you need to test, select the correct chip in the software for whatever chip you are testing, install the chip, and hit “Verify”, it will compare the known good file with what it can read on the chip.
If it verifies, that means the chip is good!
If it fails, it doesn’t 100% mean it’s bad. Some chips won’t verify even if they are good, but that is uncommon.
Verify you had everything setup correctly. You can also “read” the chip, save it to a file, and then use an online arcade ROM verifier to see if the dumped ROM matches anything in case there is something wrong with the ROM you verified against.
If all that fails you have two options.
If it’s a PROM, you will most likely have to replace the chip with a compatible EPROM. If it’s an EPROM, you can attempt to wipe it if it’s UV Erasable. If the sticker is missing from the UV window, it might already be erased. If not, remove the sticker and use a UV eraser to wipe the chip.
Then simply select the chip in the programmer options, install the chip, load the file, and hit “Program”. It should go through programming it, and then it should verify it. And there you have it, a freshly programmed EPROM. Now just put a sticker, label, or tape over the UV window, and it’s ready to use.
To backup a EPROM:
Simply select the chip in the programmer’s software, install the chip, and hit “Read”. Then, once that finishes, simply save that file with a name that will help you identify it, such as the game/board name, the chip location, software version, and what kind of PROM/EPROM chip it was. And just like that, you have a backup.
Now you can simply take those files and put them on Archive.org with all that information, and you will not only help anyone else in need of that file, but you may end up helping yourself if you end up losing your personal backup of it.