Hello! I'm waiting (a few months from Japan to Brazil) CM-500 serial ZD41184, it looks like an older unit, it only have the GS logo . This mod will work with any version of the CM-500, right?
When it arrives I will give a try in the mod. Just need to figure out how to burn a 27c512 in a NIC. Some fellow people of Vintage Computer Forum done this a few times.

Thank you guys, this will be awesome.

Cloudschatze wrote on 2023-01-10, 03:33:

Separate from the LFO/vibrato issue, I am currently troubleshooting yet another errant CM-500 behavior, this time related to the MIDI switching/handling function of the Mitsubishi 7702 MCU. If anyone happens to have a CM-500 with a serial number greater than ZE13000 (with corresponding "CM-500 1.02" ROM @ IC22), can you please get in touch with me?

Is this something you're still after? Didn't see in this thread if you got what you needed. I have a CM-500, serial ZE14382 with the 1.02 ROM installed, so let me know if I can help. Couldn't send a PM, haven't posted here enough to do that yet apparently.