Normally on a non-Japanese Sega Master System modded with an FM board, Wonder Boy III is one of those few games that has FM audio but won't work due to the FM audio code not being totally compatible with the I/O chip used in non-Japanese consoles. Thanks to this thread on SMS Power, I was able to fix this issue so I can now play WB III with FM sound on an American console! I successfully tested this patch using a Master Everdrive and it should work with the original cart and an appropriate EPROM.
A link to my IPS patch is included in the link, enjoy!
Wonder Boy III FM audio on an American/European SMS
Wonder Boy III FM audio on an American/European SMS
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