MMC6 having no sound output? - EDIT fixed it

This is an archive of a topic from NESdev BBS, taken in mid-October 2019 before a server upgrade.
View original topic
MMC6 having no sound output? - EDIT fixed it
by getafixx on 2019-09-29 (#242864)
I'm working on incorporating MMC6 support into my MMC3 mapper, and I've got the Star Tropics games working in that I can create and save and play the game just fine, but I have absolutely no sound output. I've tried on a clone and a couple of other consoles so far...and I can't figure out what it could be other than the PRG RAM protect register not working properly? MMC3 games work just fine and with sound.

According to the wiki MMC6 is just an MMC3 with extra registers for RAM protect, but is there anything else I could be missing?

EDIT: Nevermind, just found this on the wiki:
Code:
Because write protection is generally only used to guard against corruption during power off, many implementations of iNES Mapper 004 simply omit the write protection. Leaving PRG-RAM always write-enabled removes most of the incompatibility between MMC3 and MMC6, and is sufficient to support the popular MMC6 games StarTropics and StarTropics II.


Removed the MMC3 ram protection bit and it fixed the no audio output. Just had to re-read the wiki a again!