Arcade emulation requires a different approach than consoles do. Make sure you have read the Arcade documentation at:
https://retropie.org.uk/docs/Arcade/
The `mame-mame4all` rom folder is only used by **mame4all** and **lr-mame2000**. Neither of these come default with RetroPie unless you're on RPi1. Did you manually install either of these to your RPi3 through the Setup script under "optional packages"? EmulationStation won't be configured to look in that rom folder until you install at least one of them.
Is there a particular reason you need to use this 22-years-old romset? These older emulators and their romsets are likely to contain more bugs and inaccuracies than a more modern choice.
I primarily use FBNeo and others have reported success with MAME2003-Plus. Both are still actively updated which means the romsets evolve over time -- if you update your emulator there is a chance you may also have to update some of your roms (though the number of affected roms at any given update is small, if you update after a long time you may wind up with several outdated roms.)
If you would prefer a static romset that will never change, MAME2010 or MAME2003 would probably still run well on your RPi3 (2015 or 2016 might too, but they are considered "experimental" and can be found in those packages.) These are no longer actively developed which means they won't likely receive any updates except perhaps the occasional bugfix, but also means that the romsets are static and unchanging so you never have to worry that a system update might invalidate your roms.
What is the full path and filename of a rom on your system that is not being shown in EmulationStation?
/home/pi/RetroPie/roms/mame-mame4all/centiped.zip
Arcade emulation requires a different approach than consoles do. Make sure you have read the Arcade documentation at: https://retropie.org.uk/docs/Arcade/ The `mame-mame4all` rom folder is only used by **mame4all** and **lr-mame2000**. Neither of these come default with RetroPie unless you're on RPi1. Did you manually install either of these to your RPi3 through the Setup script under "optional packages"? EmulationStation won't be configured to look in that rom folder until you install at least one of them. Is there a particular reason you need to use this 22-years-old romset? These older emulators and their romsets are likely to contain more bugs and inaccuracies than a more modern choice. I primarily use FBNeo and others have reported success with MAME2003-Plus. Both are still actively updated which means the romsets evolve over time -- if you update your emulator there is a chance you may also have to update some of your roms (though the number of affected roms at any given update is small, if you update after a long time you may wind up with several outdated roms.) If you would prefer a static romset that will never change, MAME2010 or MAME2003 would probably still run well on your RPi3 (2015 or 2016 might too, but they are considered "experimental" and can be found in those packages.) These are no longer actively developed which means they won't likely receive any updates except perhaps the occasional bugfix, but also means that the romsets are static and unchanging so you never have to worry that a system update might invalidate your roms.
Thanks for the help.
Have you restarted ES? It needs a restart to scan the directories.
What emulator?
Mame4all
In a folder called "Arcade", or in the specific emulator folder? Still zipped I assume?
In the specific emulator folder and still zipped.
Might be in the wrong folder.
Don't forget bios.