@grand_national you need to show a screenshot.
service menu is entered pressing F2: https://retropie.org.uk/docs/lr-mame2003/#service-menu
mame menu is entered pressing TAB or R2: https://retropie.org.uk/docs/lr-mame2003/#mame-menu
I guessed at the button config for the controller when EM first started and config'd what I thought to be the minimum.
does not inspire confidence... what layout did you use?