the service menu is only accessible by pressing a button inside the machine. this keeps customers and other idiot people from messing with the settings.
if left to the end user, they would issue 100's of service credits and crank up the volume till the speakers and amp blow. that's just how they are.
source: placed a convenience button outside a machine once. service call 2 days later. wrecked the speakers, amp...and not a buck was to be had in the machine.