To get into service mode all games will begin with pressing and (HOLDING) the F2 key. Using the arrow keys to navigate and usually the ctrl key to make a selection. Inside service mode you will see different options to choose from. Examples: lives, continue, price, level of play, color of charcter. The basics on all games are in the following order.

F2
arrow keys
ctrl key
F2

There are exceptions depending on the game you may have to use the alt key and space bar. The best thing is to do is to experiment with it. You can't screw anything up. If you get lost inside service mode just hit the esc key and delete out the nvram file of the game you were in. Then when you go back into the game it will be just as if you never were there in the first place.

(MIDWAY)

Raising volume level
Mortal kombat ll all revisions
Mortal Kombat 3 (rev 2.0 & 2.1)
down arrow key to select - volume adjustment
ctrl
up/down arrow keys to raise/lower volume
ctrl
down arrow key to exit
ctrl
down arrow key to exit
F2

To exit some games you will need to press F3 instead they are.
mortal kombat 3 (rev 1.0)
utlimate mortal kombat 3 (rev 1.1)
utlimate mortal kombat 3 (rev 1.2)

NBA Maximum Hangtime (rev 1.0)
NBA hangtime (rev L1.1)
Raising volume level
down arrow key to select - volume adjustment
press and hold F2 until you hear a sound, press F2 again
up/down arrow keys to raise/lower volume
ctrl
down arrow key to exit
ctrl

NEO GEO GAMES

Metal Slug, Metal Slug2, Metal SlugX, Metal Slug3
turning the blood on
arrow down key to select - setting up the soft dip
ctrl
arrow down key to select - slot1 metal slug
ctrl
arrow down key to select - blood
ctrl
space
space
arrow down key to select - exit
ctrl

NOTE: To make this save so you do not have to do it each time you play make sure your cfg, nvram files are archive only. If anything else is checked uncheck it.

I think most people that get the basics down will have no problems. However if you do encounter any problems e-mail me and I'll look into it to see if I can help you out. You can find my e-mail at the bottom in the left column.