Non working games can be a blessing or a curse depends on who is selling them.
Buying non working games from a highly technical person means normally it not going to be an easy fix.
Buying a game from a non technical person gives you a better chance getting the game to work.
Some games have batteries that cause corrosion on the mother board. They are much harder to work on.
Some games are not repairable due to the damage that occurred when they died. Lighting strikes come to mind. High voltage to the pcb come to mind.
Some games are rare enough and valuable enough to spend enough time on them to repair them. Some are just not.
http://www.arcade-classics.com/exidy_arcade_price_guide.html
Is a rough guide on the value on these machine. Condition is important so is the serial number. A low serial game can be worth more. Do a complete auction check on ebay to see some of the values..
If you do want to learn how to fix these games, have some basic electronic skills is important o have. See if you can find someone local to give you hand.
Do not go into repairing thinking your going to save money. Sometime it cost you way too much in time to repair an item. You will end up working of less than minimum wage.
If you just want to learn you will need Dvm, logic probe, esr meter and a scope will all help you in repairing arcade machine.
Oh yea an a soldering iron to remove and replace parts..
I hope this helps..