Nice looking machine. You're welcome for the reference page I sent. Actually, Jim sent me a PDF file with information on the Bally machines. Covers the machines from 742 to the 1090s. It's a good cross reference to help ID a machine if the Bally tag is missing. What I like the most is the model number suffix that Identifies the casino the machine was shipped to. Out of the blue a machine came up Labor Day weekend, bought it on my mothers birthday. Come to find out the machine was built for the Fremont casino downtown Las Vegas.
This is one of the casinos where my parents would gamble. There is a good chance they dropped a few quarters into the machine.
Anyway, one of the first things that would help the machine is a good cleaning of the contacts and moving parts that are covered with old lubricant. While cleaning, inspect for broken wires, missing coil springs, contacts not opening or closing and anything that looks overheated. Just about every moving part can be manually manipulate and reset for testing and functionality.
I usually start where I think the problem may be. Or the hopper if the machine is operating.
Recommend doing cleaning a little bit at a time. Then test machine to see if there is a difference. Cleaning a multitude of switches at the same time highly increase the odds of not finding the actual problem and or causing more problems, believe me I think we have all been there a few times.
Good luck on your machine and have comfort knowing you have a lot of knowledgeable persons on this site to help you out.
PS, for cleaning I like denatured alcohol and Q-tips for the contacts and PB blaster for the moving parts.
I'm sure there will be other recommendations and if you come across some really good cleaner lets us know.
And always test your cleaners before using the first time.