Gottlieb pinball manuals aren't generally available for download, unfortunately.

However, a new copy can be bought from The Pinball Resource. There's also a copy on eBay here: ebay.com link: Gottlieb Freddy A Nightmare On Elm Street Pinball Machine Manual Schematics NOS

I did a little research on the issue you're having, and the first thing i would check is the +5V DC supply. It appears there is an adjustable trim pot that can be turned to raise or lower the +5 supply to get it just right. Adjusting the pot to correct the +5 volts may only be a temporary fix though, it appears they are better off being replaced entirely. I copied/pasted a bit from a general Gottlieb system 3 repair guide to elaborate:

"Because the Gottlieb System3 power supply has a 500 ohm adjustable trim pot for the +5 volts, it can get out of adjustment. It is best to test for proper +5 volts at the CPU board. Note there are no test points. Use the A1P1 connector (pin1=+5, pin4=ground). The voltage should be 4.95 to 5.15 volts DC. If it is outside of that range, adjust the A2 power supply trim pot. Note this trim pot is notorious for being worn out. Replacing it with a new quality trim pot is often a good idea. If +5 volts varies a lot on a game from time to time, suspect this trim pot as the problem."

Also, welcome to the forum! There's lots of great techs here that may be able to help you figure this out if you need further assistance.

Good luck!!

Good stuff!

Enjoy your game!!!