Power up the machine and leave it on for at least 10 - 15 minutes to see if the vectors start doing funny stuff like wiggling, fading out, acting funky, etc.
I bought an Asteroids Deluxe cocktail that worked fine when we powered it up at the sellers house... got it home, don't work no more...

... Blew out the dust and moved it back into the house... worked for a minute, then the screen faded out...

sinking feeling too, considering how much I paid for the thing...
I have been able to revive it a few times by doing various things... but it still fades out eventually...

Right now it is in the corner of my shop with a blanket over it... I do not want to mess with it right now, got lots of other projects to play with...
Still, with machines that old, you are pretty much gambling... as soon as you move it, strange things may begin to happen like it did with my Asteroids Deluxe cocktail... It is up to you if you think you will want to mess with it if something does go wrong...
But heck, if the price is right... go for it, even if you may have to invest some time and money to get it 100%...
Like a famous auctioneer once said:
"Ain't nothing in the world wrong with it that money can't fix..." 