Just got done repairing a Tempest Cocktail and an Upright for a guy (guess he like Tempest).
Just remember that the color X/Y monitors had a problem handling the attract "Tempest" screen and had a tendency to lose the picture quite often. The monitor has to work harder to get the picture spread across the entire screen, especially the graphic-intensive title "movie". I've seen some Tempests last 10 years with no problems, and others lose their monitor every 3-4 months or so.
The problem usually comes in the low voltage portion of the monitor chassis. There is now a fix that is supposed to make the monitor "bulletproof". It's called LV2000 and replaces certain parts on the low voltage board. You actually have to strip off about 12 parts or so and solder in this mini board, so some skills are required, but the whole thing costs less than $50, I think. (Just checked - $36)
Here's a link:
http://www.geocities.com/jeffhendrix67/lv2000/We install this in every Tempest we do (if we can get the customer to pay the extra $36 for it) and haven't had a monitor go down that has had the upgrade added (although time will tell.) The best part about this little board is that it has pots on it for fine-tuning the +26V and -26V for the low voltage board if you need to, although they're usually set when they arrive. We don't put them in Star Wars, Space Duel, etc. unless the customer wants it or the game has a recurring problem.
The guy (Jeff Hendrix) actually has the schematics posted on his page, so you could probably even build it yourself if you had tons of time, tons of parts, and no money.
(And just in case you're thinking I'm a spammer trying to direct money to this guy, here's a free fix.)
Of course, even without the upgrade, you can help protect your monitor from being overstressed by the attract mode by adjusting your picture height and width down. No longer needing to fill the entire screen will keep the monitor from working too hard. You'll have to play with a smaller picture, but at least you'll have a picture.
Either way, good luck with your Tempest hunt.