I have mostly gotten lucky with old machines like that when booting them... but that said here are a few things you ideally should do:
- replace the clock battery; probably a 3.6V 1/2 AA but look it up for the Quadra 630
- open up and inspect the motherboard for any leaking or bloated capacitors
- remove any dust/debris from the fans, motherboard, and power supply (also look at capacitors on the power supply if visible)
- inspect the power cable for any cuts in the rubber (these are usually generic and easily replaceable)
At a minimum I would replace the battery. It's not a real issue until it leaks (it just won't hold the time if it's out of power which it almost certainly is after 25 years of no use) but they are really in trouble of leaking at that age.