Nearly all Macs up until the Beige G3 had a video out port that has two rows of pins, and is slightly wider than VGA - Apple monitors of the time have that connector, or you can get adapters to use normal VGA monitors with them. You can get a user manual (what would have come with it originally) here and a take-apart manual here.
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Your Performa uses a standard Apple D15 video connector. Adapters that allow you to use a generic PC VGA monitor are relatively cheap. In the UK, the second hand price should be around £6 including postage.
does that VGA adapter have dip switches, if it does and they are set wrong you will run into that problem. some of these vga adapters dont come with a manual to show you what to switch on or off to get a certain refresh rate.
the one i have for my Performa 475 is a dip switchless one that works automatically with the monitor you have connected to it.
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Have you checked the PRAM battery? There's no video on that machine if the PRAM batt is dead.
You'll need to get an adaptor. The Quadra 630 supports only 640x480, 800x600, and 832x624 video modes and does not support the portrait monitor.
This I find strange, since its predecessor, the Quadra 605 supported video resolution from 512x384 all the way up to 1152x870, plus the portrait display at 256grays on 1MB of VRAM. (Stock was 512MB but it was upgradeable to 1MB).