I'm the one who told him about yoke tabs. Because in this case that's what's needed.
Either that, or the yoke itself isn't straight. But most b/w vector's (and Asteroids Deluxe in this case) don't have centering adjustments via pots. If the image isn't centered, the yoke must be adjusted.
@spisi, with the monitor off, check to make sure the yoke hasn't loosened up. If there's play, you can loosen it via the screw clamp on the yoke (which holds it to the neck), adjust the yoke back closer to the center, then tighten it back up.
Beyond that, there are two metal tabs on the back of the yoke. They can be rotated around, which will change the centering of the image. However this adjustment will only move it a relatively small amount. In your case I suspect more that the yoke itself has shifted, and isn't centered.
If you're going to try to do any of these adjustments with power on (which is the best way, but also the most dangerous), you want to make sure NOT to touch the anode wire, or any of the yoke wires. You can do it, you just don't want to be wearing any jewelry while you do it, and always be aware of where your hands are. And do it in an environment that is free from distractions, where you can focus 100% on what you're doing.
View attachment 787784