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Jun 1, 2024
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Buenos Aires, Argentina
Hi all,
I've recently purchased a Sega Astro City with bad convergence and geometry issues. While I was able to sort the geometry, the convergence is terrible, to the point where even after inserting small metal plates in the back of the tube (convergence strips I guess these are called?) the issue is still very very evident. I'm thinking on moving the yoke with the hopes of getting some progress, but before doing that I decided it's best to ask in here first. So, I welcome any kind of advice.


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You need to adjust the rings. Do it with the monitor outside of the cabinet. Plenty of write up on this. Not a fun task but you can get it looking great again with a little effort.
Thanks for the quick reply, I did play with the rings, and when I could get something better on that area, the center got broken, so I decided to first make the pixels in the center of the screen look decent enough and then work my way through the corner convergence , but no luck here. Anyway , does that mean that I have to get back and play more with the rings?
Yup. Adjusting the convergence rings will fix this. The second and third rings (If you look from the neckboard up to the yoke) will adjust blue and red so they converge with green.
Thanks a lot, at some point the blue on that corner turned into magenta, and I've got scared, is that part of the process?
The first set of rings closest to the tube will set the purity for each of the primary colors. You need to get this correct before moving onto the remaining 2 sets of rings.

There will be some trial and error here, but as you move them, you will start to see how they interact (splitting the set of rings apart and turning them as a pair) with the last set of rings towards the neck.

You want to focus on getting the convergence good enough in the center 60% of the screen. You will worry about rhe corners later as those can be fixed with the strips or magnets of the correct shape attached to the outside of the tube itself if you want to get things even tighter.
Hey guys, thanks a lot for many responses! About the magnet on the yoke.. how can I tell if I missing one as nem suggested? I'm saying this because the convergence looks good on the middle of the screen already.
Found this picture of a MS9 yoke. Ignore the blue arrow, but I marked some of the magnets in red. If you are missing some magnets in the corner with convergence issues, you may have found your problem.
Hi guys, I was able to take a couple of pictures of the yoke, and all the magnets seem to be in place. What do you think?


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Looks like they're all there. It was worth checking.

I would probably remove the yoke and clean it and the tube underneath. There could be dust or debris that affects the magnetic field.
Most yokes seem to have strips inside them taped down where the copper meets the neck. Are these missing? Might be worth looking around the chassis itself and the bottom of the cabinet. I've found a couple strips and some magnets this way.

As Nem noticed (and I initially missed), one half of the screen looks fine while the other is out. This makes me thing the entire yoke may have been shifted right/left and is causing the issue.
Yeah, I'm guessing the yoke is tilted sideways, and I was reluctanct to move it, because it's glued, but seems like I'll have to try to remove the glue and move a bit. Thanks a lot guys, I'll be posting a couple more entries in the forum because this tube has a few issues, like some 'interference' on the green channel and the horizontal width doesn't reach the full size of the tube.
I wouldn't touch anything yet. Please allow the others to respond first in case I am missing anything.