Horizontal Lines at Top of Robotron Screen

Im not talking about the yoke, but the rings. the yoke is just part of the process. you could likely move the whole image up using the rings not the yoke.

Yes. I get it. I adjusted the rings after repositioning the yoke. I repositioned the image and worked on convergence; couldn't get consistent convergence, so put the yoke back where it was originally. The way it's positioned, you have to adjust the rings to move the image as high as you can get it, then adjust the chassis to position the image in the up position. It's still a little low, and the lines appear.

I'm not really worried about it. It will be a while before I pull it out to try again. I've got other cabinets needing work.
 
I wasn't. I was trying to adjust the image position. The vertical size/position was up so high it was rolling over, causing the lines (so the theory goes) By adjusting the yoke, I was able to reposition the image so I didn't have to adjust the image size/position on the chassis as high as it would go. It removed the lines, but I couldn't get the convergence satisfactory.

Like I said, no big deal.

to my point, the vertical adjustments are done with pots on a 4900, or maybe that still used posts, but I could be mixing that up with the 4600 or G07. if you have foldover that means the monitor needs to be capped. playing with the yoke and convergence isn't going to fix that, it's in the actual circuitry of the deflection board.

to my previous point, the lines are normal, you shouldn't feel embarrassed about it. that's just how the hardware was designed.
 
to my point, the vertical adjustments are done with pots on a 4900, or maybe that still used posts, but I could be mixing that up with the 4600 or G07. if you have foldover that means the monitor needs to be capped. playing with the yoke and convergence isn't going to fix that, it's in the actual circuitry of the deflection board.

to my previous point, the lines are normal, you shouldn't feel embarrassed about it. that's just how the hardware was designed.

Oh lord...

Size uses a pot. Positioning uses three pins (U/C/D). Again, I was adjusting the yoke because the wedges were on the bottom of the cabinet, and it positioned all the way down against the neck. I was able to improve the position and get rid of the lines, but messed up the convergence in the process. In the end, I put it back like it was.

I'm not embarrassed. I was just taking a stab at fixing something that is probably too much trouble to fix, if it is even fixable.
 
and it would seem that my comment about there being different yokes for different 4900's seems to have gone unnoticed.

:)

This EXACT thing will happen if you use the wrong yoke with the wrong chassis. I think the chassis that uses a pot wont work right on the yoke thats meant to be used with the chassis with the posts.

Some games dont draw anything off screen like that which is why you dont see it.

Try the different chassis, if you have one.

Also, my comment about c311 in the tapper.....
 
and it would seem that my comment about there being different yokes for different 4900's seems to have gone unnoticed.

:)

This EXACT thing will happen if you use the wrong yoke with the wrong chassis. I think the chassis that uses a pot wont work right on the yoke thats meant to be used with the chassis with the posts.

Some games dont draw anything off screen like that which is why you dont see it.

Try the different chassis, if you have one.

Also, my comment about c311 in the tapper.....

No, didn't catch that. Sorry. IF I ever open it up again, I'll try that. I have a couple of working K4900 chassis. I think they're all the same, though.
 
Just a quick resurrection to add emphasis to what gamefixer said and summarize for someone searching threads.

If you have a game with un-correctable foldover, and it has a K4900 monitor, chances are that the early/later versions of the chassis and yoke got mixed up. It's in a Wells-Gardner tech memo.
https://docs.google.com/viewer?a=v&...FpbnxtdHBhY2lmaWNvfGd4OjM4NzYxZGQzMTNjYTg5NjY
During the life of that monitor a chassis got sent out for repair, or another one got swapped in, and now the chassis and yoke are mismatched.

So, until you have verified that the yoke part # is appropriate for the chassis, it wouldn't be wise to go modifying cap values and such.

Had this problem about 4-5 times with pickups, so I suspect that a lot of chassis got shuffled in the early days. I think it originally was a Ken Layton post that pointed me in the right direction.
https://forums.arcade-museum.com/archive/index.php/t-112474.html

and it would seem that my comment about there being different yokes for different 4900's seems to have gone unnoticed.

:)

This EXACT thing will happen if you use the wrong yoke with the wrong chassis. I think the chassis that uses a pot wont work right on the yoke thats meant to be used with the chassis with the posts.

Some games dont draw anything off screen like that which is why you dont see it.

Try the different chassis, if you have one.

Also, my comment about c311 in the tapper.....
 
Just a quick resurrection to add emphasis to what gamefixer said and summarize for someone searching threads.

If you have a game with un-correctable foldover, and it has a K4900 monitor, chances are that the early/later versions of the chassis and yoke got mixed up. It's in a Wells-Gardner tech memo.
https://docs.google.com/viewer?a=v&...FpbnxtdHBhY2lmaWNvfGd4OjM4NzYxZGQzMTNjYTg5NjY
During the life of that monitor a chassis got sent out for repair, or another one got swapped in, and now the chassis and yoke are mismatched.

So, until you have verified that the yoke part # is appropriate for the chassis, it wouldn't be wise to go modifying cap values and such.

Had this problem about 4-5 times with pickups, so I suspect that a lot of chassis got shuffled in the early days. I think it originally was a Ken Layton post that pointed me in the right direction.
https://forums.arcade-museum.com/archive/index.php/t-112474.html

Very good information. I hope I can remember to refer back to this the next time I pull out my Robotron!!!

Thank you!
 
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