Robotron Type B Monitor Horizontal Center

camperjohn

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I have a Robotron, and the horizontal center is off. The manual, shows how to adjust using the horizontal center...But my monitor trim tabs don't match up with the photo in the manual.

Looking at photos, which potentiometer do I adjust to center the horizontal?
 

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Horizontal and vertical center are not pots. Just a plug and 3 pins each.
Just use the left plug and move it to the middle pin (monitor off).
 
Try this diagram.
 

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Ok I moved the jumper to the middle tab - it looks worse!

I think I am stuck with the lines on the right side. I will move the jumper back to the original location.

I will also check the positioning of the actual monitor in the cabinet. Maybe it was moved and not mounted in the cabinet correctly and I can push the monitor so the lines are not visible.
 

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I don't remember those lines on Robotron. I don't think they should be there. Perhaps someone can jump in to confirm.

Assuming that your monitor is in good working condition with correct B+ voltage, etc. you can try adjusting the width coil to expand the picture. After that, try the jumper taps again to center the picture.
 
The h-freq pot can move your screen left and right as well. At some point if you turn it too far the screen will get wonky looking and squeal. No biggie, just turn it back a touch.
 
The h-freq pot can move your screen left and right as well. At some point if you turn it too far the screen will get wonky looking and squeal. No biggie, just turn it back a touch.


+1 on doing this.
 
After adjusting the horizontal width coil?

I didn't try to adjust the horizontal width coil. I'm a little afraid at the moment.

Can I do this while the machine is on so I can see the results, or should I unplug it and stand back about 20 feet while doing this?

I am very aware of the high voltages that are associated with CRT's. Even when they are unplugged the capacitors are not very safe to put your tongue on.
 
If you have the properly sized allen wrench or preferably, plastic tool. Turn off the monitor, reach back there carefully, and adjust it counter-clockwise, 8 or 10 turns, then turn it back on and see what your results are.

The width coil in total, only adjusts the width (wider) about 1/4" or so.
 
I didn't try to adjust the horizontal width coil. I'm a little afraid at the moment.

Can I do this while the machine is on so I can see the results, or should I unplug it and stand back about 20 feet while doing this?

I am very aware of the high voltages that are associated with CRT's. Even when they are unplugged the capacitors are not very safe to put your tongue on.

You can definetly do it with the monitor on so you can see the results, I do it all the time. Just make sure to use a non-metallic "Allen wrench" or else you can break the ferrite core. Nothing wrong with making the adjustment with the monitor off though, a little more time consuming but that's it. If you have one of the shorter adjustment tools you can tape something onto it to make the shaft longer, I've used chopsticks and pencils before.lol.
 
You can definetly do it with the monitor on so you can see the results, I do it all the time. Just make sure to use a non-metallic "Allen wrench" or else you can break the ferrite core. Nothing wrong with making the adjustment with the monitor off though, a little more time consuming but that's it. If you have one of the shorter adjustment tools you can tape something onto it to make the shaft longer, I've used chopsticks and pencils before.lol.

I like the idea of a pencil. I will do it with the monitor on and view the results in a mirror.
 
SOLVED: I used a pencil to adjust the horizontal freq and that did the trick. I no longer have lines on the side of the monitor. The horizontal centering tabs didn't seem to make a difference.

Thank you.
 
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If that game is a "keeper" for you, you should rebuild that monitor. I can tell from the pics it has low quality caps and an original flyback. It's going to go at some point. you could just play it until it does, or be proactive and get it rebuilt.

I'm glad the h-freq pot suggestion panned out.
 
If that game is a "keeper" for you, you should rebuild that monitor. I can tell from the pics it has low quality caps and an original flyback. It's going to go at some point. you could just play it until it does, or be proactive and get it rebuilt.

I'm glad the h-freq pot suggestion panned out.

How do I go about doing that? Do I send the board away to someone with skill to do that?

And yes, the game is a "keeper", and it's all original. It came from my best friends fathers pizza place and then sat in his garage for 20+ years. It's really good shape with very few marks on the side art.

Attached is photo of screen after adjustment.
 

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