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NeoGeo mvs-4-25 (WG K7000 compatible chassis?) w/ color separation, size issue
Sememmon:
Hello!
I've got a Neo-Geo mvs-4-25 with a Zenith tube and, I think a WG K7000 (or compatible) chassis based on reading the description here http://www.homearcade.org/BBBB/monitor78.html . The board on my chassis has no discernable identification, but the ICs (7823 & 1397) do match the description and the board looks very similar to the one in the photo. There's also a K7000 built by Zenith there as well http://www.homearcade.org/BBBB/7000z.html that could be it, hard to tell from the picture.
Here are some (less than stellar) photos of my monitor / chassis: https://photos.app.goo.gl/aXAJ5Q2G2T5b85L97
Anyway, the original issue that started me down this monitor rabbit hole is that at the top-left corner of my monitor, I have color separation. It is visible in the cross hatch test in my photo album above. I know nothing about CRTs. What would cause that? How can I fix it?
In addition, the horizontal size of the image is too wide for the monitor. To avoid having a wrapped-around-like bar on the right side of the screen, I have to move the position as far away as I can. However, this causes things on the left edge (and still somewhat on the right) to be off screen. Is there a way to shrink the image width a bit?
Lastly, I'm always reading/hearing about cap kits being a fantastic thing. Given that these are the only issues my monitor is experiencing, would a cap kit still help? Is there anything else I should be doing to maintain the life of my monitor? I'm thinking of at least pulling out the chassis and cleaning it, so any other service I can do would be great. I've popped/discharged it before with a grounded flathead .. and I know my way around a soldering iron, so not too worried about any of that.
Any help / advice / info would be greatly appreciated! Thank you.
-Sem
lilshawn:
this does not look like a WG chassis to me. this looks like one of the many sharp image (or it's knockoffs). I can't be certain, as I've only actually had to fix 2 or 3 sharp image monitors in the last 10 some odd years.
your separation in the corner as you call it (called convergence) is somewhat normal for an analog monitor like this one.... it's fairly typical to have some convergence issues in the corners. sometimes little magnets are placed around on the tube to help direct the beams properly and perhaps one has fallen off. check the surface of the tube for evidence of tape residue or glue that may have held something to it.
it's tough to get a perfect image, especially with these old analog monitors. You really need a microprocessor controlled deflection system to really get a perfect image. trust me, once you get a game on there and you are playing it, you will never notice the convergence issue, and in all seriousness, it's not that bad.
as for your width issue... if you have the ability, change out those capacitors. it could be the cause. the capacitor used for tuning the width are very small value and if they are old and starting to drift off, it can make it too wide, or completely unadjustable.
Sememmon:
Thank you for the response! I've actually just lived with the separation for quite a long time. As you said, it's just a minor annoyance. However, I recently decided to learn more about my cabinet and clean it up. I believe that the tube has a coil all the way around it? Maybe that has something to do with it? I will take a look for missing magnets as you said.
Sounds like the cap kit would be a good thing. So, would it be the WG K7000 kit? That Sharp Image link I shared seemed very similar (including the ICs). I was figuring that'd be the kit I needed.
Thanks for the help!
lilshawn:
the coil all the way around it is called a DEGAUSS coil. it temporarily passes mains voltage through a coil of wire looped many times around the tube.
When the monitor is first powered on, the power flowing through the coil is great, and a huge alternating magnetic field is produced... then after a few seconds (using a circuit) reduces the power flowing through to coil down to nearly zero essentially turning it off. what this does is demagnetize the screen. magnetization can happen if the monitor is moved or turned while powered on... or a magnetized piece of metal goes near it. typically low magnetizations can be removed this way, while larger color distortions (like from magnets being brought to the screen) require a larger, more powerful degausser. I, for instance have a handheld plastic hoop about 12 inches in diameter with a power switch that I can manually activate and blast a screen to eliminate stray magnetic fields.
Sememmon:
Thanks for the info about the degauss coil. I had a hunch about some of that, but good to know how it all works.
Which cap kit should I get?