My screen needs to twist a little... How to adjust on CH288???

[shan1784]

I've got a Makvision 2425 25" arcade monitor... I can't find anything on this monitor... I've adjusted everything that I can identify.. So now the brightness, focus, Verticle and horizontal holds are good... The Verticle size is good but the horizontal size is giving me issues...

My screen is twisted just a tad that if I adjust the width to the very edges of the screen the top right and bottom left of the picture hangs off the screen... If I could adjust the rotation I could fix this but don't know how to pull this off... I've adjusted the pincushion but it doesn't help... I mean it adjusts the picture where the sides are even but the the whole left side hangs off and I can't adjust the horizontal size anymore to bring it in...

There is another coil by the horizontal width coil that I tried to adjust but it doesn't seem to do anything... I had to use an Allen wrench to adjust it where the horizontal width coil was just a little knob to turn...

I've emailed the manufacturer twice now on separate questions and each time they basically said it was discontinued and they no longer support it...

I should also note that I just installed a cap kit over the weekend, but this issue was there before that...

Any ideas would be appreciated..

[lilshawn]

Assuming it's not epoxied on, you can power it off, loosen the yoke (it has a small clamp or screw holding firmly in place.) And give it a slight rotate. And I mean SLIGHT. You should be able to straigten out the picture

[shan1784]

I did some more research today and found the following post -

http://forum.arcadecontrols.com/index.php?topic=93335.0

This is basically the same issue I'm having... I too have the ch288 board as well except mine has one additional adjustable coil located at the yellow circled area shown in the picture below... This is the one I adjusted for the horizontal width.. At least that is what was changed when I turned it...



So not sure what the other coil does.. I tried to adjust it last night with an allen wrench but  nothing happened.. Not even sure if it turned or if my wrench didn't fit and just was spinning freely...

So for the other post I linked to above it was mentioned to replace the horizontal width pot on the remote boad with one of a slightly higher value.. According to the schematic I found it is a 5K pot right now so I was thinking of replacing it with a 20K pot and see if I can get some more room to pull the width in and then use the pincushion pot to even up the sides...

Does that sound like a plan???

[shan1784]

Well that didn't make a bit of difference...

I really hate to loosen the clamp and straighten it that way... I thought that could jack up some other things, am I wrong on that?

[lilshawn]

this chassis does not have the ability to fix a rotated image. Rotation adjustment wasn't added until way later on. rotation requires an additional coil of wire that runs around the tube just in front of the yoke.

Well that didn't make a bit of difference...

I really hate to loosen the clamp and straighten it that way... I thought that could jack up some other things, am I wrong on that?

only if you start going crazy. say your image is a 1/4 inch out between the top left and the top right, you only need to rotate the yoke like a 1/2 a degree. it's not much.

if you start messing with the convergence magnets and the tilt wedges on the yoke, you will start having issues.

all you're going to do is loosen the clamp, rotate the yoke 1/16 of an inch in the direction of the high side of the image, and tighten it back up.

the only ways i can see this going bad on you:

1:) the yoke is bonded onto the tube and you can't move it.
2:) the area on the yoke where the clamp squeezes onto the neck of the tube is broken (which might be why it's tilted now.) you will have to align it and glue it.
3:) you don't loosen the clamp enough and you end up with #2
4:) you reach in and grab hold of something that is not the yoke (like the convergence rings) and twist them out of alignment.

[shan1784]

Ok, that is understood...

Here is a pic of my actual board...




And just for my refrence, in the pic below and circled, is this what I am suppose to loosen and turn to get the screen straight? And when I do this what should I grab onto to actually turn? I want to make sure I'm twisting the right thing...

[Rickn]

Yes lilshawn is giving you good advise!

There is no rotation coil or control.

Sometimes you can give the yoke a slight twist without loosening it, but keep in mind I have done thousands of these type adjustments.

Do not touch the purity/convergence rings.
Just loosen the yoke clamp slightly and grab the outside palstic part of the yoke and give it a slight twist.

I do it with power on but again I have been doing this for years you may not want to!

if you were local, I would be happy to do/show you how.

Rick

[shan1784]

Thanks for the replies on this guys, I really appreciate it...

So in my picture above is what I have circled in yellow what I have to loosen? And the plastic piece you speak of that I actually grab onto to turn, is that the white piece that the clamp is around?

Also the rings you say not to touch are those the gray ones just on the outside of the circle to the left?

[Rickn]

Yes that is the clamp, but when you try to rotate the yoke, grab it at the outside where the metal tabs are.

If you do it power on, then keep away from the red and blue yoke leads, they bite.

good luck

Rick

[shan1784]

Ok, I apologize, I'm still not sure on where to turn it at...



Do I grab what's circled in yellow or red?

Again, thank you for your patience and assistance...

[Rickn]

Still ahead of the red circle. Grab the yoke where those 4 metal tabs are and give it a slight twist.

If you are still not sure, call me amd I will try to walk you through it.

Rick

519-621-1722

[shan1784]

Wow, much appreciated... I'll give it a shot and see if I can get it... I should be able to... I'll let you know... Thanks for the info again...

[shan1784]

Looks like I got it now... Not 100% perfect but I decided not to push my luck... It is hardly noticeable now so we are happy... Thanks to both of you for the help...

[lilshawn]

 

now that you know the first of many secrets of the monitor grasshopper, you shall pass them to another when the time is right!

[shan1784]

Lol, sure thing...