25k7401 issue, need help

[Popcorrin]

I have a Wells K7401.  Everything is working well for the most part; stable picture, good colors, but there is one problem.

I will try to explain it best I can. There seems to be some frequency interference causing some rolling over top of the image(not the image itself, it's stable).  It's not real noticeable until you focus on it.  The rolling will go up then change directions and roll down, at other times it comes to a stop and then starts again.  It doesn't distort the geometry of the image or anything like that.  It's similar to what happens to some televisions when you run the vacuum cleaner or microwave, maybe not as noticeable and it doesn't move at a steady speed in the same direction like with those things.

I plugged it into different outlets to make sure it was grounded well, and I made sure that all the other electrical devices were turned off. 

[modessitt]

I wouldn't say that trying different sockets would prove it was grounded well.  If you want to verify your wall current is stable, put a meter on it to see if your voltage stays steady.

Does your plug have 3 prongs?  If not, that could be your problem.  I've even seen the center prong crack and not connecting properly.

You may try disconnecting first your marquee light (if it's on) and your speakers to verify you're not getting feedback from either.

I would then make sure your fuses are new, clean, and tight.

And last but not least, make sure your monitor input wires are not routed too close to either the flyback or the yoke.  I've seen this problem sometimes due to a little magnetic interference to the color and sync lines.

Just some things to try.  These are the easiest things to check, then we can try the harder stuff.....

[Kevin Mullins]

Does the power cord run through an EMI Filter in the bottom of the cab?
(usually a little silver square can looking thing)

[flashdog]

Could be from your switching power supply. Try making a little jumper and put it on the ground connection and to the FG or field ground on power supply. Also you can add a ground to the monitor frame, if it doesn't already have one. Good luck!

[Popcorrin]

I tried everything modessit suggested and the power is running thru an emi filter.  I still am having issues.  I will try running another ground to the monitor frame as flashdog suggested. 

I do have a question for you guys.  Could a component on the chassis be causing this or is it most likely some outside interference?

Thanks.

[modessitt]

Sometimes you can get frequency interference if you have something else plugged into the same socket/power strip or even along the same wall/room.  Very similar to how lights would dim when you turned on your hair dryer.  Or how your computer speakers will buzz just before your cell phone rings.

I had a monitor that kept giving intermittent, tiny vertical lines.  Turned out to be caused by a blinking neon light that was plugged into the same power strip.  Unplugged the light and problem went away.