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Author Topic: Image Bending and Discoloration on Left Side of Screen  (Read 153 times)

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chanson8118

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Image Bending and Discoloration on Left Side of Screen
« on: March 23, 2020, 05:24:03 pm »
I recently refurbished an old Ultracade cabinet, and while it is mostly all set there are still a few issues with the screen that I just can't seem to fix.

Full disclosure, I am a novice at all of this but have done considerable research online to make it this far.  The issues I'm having seem very similar to others I've seen referenced, but they are different enough that I would like to see if anyone else has resolved exactly what I am experiencing.

The monitor is a Wells Gardner K7400 25", which is connected through a VGA breakout cable to an ArcadeVGA 5000 Graphics Card installed in a Windows 7 PC.

The first issue that I noticed was a "bowing" of the screen, only on the left hand side.  While this was only really visible in games with a narrow screen image projected, like 1942 for example, I just had to try and tinker with it. The best resource for information that I found was a document titled "A Guide to Setup and Adjust the CRT of an Arcade Color Monitor" by Ingvar Karlsson.  While he, and others, referenced a "Pincushion Distortion", since my issue is only on one side of the screen that doesn't seem to be what I am dealing with.  The document detailed many adjustments well beyond my comfort zone, but I did try his method of making and using Yoke Strips to try and fix the dynamic convergence on the left side, but to no avail.  He also referenced the use of refrigerator grade magnets on the back of CRT's to help with convergence issues.  This second method scared me so I just had my son slowly move a fridge magnet toward the back of the tube on the problem side to see it's effect, but as he got close the image just distorted more and I had him stop.  This weak magnet was in close proximity to the back of the tube for less than three seconds.

After my failed attempt at fixing the bowing on the left side of the screen I started to notice that the left side was also discolored/faded.  I'm not certain if I caused this myself trying to fix the first problem, or it's part of the original bowing problem that I just didn't notice before.  My guess is the former.  I'm attaching images of the issue(s).  The solid blue looking screen is actually the grey screen when the PC is off and only the monitor is on.  The discoloration is effectively a faded blob on the left of the screen.  It's not overly noticeable when there is a lot on screen, but solid colors show it clearly.   I'm also including an image of a test pattern that shows how the white and red lines are not in sync on the left side of the screen.  This image also shows how the white lines are not as vibrant on the left side.

I have read up on degaussing, and frankly between how hard it seems to get my hands on a coil, and the thought of putting a magnet near my monitor again makes me wonder if it's the way to go.  I've turned the screen on and off many times in the hope that the built in degausser would do the trick, and even unplugged it and let it sit cold for 48 hours between cycles at one point, but no luck.

Any advice for how I should proceed would be greatly appreciated.