Strange Shadows Cast by Windows

Question

Hi, everybody,
I have recently begun to experience a very strange phenomenon on my old iMac DV 400mhz.
First, a little background. The unit is about 10 years old, has an upgraded 120 GB hard drive, and has 768 MB of RAM installed. I am currently running Mac OS X 10.4.11 Tiger, and I have a number of applications installed, including, most recently, the Gimp photo shop program (which works through the X11 shell).
Now, to the problem. Within the last few days, I've noticed what seems to be a faded ghosting effect on the right side of the screen. It is visible to the right of most open windows and menus, and is most starkly visible on the boot screen.
Included below are a few sample pictures that will illustrate what I'm talking about.
[http://img228.imageshack.us/img228/3908/powerup.jpg]
[http://img43.imageshack.us/img43/5356/findermenu.jpg]
(Taken with my iPhone)
I am puzzled because when I take a screen capture, none of the shadows show up -- as you can see in this picture:
[http://img32.imageshack.us/img32/6597/finderscreen.jpg]
This leads me to believe that there is something happening to my monitor. I guess my question is, "What could that be?"
I've already repaired Disk Permissions, Verified the Disk, reset the PRAM, and started up from the Mac OS X Install Disk, and the strange shadows are still visible. I even used the calibration assistant in System Preferences. Does anyone have any idea about what's happening? Has this happened to anyone else? Is my monitor finally starting to die after 10 years? Is there something else I'm missing?
I'd appreciate any help that you guys can provide. I've always enjoyed this forum community in the past, and I hope to communicate warmly and helpfully on a more regular basis in the future.
Thanks!
Sammy Larkin

Answer 1

If you look carefully at the LEFT side of the white box in the "Starting Mac OS X" screenshot, there is a magenta cast all up and down the left side, a bit more pronounced at the bottom of the box. This says to me that your display has color convergence problems (all the electon guns are not aimed at quite the same spot to give pure white everywhere). \[White areas are formed by lighting up adjacent Red, Green and Blue phosphor dots on the screen. If the convergence is not quite right, areas that should be white will have color casts.] I think that the shadow you see is an echo of this color mis-alignment.
This is a physical problem inside the CRT, nothing to do with software. That is why your screen shot looks great, despite the defects of the picture on the display.
This can happen whether the display uses three electron guns shooting at clusters of dots (Tridot) or a single electron gun shooting at alternating stripes (Trinitron) technology. Yours may be a Trinitron, as it appears to have the tiny imperfections, narrower than a pixel high, that extend all the way across the screen near the top and bottom, and possibly a few more. These are caused by the tiny wires that support the aperture grill used to mask off stray electrons in a Trinitron display.
On your display, I do not know offhand whether color convergence is something that can be changed under software control. On many large (21" and up) SONY displays, there are controls in the software or on the front panel that can be used to adjust the color convergence.
If there are no such controls, the display may have to be opened, and adjusted with the power on and covers off. This may expose the technician to upwards of 10,000 Volts, and should only be undertaken by those trained in proper safety procedures. It can be very dangerous. Connecting that Voltage across your heart (e.g., Hand-to-hand) can stop your heart.