Why do some Apple color monitors have a thin line or lines across the screen?

The CRT has a specially constructed aperture grill which improves its convergence and produces a sharp and clear image. The aperture grill is a grid of vertical wires located just behind the CRT screen. These CRTs require a horizontal stabilizing wire or wires to help support the aperture grill. The supporting wires, which are thinner than a human hair, stabilize the aperture grill against shocks.

Typically, displays with a viewing area of 15 inches or less have a single horizontal grid wire approximately one third from the bottom of the display image. Displays larger than 15 inches typically have two wires, each about one-quarter to one-third of the way from the top and bottom of the display image.

The lines are common to all tron style displays, and are not screen defects. Their presence cannot be adjusted out or eliminated by repairing or replacing modules in the display.

These Apple products include a tron style CRT:

• 13-inch High Resolution RGB Monitor
• 14-inch Macintosh Color Display
• Multiple Scan 17 and 20 Displays
• AppleVision 1710 and AppleVision 1710AV Displays
• Macintosh 16-inch Color Display
• Macintosh Color Classic
• AudioVision 14 Display
• Macintosh TV
• Macintosh LC 520, 550, 575
• Performa 550, 560, 575, 577, 578
• ColorSync 17-inch Display
• ColorSync 20-inch Display
• AppleVision 750 Display
• AppleVision 750 AV Display
• AppleVision 850 Display
• AppleVision 850 AV Display
• Apple Studio Display 17 (16 inch viewable image size)
• Apple Studio Display 21-inch (19.8-inch viewable image size)