How to fix a dim iMac CRT: "2. Badly Adjusted Cathode Ray Tube: The second major cause of unsatisfactory screen performance is a maladjusted CRT. Symptoms are usually less severe than with bad firmware, but are highly annoying nonetheless. They include fuzzy, out of focus areas on the screen (sometimes the at center but not the sides, or vice versa), excessively dark screens, or excessively bright, washed out screens. You may notice, while watching a DVD, that parts of a scene that should be in shadow, but still clear, are instead completely black. Or you may notice that even with the monitor brightness set to the max, digital photos appear dark and underexposed on the iMac screen, but not on other computers. Brightness (voltage) and focus are adjusted via two screws on the high voltage flyback transformer on the left side of the iMac, just below the edge of the upper plastic shell. The adjustment is not difficult, but should be performed with extreme caution. Even when the monitor is powered off and unplugged, it still holds enough charge to kill you instantly. IF YOU ARE UNCLEAR OR UNCERTAIN OF WHAT YOU ARE DOING, STOP! TAKE IT TO A CERTIFIED APPLE REPAIR TECHNICIAN."