Lenovo ThinkPad T21 T20, T21, T22, T23 - Hardware Maintenance Manual (April 20 - Page 60
LCD-related symptoms, Important
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Symptom-to-FRU index LCD-related symptoms Important The TFT LCD for the notebook computer contains many thin-film transistors (TFTs). A small number of dots that are missing, discolored, or always lighted is characteristic of TFT LCD technology, but excessive pixel problems can cause viewing concerns. The LCD should be replaced if the number of missing, discolored, or lighted dots in any background is: v XGA: 8 or more bright dots, 8 or more dark dots, or a total of 9 or more bright and dark dots. v SXGA+: 11 or more bright dots, 13 or more dark dots, or a total of 16 or more bright and dark dots. Note: A bright dot means a pixel is always on (white or color.) A dark dot means a pixel is always off (black color.) Symptom or error No beep, power-on indicator on, and a blank LCD during POST. v LCD backlight not working. v LCD too dark. v LCD brightness cannot be adjusted. v LCD contrast cannot be adjusted. v LCD screen unreadable. v Characters missing pixels. v Screen abnormal. v Wrong color displayed. Horizontal or vertical lines displayed on LCD. FRU or action, in sequence System board. 1. Reseat the LCD connectors. 2. LCD assembly. 3. System board. 1. See important note for "LCD-related symptoms." 2. Reseat all LCD connectors. 3. LCD assembly. 4. System board. LCD assembly. 54 ThinkPad T20, T21, T22, T23 (MT 2647/2648)