A tape automated bonding fault is a defective pixel caused by a connection failure from the TAB that connects the transparent electrode layers to the video driver board of an LCD.
TAB is one of several methods employed in the LCD-manufacturing process to electrically connect hundreds of signal paths going to the rows and columns of electrodes in layer 6 (the transparent electrode layer) in the LCD to the video integrated circuits (ICs) on the driver board that drives these electrodes.
If an LCD is subjected to physical shock, this could cause one or more TAB connections to fail inside the display. This failure is often caused by horizontally flexing the chassis (e.g. while wall-mounting or transporting a display face up/down) or simple failure of the adhesive holding the TAB against the glass. TAB faults require the replacement of the LCD module itself. If these connections were to fail, the effect would be that an entire row or column of pixels would fail to activate. This causes a horizontal or vertical black line to appear on the display while the rest of the display would appear normal. The horizontal failure runs from edge-to-edge; the vertical failure runs from top-to-bottom.
Hardware manufacturers and distributors tend to claim that TAB faults, as opposed to other physical defects that may be found in an LCD, do not allow for repair.