Electrical Characteristics Questions
- My LCD has a line out. What caused this and what can be done about this?
- My display has a bright green dot that stays on all of the time. What can be done to eliminate this?
Q. My LCD has a line out. What causes this and what can be done about it?
A. Typically there are row drivers and column drivers that burnout and cause a given row or column not to be addressed - simply stated, it is not connected electrically any more to the display. If a block of lines goes out, the entire driver has probably been damaged. One possibility is that the TAB driver has disconnected from the surface. The TAB driver is connected to the transparent traces on the glass using an anisotropic conductive film (ACF). Sometimes that film will be damaged and a particular connection between a row and a column in the driver can be destroyed. If you have a row or a column driver damaged, the driver needs to be replaced. In a CG silicon display where the driver is on the glass there is no repair. Chip-on-film drivers can be replaced in their entirety.
The real issue is what causes these failures. They are typically caused by electrostatic discharge. You should make sure that your manufacturing area is properly handling displays especially before they are connected to a ground. Make sure that personnel handling displays are working with wrist straps and are working on a conductive floor. An ionized air flow environment with a slightly elevated humidity is recommended for handling displays that are not yet grounded in a system. When removing protective plastic film, remove in the direction away from the drivers and should remove it at a relatively slow rate to eliminate the build up of a strong static charge on the display. When these precautions are taken, you should see minimal or no damage to row or column drivers and most line-out problems will be eliminated.
Q. My display has a bright green dot that stays on all of the time. What can be done to eliminate this?
A. The state-of-the-art for making active-matrix displays of causes some level of pixel defects both dark pixel defects and bright pixel defects. Bright pixel defects (particularly green) are most objectionable because the eye is most sensitive to green light. We are currently making efforts at the factory to attain even higher levels of cleanliness to minimize the number of bright pixel defects. But eliminating them entirely is not possible for any manufacturer making conventional twisted nematic displays. We are now making displays with the Advanced Super View process that are normally black instead of normally white. In this case, a dead transistor will cause a dark pixel defect instead of the more objectionable bright pixel defect. It may be possible for certain panels to become bright pixel defect-free after time. Once a pixel defect occurs there really is no repair. This a defect is caused by conductive contaminant inside the liquid crystal active-matrix array where a conductive particle becomes a bridge between the source and drain layers of a transistor and will then always be on.
There have been attempts to make repairs with lasers, but it's not always effective and there is no such service available today. Refer to the product inspection standard for the number of bright pixel defects that are allowed. These defects are a characteristic of all amorphous silicon displays. It is a trade-off that you're making for higher contrast and better saturation.