How to Focus a Rear Projection TVby David Lipscomb
Rear projection televisions utilize three cathode ray tubes to project and combine the images on the back of the TV's screen. These tubes, like any device using a lens, can lose focus from vibration and natural drift. Projection TVs use focus pots, three small knobs on the front of the TV designed to allow a user or technician to focus these projected images and form a cohesive image. The objective is to create a sharp, crisp image.
Pull off the front speaker grilles on the television. These are typically held on with heavy-duty hook and loop connectors.
Unscrew the Phillips screws holding on the control panel. Remove the front control panel, housing the buttons on the front of the TV. Let the panel hang to the side, out of the way.
Locate the focus pots directly in front of you. Use the TV's remote to turn on the convergence crosshatch test pattern, built into the set. Consult the owner's manual for specific steps if required. Use a small flat-head screwdriver to carefully remove any hot glue that is holding the focus pots in place.
Observe any fringing that is occurring on the crosshatch lines. This will be any color appearing to tint or create fuzzy edges on the sides of the white lines constituting the crosshatch.
Turn the individual pots one by one, isolating and correcting each color individually. Rotate counterclockwise to refine the line; rotate clockwise to fatten it. Remember that each convergence line must appear perfectly white with no color fringing for the focusing to be deemed accurate.
Add a small drop of hot glue to one side of each focus pot to help keep the correction in place. Replace the control panel and grilles.
- Turn off the lights to increase visibility of each convergence line.
- Reduce contrast to about 40 percent to prevent image retention due to the high contrast crosshatch lines on screen.
- Be very careful inside a rear projection TV. Dangerous voltages reside on the chassis in certain areas.