The
proper procedure for adjusting white balance is covered in the service manual
for each model. A color analyzer is required to properly set the X and Y values
of each of the color temperature settings. The steps required to perform this
adjustment varies from model to model. It also varies between a direct-view and
projection unit. Because of this, it would be impossible to cover the
requirements in a general sense. Each type of unit has a unique procedure for
the initial setting of brightness, contrast, and what color temperature to
start with. Some direct-view LCD models have an adjustable backlight that must
be set to a certain level. The procedure for reading color balance from the
screen also varies for a projection or direct-view model.
Many technicians will not have the luxury of
carrying a color analyzer. They are
expensive ($4000 and up) and require training to use properly. In cases where
color balance must be adjusted and an analyzer is simply not available, there
is a procedure that can be performed that will produce satisfactory results.
Although not nearly as accurate, it is better that not doing the adjustment at
all. This procedure should only be done if it is absolutely necessary and a
color analyzer cannot be acquired.In cases where a color analyzer is not available, white balance can be aligned by eye. Technicians who are experienced with adjusting CRT-based displays will be familiar with this procedure. They are similar except that CRT’s require that the G2 grid (screen) be adjusted to the point of stopping the electron emissions from the cathode at reference black. Drive controls are then adjusted to make each cathode emit the proper level of electrons at high brightness to achieve a white raster.
When
adjusting an LCD display, there are no cutoff adjustments. In this particular
model, the Sub-Contrast adjustments are used to adjust white balance for the
bright areas of the screen. The Sub-Brightness adjustments are set for the
low-level brightness areas.
The
best test pattern to use when visually adjusting white balance is a monochrome
stair-step pattern versus a 100IRE white screen. This provides a view
throughout the range of brightness levels the display will generate. Another
significant difference in the adjustment procedure is starting with the
“Neutral” picture setting. The “Warm” setting shifts the white balance towards
the red end of the scale whereas the “Cool” setting shifts towards the blue
spectrum. By using “Neutral”, the white balance can be adjusted visually. This
provides a reference for the eye so that the “Cool” mode can be set with the
Blue Sub-Brightness and Contrast increased slightly to boost the color
temperature to around 9300K. The “Warm” setting will have more Red Sub-Brightness
and Contrast levels to create
a white balance in the 6500K range. “Neutral” should fall into the 8000K level.
Be
certain to leave the low-bit data settings for the Green Sub-Brightness and
Contrast to zero. The high-bit data should be in the mid range. Adjust the Blue and Red data to achieve white by adding
these colors to the green. The following procedure can be used for a unit when
the white balance is significantly off:
- With the unit in “Neutral”, set the brightness level to one-third and the picture level to two-thirds. Input a monochrome stair-step pattern with at least 75IRE at the highest white level.
- Check that the Green Sub-Contrast and Brightness levels are set to mid-range for the upper-bit data and zero for the lower-bit data.
- Set the Red upper-bit data for Sub-Contrast and Brightness to mid-range and the lower-bit data to mid-range.
- Set the Blue upper-bit and lower-bit data for Sub-Contrast and Brightness to zero. The picture will now be a yellowish/green.
- Adjust the Red Sub-Contrast Low to generate a yellow color at the brightest portion of the test pattern. If you find that you are reaching the extreme end of the data range (0 – 255), set the Red Sub-Contrast High up or down one number and try again.
- Once the bright video level is closest to yellow as possible, repeat the above procedure for the Red Sub-brightness adjustments.
- When satisfactory yellow is achieved throughout the video range, set the high-bit data for Blue Sub-Contrast and Brightness to mid-range. Adjust the low-bit data for each to change the yellow screen to white. If you are at either of the extreme ends of the data ranges (0 – 255), set the upper-bit data up or down accordingly.
- Once the “Neutral” white balance is satisfactory, adjust the “Warm” white balance in the same way. Add a small amount of extra Red Sub-Contrast and Brightness. “Cool” is adjusted adding a small amount of extra Blue Sub-Contrast and Brightness data.
Although the above procedure can be somewhat
subjective, it has worked rather well for CRT-based consumer televisions for
many years. It is a viable alternative when a color analyzer is impossible to
acquire.
