Pixel failure is defined as one or more pixels that fail to pass light, are always passing light, or intermittently cause either of the previously mentioned symptoms. One must be extremely lucky to experience an LCD panel with zero pixel defects. A typical Sony LCD Projection unit utilizes 3.28 million pixels between the three LCD panels. LCD panels with zero defects are possible to manufacture, but it would require rejecting a large amount of them and that would make the cost rise to an unacceptable level.
Determining whether a particular LCD panel requires replacement due to pixel failure is a somewhat subjective procedure. No official specifications exist due to the various LCD panel manufacturers due and violations of non-disclosure agreements. Combining several common sense criteria can help determine if the pixel issue warrants a panel replacement (the entire optical block for a projection unit).
A
pixel that is continuously lit is far more obvious than one that never lights.
The color of the pixel that is “stuck on” is also important. The eye is the
most sensitive to green, somewhat to red, and very little to blue.
The
number of defective pixels is also important. If only one pixel is out then
99.99999% of the pixels on the panel are operating properly. This is quite
acceptable. As several or more pixel failures are approached, the next criteria
are of importance.
The area of the pixel failure will determine how
easily it is noticed. Pixel failures in the center area of the screen that
constitutes 1/3 of the screen are more noticeable than those in the outlying
areas. This is where the customer is concentrating his viewing.
As
can be seen, pixel issues can be somewhat ambiguous. The greatest problem to
deal with is that once the customer has found a defective pixel (or pixels)
they are going to dwell on it. The following is a generalized approach that
should assist the technician in dealing with a customer who is complaining
about pixel problems.
Try not to let the customer show you where the
pixel failure(s) are. Tell the customer that you would like to view the picture
for a moment with an active video signal. It is during this period of time that
the technician should attempt to locate any defective pixels. If one cannot be
found easily, the panel is probably acceptable and should not be replaced. If
one or more pixels are easily spotted, the panel should be replaced. Handle
each pixel issue on an individual basis.DUST
Dust will always be an issue with projection LCD devices. Large amounts of air are needed to pass around the lamp, lenses and mirrors to keep the LCD panels cool. When dust becomes and issue is dependent on several factors such as environmental conditions, cumulative hours of use, etc.
Dust particles will appear as dark spots that are larger than the size of an individual pixel. It must first be determined if the particle(s) are on the LCD panels or the screen. The simplest way to do this is to grab the top of the screen and rock it back and forth a small amount. If the dust is on the LCD panel, the spot(s) will move to different locations on the screen. If they follow the rocking motion of the screen, the dust is on the backside of the Fresnel lens assembly. It could also reside between the layers of the screen. Doing this helps to determine if the screen or the optical block requires cleaning.
Dust
on the LCD assembly or the screen are not covered by the warranty. Under normal
conditions, noticeable dust may appear well out of the warranty period and
should be considered as normal maintenance like any other type of projection
television. Dust accumulating on the rear of the screen is easily cleaned using
a soft cotton cloth and water. The use of paper towels or tissues is not
recommended since these tend to scratch the surface.
Cleaning
of the LCD panels requires more time. The optical assembly must be removed and
access gained to the panels. This will require the removal of the LCD driver
board. Blowing a low-pressure stream of compressed air may remove the
particles. In some cases, such as a large number of dust particles, simply
blowing air into the cavity that houses the LCD panels only moves them to other
areas of the panels. In this case it will be necessary to remove the LCD panel
assembly.
CAUTION: Handle the LCD assembly with extreme
care! Although the LC panels are durable, it is possible to knock one or more
of the panels out of alignment. This would cause a mis-convergence of the
colors on the screen. It is very difficult to realign the panels. Check the ESI
website on a regular basis to see if any up-to-date service routines have been
posted regarding this procedure.