Panasonic TC-22LH1 Technical Guide
Technical Guide
TC-22LH1
LCD Television
Technology, Troubleshooting, &
Adjustments
Panasonic Services Company
National Training Center
Produced by
Gerald Gaimo &
Jean Magloire
Panasonic Services Company
National Training Department
Secaucus, NJ
Warning
This service information is designed for experienced repair technicians only and is not designed for use by
the general public. It does not contain warnings or cautions to advise non-technical individuals of potential
dangers in attempting to service a product. Products powered by electricity should be serviced or repaired
only by experienced professional technicians. Any attempt to service or repair the product or products
dealt with in this service information by anyone else could result in serious injury or death.
Table Of Contents
2
Introduction ........................................................................................................ 5
Chapter 1 Technology Explanation .................................................................. 7
1.1 Properties of Liquid Crystals..................................................................................7
1.2 LCD Basic Reflective Assembly.............................................................................8
1.3 Backlighting vs. Reflective.....................................................................................8
1.4 Color......................................................................................................................9
1.5 LCD Addressing Technology...............................................................................10
1.6 Backlighting .........................................................................................................11
1.7 Inverter Power Supply ......................................................................................... 11
1.8 High Voltage Power Supply.................................................................................12
1.9 Test and Measurement........................................................................................13
1.10 Features ............................................................................................................14
Chapter 2 Circuit Descriptions........................................................................ 16
Block Diagram Overview ...........................................................................................18
Chapter 3 Video Circuit Explanations ............................................................ 20
Video Signal Block Diagram......................................................................................20
NTSC Video Signal Path ...........................................................................................22
ATSC Video Signal Path............................................................................................23
HDMI Signal Path......................................................................................................24
Picture Processing.....................................................................................................25
Resizing The Screen ................................................................................................. 27
Chapter 4 Audio Circuit Explanations............................................................ 28
Audio Signal Block Diagram......................................................................................28
Multiplexed Television Sound (MTS)........................................................................29
Surround Sound Processing......................................................................................31
Power Supply Section................................................................................................32
Chapter 5 Unit Disassembly ...................................................................34
Rear Cover Removal.................................................................................................34
AP Board Removal....................................................................................................35
DV Board Removal.................................................................................................... 36
DG Board Removal....................................................................................................36
B1 Board Removal.....................................................................................................37
H Board Removal ......................................................................................................37
Speaker Removal......................................................................................................38
K Board (Button Board) Removal ..............................................................................38
V Board (remote sensor) Removal ............................................................................39
LCD Panel Removal.................................................................................................. 39
Chapter 6 Self Check and Adjustment ........................................................... 41
Self Check.................................................................................................................41
Service mode Adjustment..........................................................................................42
Main Adjustment SUB Adjustment.............................................................................43
3
SUB Adjustment ........................................................................................................44
LCD Pixel Specifications............................................................................................45
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Introduction
The information provided in this document is designed to give the technician a brief
overview of the LCD display technology. It is also intended to help the technician
diagnose and identify the defective printed circuit board, efficiently. This guide covers
the Panasonic TC-22LH1 LCD television. Troubleshooting flow charts, signal path
diagrams, and connector information are included to provide enough details, so the
technician could accurately determine which of the boards contains the source of the
problem. Alignment and adjustment procedures are also included in this document to
complement the information available in the service manual.
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6
Chapter 1 Technology Explanation
1.1 Properties of Liquid Crystals
Liquid Crystals exist in an unusual state that is somewhat like a liquid and a solid. The
molecules in this state tend to maintain their orientation like molecules in a solid but also
move around to a different position like a liquid. There are several distinct phases of
liquid crystals, dependent upon how they are used.
A twisted nematic (TN) LC display consists of two polarizing filters, two pieces of glass,
some form of switching element or electrode, which is connected to a power source as
depicted in Figure 1. An applied voltage is used to untwist one pixel.
Figure 1
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1.2 LCD Basic Reflective Assembly
Figure 2A represents a basic LCD assembly, which is comprised of the following: A
mirror (A), which is located on the rear of the assembly, provides for the reflection of
light. A piece of glass (B) layered with a polarizing film is coated on the bottom side of
the mirror, and a common electrode plane (C) made of indium-tin oxide is placed top. A
common electrode plane covers the entire area of the LCD. Above that is the layer of a
liquid crystal substance (D). This is followed by another piece of glass (E) with an
electrode in the shape of a rectangle etched on the bottom side. Another polarizing film
(F), which is layered on top, is right angle orientated to layer (B). A power source is
connected to the electrode. When no current is supplied to the electrode (E), light
entering through the front of the LCD will be reflected off the mirror and bounce right
back out. When current produced by the power source is applied to the electrode (E),
the liquid crystals between the common-plane electrode and the electrode shaped like a
rectangle untwist and block the light in that area from passing through. The rectangle
ithin LCD appears as a black area. w
Figure 2a
1.3 Backlighting vs. Reflective
Most computer displays are lit with built-in fluorescent tubes above, beside and
sometimes behind the LCD. A white diffusion panel behind the LCD redirects and
scatters the light evenly to ensure a uniform display on its way through filters, liquid
crystal layers and the electrode layers. By adding to the layer that contains the single
electrode, more enhanced displays can be designed.
Figure 2b
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1.4 Color
An LCD that can show colors must have three sub-pixels (red, green and blue color
filters to create each color pixel. These sub pixels are created by applying color filters
that allow only certain wavelengths to pass through them while absorbing the rest. With
a combination of red, blue and green sub pixels of various intensities; a pixel can be
made to appear in many different colors
Through the control and variation of the applied voltage, the intensity of each sub pixel
can range over 256 shades. Combining the sub pixels produces a palette of 16.8
million colors (256 shades of red x 256 shades of green x 256 shades of blue), as
shown below. These color displays take an enormous number of transistors. For
example, a typical laptop computer supports resolutions up to 1,024x768. If we multiply
1,024 columns by 768 rows by 3 sub pixels, we get 2,359,296 transistors etched onto
the glass! If there is a problem with any of these transistors, it creates a "bad pixel" on
the display. Most active matrix displays have a few bad pixels scattered across the
screen. Figure 3 can give you an idea of the RGB sub pixels within each color pixel.
Figure 3
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1.5 LCD Addressing Technology
An Active Matrix LCD is a common type of LCD used in laptops, cameras, LCD
projection panels and LCD TVs that depend upon thin film transistors (TFT). TFTs are
small switching transistors and capacitors arranged in a matrix on a glass substrate as
referenced in figure 4. In order to address a particular pixel the proper row must be
switched on, and then a charge is sent down the correct column. Since all of the other
rows that the column intersects are turned off, only the capacitor at the designated pixel
gets a charge. The capacitor is able to hold the charge until the next refresh cycle.
Pixels within the display are addressed by applying current to a gate line, which
switches the TFT on and allows charge from the source line to flow on to the rear
electrode. This sets up a voltage across the pixel and turns it on.
Figure 4
For example, a high definition LCD TV model such as the TC-22LH1 supports
resolutions up to 1,280x720. If we multiply 1,280 columns by 720 rows by 3 sub pixels,
we get 2,764,800 transistors etched onto the glass! If there is a problem with any of
these transistors, it creates a "bad pixel" on the display. Most active matrix displays
have a few bad pixels scattered across the screen.
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1.6 Backlighting
Backlighting Brightness for Panasonic’s line of LCD TVs is accomplished through the
use of Cold Cathode Fluorescent tubes (CCFT), which is currently the light source of
choice, by a number of leading manufacturers.
1.7 Inverter Power Supply
Pulse width modulation is a very straightforward method for controlling the brightness of
the CCF tube(s). The inverter is turned on and off (using the input or an enable/disable
line) from the Microprocessor Unit (MPU) to control the brightness. The “on” duty cycle
is lengthened to increase the brightness and reduced to decrease the brightness. One
of the major advantages of pulse width modulation is the tube is always fully “on” or fully
“off” and full starting voltage is always applied to the tube(s) (assuming nominal input
voltage. Figure 5 is a simplified diagram of a pulse width modulated DC to AC inverter.
Figure 5
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1.8 High Voltage Power Supply
A CCF tube needs high voltage. The starting voltage is generally over 1,000 volts and
the operating voltage is generally between 200 and 500 volts rms.
Most CCFT DC to AC inverters are tuned switchers designed to produce a specific
voltage, frequency and output current when a designated tube is connected to the
output. The classic current-fed two-transistor inverter has a tuned resonating output,
tuned resonating input and inductive dc input which provides for good power transfer
and high operating efficiency.
Figure 6
T
he type of circuit depicted in Figure 6 inherently produces a pure sine-wave output, but
the voltage and current waveforms are both distorted when they are applied to a CCF
tube, which is a highly nonlinear device. The transition from the starting voltage to the
operating voltage in this circuit is implemented by a small internal series output
capacitor, which serves as the ballast, providing impedance, and allowing prope
current after the tube has been ignited.
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r tube
1.9 Test and Measurement
This is a basic test setup for measuring the output voltages of the inverter circuit. The
output voltage to the tube can be measured with a dual-channel oscilloscope and two
low-capacitance (< 2.5 pf) scope probes. The oscilloscope should be connected
differentially, with the probe grounds connected and floating as depicted in the diagram.
Figure 7 indicates how an oscilloscope can be used for achieving these measurements.
Figure 7
Channel A should be added to the inverse of channel B to produce the complete
waveform on the oscilloscope.
O
utput waveform
Figure 8 is what th
should look like as viewed in the above test
arrangement.
e typical output current waveform
Figure 8
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1.10 Features
ACTIVE SYSTEM CONTROL
Working in tandem with active light control, this technology adjusts the video signal
according to the image contrast, adding greater brightness to bright scenes and more
depth to darker ones, giving you more vivid images and a more powerful viewing
experience.
SUPER DYNAMIC SHARPNESS CONTROL
By analyzing the entire image, minimizing noise in areas of low detail (such as a
cloudless sky), and enhancing areas with greater detail, this circuitry provides a natural,
lifelike picture with outstanding detail.
16:9 ASPECT RATIO
These wide screen TVs have a width-to-height ratio similar to movie theater screens,
providing one with cinema-style entertainment right in your own home. Thus enabling
full-screen viewing of high-definition broadcasts and DVD videos, in a 16:9 format.
PROGRESSIVE SCAN DOUBLER
Displays a full frame of video in 1/60th of a second by de-interlacing the incoming video
signal and progressively scanning the image. This feature helps to reduce the horizontal
scan lines that are often visible in ordinary television images.
3D Y/C DIGITAL COMB FILTER
The 3D Y/C digital comb filter performs field-by-field comparisons of the television
image to accurately separate the color from the black-and-white information. The filter
works to minimize both horizontally and vertically hanging dots, as well as dot crawl.
Component Video Input Jacks
Each of the two components video input jacks consist of a luminance signal and two
separate chrominance signals. These three combined inputs provide video images with
a superior resolution and color accuracy. Panasonic televisions with these component
video inputs can accept either progressive or interlaced signals from a variety of
sources, including DVD players and DTV set-top boxes.
S Video And Composite Input Jacks
Two S video input and Composite connections are available on this model The S video
input jacks consist of a luminance signal and chrominance signal each. These in
addition to the Composite Video input jack provide video signals that are selected via
the A/V switch.
HDMI-DVI Interface
The unit is equipped with a High Definition Multimedia Interface (HDMI), which is
considered to be the first all digital consumer electronics A/V interface that supports
both Digital Video and Audio. DVI currently does not support audio.
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