HOW TO DIAGNOSE A FAILED T'CON BOARD - HOW TO REPLACE A T'CON BOARD
Sony T'Con board
Samsung T'Con board
What is the T-CON Function? The T-CON (TFT Controller) is responsible for; 1. Driving the TFT panel. This is usually accomplished by two LVDS type cables between the T-CON and the th Panel. P l The Th panel l cell ll structure t t i is broken b k into i t Vertical V ti l columns l and d H Horizontal i t l rows. • Horizontal Resolution: On a panel with a resolution of 1920 X 1080 we must have 1920 X 3 columns, because a pixel is comprised on a Red, Green and Blue cell. So there will be 5760 individual cells in rows across the screen. To turn these cells on and off, the panel will use vertical address lines or electrodes driven by y a small board located inside the panel. p In this way y we can turn the colors on and off accordingly to recreate the correct colors required to recreate the image. • Vertical Resolution: On a panel with a resolution of 1920 X 1080 there will be 1080 horizontal rows of cells running across the panel. These rows are being driven by a small board inside the panel. By 2.addressing a particular cell via the vertical columns and turning on a row of cells, only the cells being address by the vertical electrodes will be activated. activated The number of horizontal rows determine the panels Vertical resolution. TFT: Each cell has is driven by a thin film transistor called (TFT) and a capacitor. When that cells is addressed (turned on) the capacitor will charge and will remain charged until the next refresh cycle. Generally speaking, when the cell has no power applied, it blocks the light from passing through, when it turns on, dependant upon how long it is on, allows more or less light to pass. In this way we can control the brightness level being output by that cell. Panel Voltages: The T-CON is responsible for developing panel voltages. These voltage will vary dependant upon the type of panel utilized. utilized We generally state there will be 4 voltages that are always being delivered to the panel, -5V, 3.3V, 16V and 26V. However, there may be more according to the type of panel being used. Backlights: Since the Liquid crystal panel does not generate any light of its own, there must be a light source behind the panel. This light source is called the “Backlights” called B\L here after. The B\L can be either florescent (EEFL or CCFL) or they can be LED. The T-CON is not responsible for turning on the B\L.
T-CON Shield Purpose and Key PointThe T-CON shield may serve two functions. 1) They prevent RF radiation, either in or out. 2) They Th work k as a h heat t di dissipation i ti shield. hi ld Here are some key points to remember when removing the shield; o Many M of f th the shields hi ld h have a piece i of f material t i l that is used to transfer heat from a component on the board to the shield. This material is called “Chocolate”. Look for it when removing the shield. Make sure to return it to the correct location when replacing the shield. In the example on the right, the two pieces of chocolate are protecting the DC-to-DC converter coils in the lower right hand corner.
Understanding the LVDS Cable.
The LVDS (Low Voltage Differential Signal) Cable in a LCD TV is responsible for two primary jobs. 1. VIDEO and TIMING SIGNALS: To deliver video signals g that have been p processed into a positive and a negative going pair of signals. These pair of signals are sent is groups which equal the resolution characteristics of the panel. As an example if the panel is a HD panel, the differential pair will be 10 lines carrying positive and negative going video data. And there will be two line carrying positive and negative going clock signals. If the panel is a full HD panel, it will have double the amount of lines lines. The positive going signals will be designated on the schematic with the suffix of (P or +) and the negative going lines will be designated as (N or -). If you take one pare of video signals and look at them on a scope, they will be and exact mirror of each other. One going positive and one going negative. By using a differential pair, the circuitry can isolate and remove the noise on the line by addition and it can extract the actual signal by subtraction which will double the signal level. 2. T-CON VOLTAGE: The T-CON board needs voltage to operate, the LVDS cable will deliver the T-CON’s operational voltage. If the th LVDS cable bl i is suspected t d of fh having i a problem, bl most t often ft i is can b be seen visually. i ll L Look k for f the th cable being bent which cause the internal paths to be broken. The cable can be cut, or cracked or physically damaged in some way. The other problem that the LVDS cable can have is the continuity contacts that are on the side that goes into the connector can separate from the cable itself. This can only y be seen by y unlocking g the cable connector and removing g the cable. Then flipping pp g the cable over so the contacts points can be seen. See if they are separated from the cable. They could be curled up or even bent over and pressed onto another line causing a short. One other thing to look for is the cable being incorrectly inserted into the connector, (improperly seated). When the LVDS cable is causing a problem, the symptom can be many. Lines in the picture, portions blocked bl k d out, t every other th li line missing, i i noise i patters tt on the th screen, missing i i 12V t to the th T-CON T CON causing i a black or no picture symptom, etc... It can even shut the TV down if the 12V is shorted.DIAGNOSING A FAILED T'CON BOARD
All video inputs received by the video process circuits are
handled on a frame-by-frame basis. The
video frames are converted and scaled to 8 to 10 bit RGB information. It is virtually impossible for the video
process circuit to cause a problem on a specific area of the screen. Failures on this board usually appear as
distortions, color level shifts, video level shifts or noise that involves the
entire picture. The T’Con can generate
symptoms that appear to be video process related, but the video process circuit
cannot produce the symptoms of a failed T’Con board circuit.
T'CON FAILURES
Failures in the timing control circuits of the T’Con can
produce symptoms of absolutely no video or generate lines and patterns that
usually cover all or a substantial part of the screen. Determining if the T’Con is the cause of a
‘No Video’ condition is a bit more difficult since there are no indications on
the screen to analyze. Many of the Sony TV models ove the last few years will
detect a T’Con that has completely failed.
The communications data between the video process circuits and the T;Con
will cease to communicate, iif the T’Con fails completely. This will cause the TV to shut down and
display a diagnostic code, indicating a failure of the T’Con. Not all chassis designs have this feature
and it is not found on older models.
The typical scenario when this failure arises is for the technician to
bring a video process board to the repair location. It is usually safe to assume that the problem lies on the T’Con
board, if the replacement video board dos not give a solution to the problem
since it is highly unlikely that a replacement board with the same failure was
received. One trick to check most
T’Cons for functionality is to loosen the LVDS connector at the T’Con while
unit is turned ON. Handle the LVDS
connector with care and be certain to fully release the lock tabs. Gently rock the cable in and out of the
connector while observing the screen for any response. Depending on the chassis, the symptoms of
the screen ma be gentle white flashes, intermittent coloured lines, or a screen full of random patterns. The idea at
this point is to provoke some kind of response on the screen. Another helpful procedure is to rapidly heat
and/cool the T’Con with a hot air devices or circuit coolant and watch for
patterns appear on the screen.
LVDS cable failures
Although the problem with LVDS cable or connectors can
generate symptoms of T’Con failures this usually tends to be intermittent and wiggling
of the connectors will usually provoke
a change in the symptom on the screen.
LVDS cable and connectors have became rather robust over the past few
years. Technicians who damage them
cause most problems and this is generally quite oblivious upon close
examination.
LVDS CABLE
LCD panel failures
Some LCD panel failures could possibly mistaken for T’Con
board issues. Other than damage to the
LCD glass, most panel failures are isolated to a particular area of the
screen. Since the T’Con disperses the
pixel data to groups of line and column dirve IC’s situated on the outer edges
of the panel, it is unlikely that more than one of these IC’s would fail at the
same time. Multiple columns of struck
on or stuck off pixels are therefore, more likely to be the fault of the T’Con
circuits. The same applies to a single
row of lit or unlit pixels. The T’Con
simply cannot cut out a single line of information.
In many instances, replacement of the T’Con board will be
relatively straight forward. In some
case, the other boards may have to be loosened or removed to allow access to
the mounting screws and clearance to remove the T’Con board. The issue of most concern is keeping track
of the heat transfer pads, stand offs and insulators. The T’Con is heavily shielded and it si ease to have one or more
of these components accidentally fall out of the assembly when removing. T’Con assemblies that use multiple heat
transfer pads must be removed slowly and every attempt must be made to keep the
shield and circuit board together as they are removed from the unit. Check for any service bulletins pertaining
to the model and panel design that contain the subject lie of ‘T’Con heat
transfer pad locations’ for pictures to show the proper location of these
components. This site itself has
covered disassembly procedure to some model LCD TVs, here. Pull up older posts here, or see the site in
Timeslide option, which can be accessed by the drop down at the top left side of the display
window. It will make search the easily.
Remove the screw from the LVDS cable ground strap so the
cable can be moved away. Unplug the
connector to inverter board and remove harness from the retainer. Remove all screws securing the board
sub-chassis to the panel. Pull the top
of the board toward you and downward to allow access to the bottom screws securing
T’Con. The position of screws, and
disassembly method may vary set to set.
Carefully unpeel the conductive tape from the top bracket
taking care not to tear them. Leave the
tape attacked to the T’Con shield.
Remove the top bracket covering the gate and source driver
components. This will allow access to
the upper flat cable connectors, if any.
Carefully lift the locking tabs securing the flat cables. Leave the fat cables attached to the T’Con
and shield ass;y. the T’Con board will
have an insulating pad between it and the LCD panel that will cause the board
to stick. Not much effort is required
to release it. The goal at this point
is to remove the board and shield together so as to avoid dropping heat
transfer pads and insulators located between the front of the board and the shield. If successful, Both components should stay
together as insulated. Note the spaces
mounted on the backside of the board.
These will need to be transferred to the replacement board. Lift the circuit board upward slowly while
observing the location of the heat transfer and insulating pads. In most cases the heat transfer pad will
remain attached to their appropriate ICs and the insulating pads will be struck
to the shield. If anything falls off,
use the instruction to return them to their proper position. Transfer all heat and insulating pads along
with the flat cables to the replacement board.
Once the components have been transferred to the front of the circuit
board, attach the shield and flip the assembly. Transfer any spacers or insulating pads to the replacement
bard. Temporarily secure the T’Con
board to the shield with electrical tape.
This helps in preventing movements of the circuit bard while installing
the assembly back into the LCD panel.
Once the T’Con ass’y is secured to the panel, insert and lock the flat
cables. Plug in all connectors and
secure the board sub chassis. Do not
forget about the wire harness that was removed from its retainer.