TCON
Troubleshooting and Replacement
In the relatively small
percentage of units that experienced a failure of the TCON board, replacement
of the entire LCD panel was mandatory. This is not only costly from a warranty
standpoint but it also makes it near impossible to justify an out-of-warranty
repair since the replacement LCD panel can easily cost 2/3 or more of the price
of the entire television.
The reason why TCON assemblies have not been available in the past was due to the large amount of correction data stored within NVM data points located on the board. Tolerance issues during the manufacture of the LCD panels required white balance, gamma, and uniformity corrections to compensate for these inherent production issues. There are other items for correct panel operation but the above mentioned items are the most critical.
Over the years, panel tolerances have improved dramatically and variances in uniformity have been reduced to the point where a TCON loaded with average data results in a satisfactory picture when installed as a replacement on a panel. Most Sony television models also have white balance data located on the video process board. Although
the TCON is loaded with data to properly white balance the panel, the ability to adjust white balance from the B boards is present to compensate for shifts in white balancing due to panel ageing and this mainly involves colour balance shifting of the fluorescent backlight lamps which tend to shift towards the magenta spectrum as they age.
The main issue with previous LCD panel designs was the uniformity adjustment data. Due to variances across the LCD panel it was impossible to achieve even white balance across the screen. For this reason, small zones across and down the LCD panel required individual white balance compensation. Without this correction the
picture would have “blotches” of different colour in sections of the screen. Better tolerances during manufacturing have reduced the reliance on this uniformity data and allows for the replacement of TCON boards with satisfactory results.
not all LCD panels will have a TCON board available. This will mainly be determined by availability of components from the LCD panel vendor along with decisions by Sony based on sales quantity and failure history of the TCON assemblies. Most technicians have experienced the use of the LCD panel replacement manual. This manual was created to proper identify the type of LCD panel installed in a unit based on its serial number since some units changed to a different type of LCD panel during the manufacturing
production. The plan is to use this document to also provide TCON information and whether one is available and, if available, which TCON is the proper replacement part for that particular panel.
The reason why TCON assemblies have not been available in the past was due to the large amount of correction data stored within NVM data points located on the board. Tolerance issues during the manufacture of the LCD panels required white balance, gamma, and uniformity corrections to compensate for these inherent production issues. There are other items for correct panel operation but the above mentioned items are the most critical.
Over the years, panel tolerances have improved dramatically and variances in uniformity have been reduced to the point where a TCON loaded with average data results in a satisfactory picture when installed as a replacement on a panel. Most Sony television models also have white balance data located on the video process board. Although
the TCON is loaded with data to properly white balance the panel, the ability to adjust white balance from the B boards is present to compensate for shifts in white balancing due to panel ageing and this mainly involves colour balance shifting of the fluorescent backlight lamps which tend to shift towards the magenta spectrum as they age.
The main issue with previous LCD panel designs was the uniformity adjustment data. Due to variances across the LCD panel it was impossible to achieve even white balance across the screen. For this reason, small zones across and down the LCD panel required individual white balance compensation. Without this correction the
picture would have “blotches” of different colour in sections of the screen. Better tolerances during manufacturing have reduced the reliance on this uniformity data and allows for the replacement of TCON boards with satisfactory results.
not all LCD panels will have a TCON board available. This will mainly be determined by availability of components from the LCD panel vendor along with decisions by Sony based on sales quantity and failure history of the TCON assemblies. Most technicians have experienced the use of the LCD panel replacement manual. This manual was created to proper identify the type of LCD panel installed in a unit based on its serial number since some units changed to a different type of LCD panel during the manufacturing
production. The plan is to use this document to also provide TCON information and whether one is available and, if available, which TCON is the proper replacement part for that particular panel.
LCD panels have steadily evolved
over the last several years. New designs of the physical structure of the LCD crystals
have greatly improved the contrast ratio and viewing angle. Quicker response
times and increased refresh rates have helped to reduce the motion “smear”
associated with LCD displays. Back-lighting design has also aided in producing a
picture with colour temperatures to make the images as true as possible. With
all these design improvements, one aspect of the LCD panel remains relatively
the same: Processing of the video signal.
A typical LCD panel and the associated video processing circuits as found in the WAX3 chassis. The various formats and resolutions of video signals are processed on the BU1 board. All video signals exit the video processor in the native resolution of the LCD panel. In this design, the resolution is for a 1280 by 768 at 60HZ refresh rate panel. 48 horizontal lines are discarded to match up to the 720p resolution of the ATSC specifications so the video will exit as 720p.
The LCD panel used in this model processes 8-bit RGB video data. Before the video information can be sent to the TCON board it must be converted to a format that allows for practical and noise-free transmission. The large number of parallel lines to transmit the 8-bit RGB data would need to be sent on differential lines for noise reduction. This would require 48 lines just for the video. The TCON circuit also requires B+, ground connections, a communications bus, sync, and a clocking line transmitted deferentially so we can see that up to 100 lines would be required. The practical way to transmit this information is to convert the parallel video data to a serial stream and this is accomplished by the Low-Voltage Differential Signalling (LVDS) transmitter.
The LVDS transmitter contains a circuit to serialise the parallel data. The parallel video information along with sync and clocking data are transmitted via twisted line pairs. Depending on the logic level, current is sent along one or the other of the twisted pair of wires. The receiving end of the wires is loaded with a resistor (usually around 100 to 120 ohms). The receiver detects the polarity of the voltage drop across the resistor to determine the logic level. The current level swings in the wire are about 3ma with a voltage differential of around 350mv.
This allows for transmission of the video signal with minimal EMI.
The LVDS receiver on the TCON board converts the serialised data back to parallel. This data is processed by the timing control IC to allocate the RGB data into serial streams for processing by the LCD panel. The LCD panel contains shift registers and drivers for all of the rows and columns of pixels on the panel. The drivers are mounted on flexible circuit boards and bonded to the top and side of the panel. Without this arrangement the TCON would require an IC and connectors to transmit on 4,560 lines. All of this is accomplished by the TCON board. The term “TCON” is short for Timing Control. Other LCD panel manufacturers may have a different name for this particular circuit but the term used by Sony will always be TCON.
A typical LCD panel and the associated video processing circuits as found in the WAX3 chassis. The various formats and resolutions of video signals are processed on the BU1 board. All video signals exit the video processor in the native resolution of the LCD panel. In this design, the resolution is for a 1280 by 768 at 60HZ refresh rate panel. 48 horizontal lines are discarded to match up to the 720p resolution of the ATSC specifications so the video will exit as 720p.
The LCD panel used in this model processes 8-bit RGB video data. Before the video information can be sent to the TCON board it must be converted to a format that allows for practical and noise-free transmission. The large number of parallel lines to transmit the 8-bit RGB data would need to be sent on differential lines for noise reduction. This would require 48 lines just for the video. The TCON circuit also requires B+, ground connections, a communications bus, sync, and a clocking line transmitted deferentially so we can see that up to 100 lines would be required. The practical way to transmit this information is to convert the parallel video data to a serial stream and this is accomplished by the Low-Voltage Differential Signalling (LVDS) transmitter.
The LVDS transmitter contains a circuit to serialise the parallel data. The parallel video information along with sync and clocking data are transmitted via twisted line pairs. Depending on the logic level, current is sent along one or the other of the twisted pair of wires. The receiving end of the wires is loaded with a resistor (usually around 100 to 120 ohms). The receiver detects the polarity of the voltage drop across the resistor to determine the logic level. The current level swings in the wire are about 3ma with a voltage differential of around 350mv.
This allows for transmission of the video signal with minimal EMI.
The LVDS receiver on the TCON board converts the serialised data back to parallel. This data is processed by the timing control IC to allocate the RGB data into serial streams for processing by the LCD panel. The LCD panel contains shift registers and drivers for all of the rows and columns of pixels on the panel. The drivers are mounted on flexible circuit boards and bonded to the top and side of the panel. Without this arrangement the TCON would require an IC and connectors to transmit on 4,560 lines. All of this is accomplished by the TCON board. The term “TCON” is short for Timing Control. Other LCD panel manufacturers may have a different name for this particular circuit but the term used by Sony will always be TCON.
Diagnosing
a Failed TCON
In order for this concept to move forward successfully, it is important that the service industry be able to properly identify the symptoms of TCON issues to avoid unnecessary service calls and repair costs. Accurate analysis of TCON failures will reduce costs significantly (both in parts costs and time) when warranty repairs are involved and will reduce the number of COD repairs that are lost.
A good approach when determining a TCON failure is a good understanding of which symptoms ARE NOT caused by the TCON. Examples are as follows:
Video Process Failures: 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 or 10-bit RGB information. It is virtually impossible for the video process circuits 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 TCON can generate symptoms that appear to be video process related but the video process circuits cannot produce the symptoms of a failed TCON circuit.
LVDS Cable Failures: Although problems with the LVDS cable or connectors can generate symptoms of TCON failures this usually tends to be intermittent and wiggling of the connectors will usually provoke a change in the symptom on the screen. LVDS cables and connectors have become rather robust over the past few years and most problems are caused by technicians who damage them and this is generally quite obvious upon close examination.
LCD Panel Failures: Some LCD panel failures could possibly be mistaken for TCON issues. Other than damage to the LCD glass, most panel failures are isolated to a particular area of the screen. Since the TCON disperses the pixel data to groups of line and column drive 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 stuck on or stuck off pixels are, therefore, more likely to be the fault of the TCON circuits. The same applies to a single row of lit or unlit pixels.
The TCON simply cannot cut out a single line of information. Figure 2 illustrates some typical symptoms of failures that are caused by the LCD panel.
In order for this concept to move forward successfully, it is important that the service industry be able to properly identify the symptoms of TCON issues to avoid unnecessary service calls and repair costs. Accurate analysis of TCON failures will reduce costs significantly (both in parts costs and time) when warranty repairs are involved and will reduce the number of COD repairs that are lost.
A good approach when determining a TCON failure is a good understanding of which symptoms ARE NOT caused by the TCON. Examples are as follows:
Video Process Failures: 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 or 10-bit RGB information. It is virtually impossible for the video process circuits 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 TCON can generate symptoms that appear to be video process related but the video process circuits cannot produce the symptoms of a failed TCON circuit.
LVDS Cable Failures: Although problems with the LVDS cable or connectors can generate symptoms of TCON failures this usually tends to be intermittent and wiggling of the connectors will usually provoke a change in the symptom on the screen. LVDS cables and connectors have become rather robust over the past few years and most problems are caused by technicians who damage them and this is generally quite obvious upon close examination.
LCD Panel Failures: Some LCD panel failures could possibly be mistaken for TCON issues. Other than damage to the LCD glass, most panel failures are isolated to a particular area of the screen. Since the TCON disperses the pixel data to groups of line and column drive 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 stuck on or stuck off pixels are, therefore, more likely to be the fault of the TCON circuits. The same applies to a single row of lit or unlit pixels.
The TCON simply cannot cut out a single line of information. Figure 2 illustrates some typical symptoms of failures that are caused by the LCD panel.
Failures in the timing control
circuits of the TCON 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 TCON is the cause of a “no video” condition is a bit more
difficult since there are no indications on the screen to analyse.
Troubleshooting a “dead” TCON
Many of the Sony television models over the last few years will detect a TCON that has completely failed. The communications data between the video process circuits and the TCON will cease to communicate if the TCON fails completely. This will cause the television to shut down and display a diagnostics code indicating a failure of the TCON. 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 TCON board if the replacement video board does not remedy the problem since it is highly unlikely that a replacement board with the same failure was received.
One trick to check most TCONS for functionality is to loosen the LVDS connector at the TCON (as shown In Figure) while the 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 may 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. TCON boards that have failed will not usually generate any type of response on the screen.
Another helpful procedure is to rapidly heat and/or cool the TCON with hot air devices or circuit coolant and watch for patterns to appear on the screen.
Troubleshooting a “dead” TCON
Many of the Sony television models over the last few years will detect a TCON that has completely failed. The communications data between the video process circuits and the TCON will cease to communicate if the TCON fails completely. This will cause the television to shut down and display a diagnostics code indicating a failure of the TCON. 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 TCON board if the replacement video board does not remedy the problem since it is highly unlikely that a replacement board with the same failure was received.
One trick to check most TCONS for functionality is to loosen the LVDS connector at the TCON (as shown In Figure) while the 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 may 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. TCON boards that have failed will not usually generate any type of response on the screen.
Another helpful procedure is to rapidly heat and/or cool the TCON with hot air devices or circuit coolant and watch for patterns to appear on the screen.
2 examples of a loss of control
data to the drive IC’s. In the first example, an entire group of column drivers
has lost the data stream for red. The second example involves the complete loss
of drive data for all RGB information to the right side of the screen. This is
sometimes caused by the flat cable connecting the TCON to the LCD panel coming
loose. The area of missing video can be dark or completely white depending on the
panel design.
Other TCON failures that have been
encountered in the field. The idea is to get a grasp of the concept of TCON
induced failures to avoid unnecessary parts replacement.
TCON
Replacement
In many instances, replacement of the TCON board will be relatively straightforward. In some cases, other boards may have to be loosened or removed to allow access to the mounting screws and clearance to remove the TCON. The issue of most concern is keeping track of the heat transfer pads, standoffs and insulators. The TCON is heavily shielded and it is easy to have one or more of these components accidentally fall out of the assembly when removing.
TCON 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 line of “TCON heat transfer pad locations” for
pictures to show the proper location of these components.
The removal of the TCON board from a KDL40XBR6 is demonstrated. It serves as an excellent example since it requires the partial removal of the power supply board along with containing 6 heat transfer pads, 3 insulating pads, and 5 insulated standoff pads.
Unplug the LVDS connector from the TCON. Remove the screw from the LVDS cable ground strap so the cable can be moved away. Unplug CN6600 from the inverter board and remove the harness from the retainer as shown. Remove the 6 black machine screws securing the g board sub-chassis to the panel.
Pull the top of the G board towards you and downward to allow access to the bottom screws securing the TCON.
Carefully un-peel the conductive
tape from the top bracket taking care not to tear them.In many instances, replacement of the TCON board will be relatively straightforward. In some cases, other boards may have to be loosened or removed to allow access to the mounting screws and clearance to remove the TCON. The issue of most concern is keeping track of the heat transfer pads, standoffs and insulators. The TCON is heavily shielded and it is easy to have one or more of these components accidentally fall out of the assembly when removing.
TCON 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 line of “TCON heat transfer pad locations” for
pictures to show the proper location of these components.
The removal of the TCON board from a KDL40XBR6 is demonstrated. It serves as an excellent example since it requires the partial removal of the power supply board along with containing 6 heat transfer pads, 3 insulating pads, and 5 insulated standoff pads.
Unplug the LVDS connector from the TCON. Remove the screw from the LVDS cable ground strap so the cable can be moved away. Unplug CN6600 from the inverter board and remove the harness from the retainer as shown. Remove the 6 black machine screws securing the g board sub-chassis to the panel.
Pull the top of the G board towards you and downward to allow access to the bottom screws securing the TCON.
Leave the tape attached to the TCON shield. Remove the top bracket covering the
gate and source driver components. This will allow access to the upper flat
cable connectors.
Lift the locking tabs securing
the flat cables. Leave the flat cables attached to the TCON. Remove the 8
silver machine screws securing the TCON and shield assembly. The TCON board has
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 illustrated. Note the spacers mounted on the back side
of the board. These will need to be transferred to the replacement board. In
Figure the insulating pad can be observed sticking to the chassis.
The assembly is laid with the
shield down on the work surface. Lift the circuit board upward slowly while
observing the location of the heat transfer and insulating pads. In most cases
the heat transfer pads will remain attached to their appropriate IC’s and the
insulating pads will be stuck to the shield. If anything falls off, use the
illustration 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
over as shown.
Transfer any spacers or insulation pads to the replacement board.
Transfer any spacers or insulation pads to the replacement board.
Once the components have been
transferred to the front of the circuit board, attach the shield and flip the assembly
over as shown.
Transfer any spacers or insulation pads to the replacement board.
Transfer any spacers or insulation pads to the replacement board.
Temporarily secure the TCON board
to the shield with electrical tape as shown in Figure. This helps in preventing
movement of the circuit board while installing the assembly back onto the LCD
panel.
Once the TCON assembly is secured to the panel, insert and lock the flat cables. Plug in all connectors and secure the G board sub-chassis. Don’t forget about the wire harness that was removed from its retainer.
Once the TCON assembly is secured to the panel, insert and lock the flat cables. Plug in all connectors and secure the G board sub-chassis. Don’t forget about the wire harness that was removed from its retainer.
