The procedure described here, will help you repair a Samsung 2008-2013 panel screens, that use gate circuits embodied in glass screen cell (chip on glass - COG). The procedure has a rate of success of 0-100%, depending on your screen panel. You have to accept that sometimes, even the screen panel will work, a thin line may appear aleatory on screen. Also, sometimes, the screen will not respond to any procedure described here.
Repairing the gate problems of Samsung LCD display panels.
A display device includes multiple pairs of field generating electrodes and an electrooptical active layer interposed there between. Generally, one of the pair of field generating electrodes is connected to a switching element to receive an electric signal and the electro-optical active layer converts electric signal into an optical signal to display images.
The display device typically includes a gate driver and a data driver. The gate driver applies to a gate line a gate signal that turns a pixel on and off, and the data driver converts image data into a data voltages and then applies the converted data voltage to a data line.
The gate signals are are processed by the scan driver circuits and amplified by the level shifter to analog signals, which are outputted as the gate pulses for scanning the display panel.
Gate driving circuits can be mounted - (TCP) tape carrier package or printed on glass - (COG) chip on glass. On Samsung panels, gate driving circuits were replaced since 2008-2009 with gate drivers on glass mounted transistors, using ASG technology (Amorphous Silicon Gate).
Each gate line has a block circuit glass mounted transistors called SR, made using ASG technology. The gate driver receives clock signals CKV and CKVB and the start signal STVP, and sequentially apply on voltages to gate lines.
The display area 300 is represented by the resistor Rp and the capacitor Cp. As show below, the gate lines G1-Gn, and the liquid crystal capacitor CIc and storage capacitor
Cst , respectively have the resistance and capacitance, and the sum thereof is represented by one resistor Rp and one capacitor Cp.
The gate voltage output from each line block SR1-SRn is analog transmitted through the gate line corresponding.
The SR blocks are connected between, with glass printed connections, and when a component of one SR block faults, owing to the fact that is on glass, the repair is impossible.
Repairing the gate problems of Samsung LCD display panels.
A display device includes multiple pairs of field generating electrodes and an electrooptical active layer interposed there between. Generally, one of the pair of field generating electrodes is connected to a switching element to receive an electric signal and the electro-optical active layer converts electric signal into an optical signal to display images.
The display device typically includes a gate driver and a data driver. The gate driver applies to a gate line a gate signal that turns a pixel on and off, and the data driver converts image data into a data voltages and then applies the converted data voltage to a data line.
The gate signals are are processed by the scan driver circuits and amplified by the level shifter to analog signals, which are outputted as the gate pulses for scanning the display panel.
Gate driving circuits can be mounted - (TCP) tape carrier package or printed on glass - (COG) chip on glass. On Samsung panels, gate driving circuits were replaced since 2008-2009 with gate drivers on glass mounted transistors, using ASG technology (Amorphous Silicon Gate).
Each gate line has a block circuit glass mounted transistors called SR, made using ASG technology. The gate driver receives clock signals CKV and CKVB and the start signal STVP, and sequentially apply on voltages to gate lines.
The display area 300 is represented by the resistor Rp and the capacitor Cp. As show below, the gate lines G1-Gn, and the liquid crystal capacitor CIc and storage capacitor
Cst , respectively have the resistance and capacitance, and the sum thereof is represented by one resistor Rp and one capacitor Cp.
The gate voltage output from each line block SR1-SRn is analog transmitted through the gate line corresponding.
The SR blocks are connected between, with glass printed connections, and when a component of one SR block faults, owing to the fact that is on glass, the repair is impossible.
However,
with some trickery made on command signals of gate drivers blocks, you can
partially or totally repair the faults.
CKV and phase opposition CKVB signal, and start STVP signal, are synchronizing the gate outputs to screen lines. For a small screen, we will have only one set of signals: CKV, CKVB and STVP For a bigger screen, we will have 2 gate drivers blocks and 2 sets of signals, CKV1, CKVB1, STVP1 and CKV2, CKVB2, STVP2, each of this signals sets will
command a gate driver on down or upper side of the screen.
The fault can be visible on all screen, half of screen, so we need to cut in both signals sets, or one by one, depending on each situation.
On large screen panels, starting with 32 inch, there are gate drivers on both sides of the screen, and we can have 2,3 or 4 sets of signals.
In this case, the command of 4 blocks gate drivers (CKV1.....CKV4, etc) are made in various ways, one way it is as below:
-first gate signal will command upper side of screen odd lines, second gate signal - lower side of screen odd lines, third gate signal will command upper side of screen even lines, fourth gate signal lower side of screen even lines.
A fault screen will display in many ways: -Doubled image on all screen, on vertical, or image stop.
CKV and phase opposition CKVB signal, and start STVP signal, are synchronizing the gate outputs to screen lines. For a small screen, we will have only one set of signals: CKV, CKVB and STVP For a bigger screen, we will have 2 gate drivers blocks and 2 sets of signals, CKV1, CKVB1, STVP1 and CKV2, CKVB2, STVP2, each of this signals sets will
command a gate driver on down or upper side of the screen.
The fault can be visible on all screen, half of screen, so we need to cut in both signals sets, or one by one, depending on each situation.
On large screen panels, starting with 32 inch, there are gate drivers on both sides of the screen, and we can have 2,3 or 4 sets of signals.
In this case, the command of 4 blocks gate drivers (CKV1.....CKV4, etc) are made in various ways, one way it is as below:
-first gate signal will command upper side of screen odd lines, second gate signal - lower side of screen odd lines, third gate signal will command upper side of screen even lines, fourth gate signal lower side of screen even lines.
A fault screen will display in many ways: -Doubled image on all screen, on vertical, or image stop.
-Half
of screen, upper or lower, doubled or static image, the other half will be
correct displayed
-On whole screen are horizontal lines where image is reversed or static.
-a part of the screen is darker, with lines
-vertical flickering image on all screen or upper or lower half of the screen
-in a area of the screen, the image have lines on it.
-on area where image is not right, can also to have a certain color or fail of color.
-On whole screen are horizontal lines where image is reversed or static.
-a part of the screen is darker, with lines
-vertical flickering image on all screen or upper or lower half of the screen
-in a area of the screen, the image have lines on it.
-on area where image is not right, can also to have a certain color or fail of color.
REPAIRING
SAMSUNG SCREENS BY DISCONNECTING GATE DRIVERS SIGNALS.
The
generating circuit for gate drivers, called LEVEL SHIFTER or SCAN DRIVER, can
be mounted on T-CON drivers, on PWB (printed wire board) connected to screen,
or in glass screen.
When level shifter is in glass cell, you cannot disconnect it, but you can try to disconnect the input signal – CPV, STV and OE. This signals will go on both sides of the screen, thru left and right PWB, you can disconnect one side first, check if any improvement, and if not, disconnect other side and re-connect first one.
First of all you have to check where is the LEVER SHIFTER IC, by finding check points CKV CKVB and STVP. Usually the LEVER SHIFTER is on TCON board or on T-CON PWB attached to the screen glass cell.
When you cut CKV, CKVB and STVP signals on printed wire circuit, you have to be sure that the disconnection will be made to screen direction, there are several situations when connection with level shifter is between check points and screen, so cutting the printed wire circuit near this check points to be with no result.
The T-CON processor generates only low voltage gate signals, like CPV, STV and OE, the level shifter circuit is not integrated in t-con processor, is a separate IC.
Sometimes there are 2 or 3 LEVEL SHIFTER IC, like in picture below:
But
latest t-con boards have the same IC for LEVEL SHIFTER and DC-DC source,
especially on small size screens (15-32”)When level shifter is in glass cell, you cannot disconnect it, but you can try to disconnect the input signal – CPV, STV and OE. This signals will go on both sides of the screen, thru left and right PWB, you can disconnect one side first, check if any improvement, and if not, disconnect other side and re-connect first one.
First of all you have to check where is the LEVER SHIFTER IC, by finding check points CKV CKVB and STVP. Usually the LEVER SHIFTER is on TCON board or on T-CON PWB attached to the screen glass cell.
When you cut CKV, CKVB and STVP signals on printed wire circuit, you have to be sure that the disconnection will be made to screen direction, there are several situations when connection with level shifter is between check points and screen, so cutting the printed wire circuit near this check points to be with no result.
The T-CON processor generates only low voltage gate signals, like CPV, STV and OE, the level shifter circuit is not integrated in t-con processor, is a separate IC.
Sometimes there are 2 or 3 LEVEL SHIFTER IC, like in picture below:
Generally,
if screen configuration permits, you have to check the printed wire circuit
from T-COn to both left/right PWBs, in connection to panel for all signals CKV,
CKVB and STVP. The best way to repair is to cut the signals near screen, on left/right
PWB, or left/right connection to screen on PWB (if only one board attached to
screen cell)
Sometimes, cutting some signals only from left or right will solve the image problems but cutting same signals from both right / left connection to screen to generate more errors.
If you have a T-con apart from screen cell, first step is to find which part of the screen is fault. Disconnect left FFC between T-con and left PWB and power the tv. If you have now on right part of the screen a normal image, means that you have a fault in left side of the cell. If still a fault image, re-connect the left FFC and disconnect right FFC between T-con and left PWB and power the tv. If you have now on left part of the screen a normal image, means that you have a fault in right side of the cell.
On some screens, Level Shifter IC have on outputs, some zero ohms resistors, so, you can first remove this resistors and check if any improvements. You should remove on signal groups, for example, when you remove output of CKV2, you have to remove also CKVB2 signal.
Sometimes, you have on left/right PWB, some zero ohms resistors that connect Level Shifter to right/left screen cell. In this case, just remove those resistors for groups that fault. In example below, RM1 connects to screen the STVP signal, RM2 connects to screen CKV1 signal, RM3-CKV2, RM4-CKV3, RM5-CKVB1, RM6-CKVB2, and RM7-CKVB3
Sometimes, cutting some signals only from left or right will solve the image problems but cutting same signals from both right / left connection to screen to generate more errors.
If you have a T-con apart from screen cell, first step is to find which part of the screen is fault. Disconnect left FFC between T-con and left PWB and power the tv. If you have now on right part of the screen a normal image, means that you have a fault in left side of the cell. If still a fault image, re-connect the left FFC and disconnect right FFC between T-con and left PWB and power the tv. If you have now on left part of the screen a normal image, means that you have a fault in right side of the cell.
On some screens, Level Shifter IC have on outputs, some zero ohms resistors, so, you can first remove this resistors and check if any improvements. You should remove on signal groups, for example, when you remove output of CKV2, you have to remove also CKVB2 signal.
Sometimes, you have on left/right PWB, some zero ohms resistors that connect Level Shifter to right/left screen cell. In this case, just remove those resistors for groups that fault. In example below, RM1 connects to screen the STVP signal, RM2 connects to screen CKV1 signal, RM3-CKV2, RM4-CKV3, RM5-CKVB1, RM6-CKVB2, and RM7-CKVB3
As
I explained in previous presentation, the CKV, CKVB and STVP signals scan
between positive voltage VONE and negative voltage VOFFE. Sometimes, a small
raise of VOFFE negative voltage will remove faults of the screen.
STEPS TO REPAIRING A SAMSUNG PANEL
identify the Level Shifter generator, by finding the inputs CPV, OE and STV check points, or finding the outputs CKV1...CKVn, CKVB1...CKVBn, and STVP1...STVPn check points
Check the VONE and VOFF voltages and note the values
First disconnect the CKV1, CKVB1 and STVP signals, after that CKV2, CKVB2, and so on.
disconnections will be made so the wires from screen panel to be “on air”
when disconnect the printed wire board near screen entrance, by cutting the printed circuit, you have to be sure that you will be able to solder this wires, so the cut has to be made with some distance from data driver flexible circuit.
First disconnect, CKV1 and CKVB1- if image still have thin lines, just strap the wires coming from screen panel CKV1 and CKVB1 with a thin wire.
After connecting CKV1 and CKVB1 with a thin wire, try also to ground this 2 points, or try to connect to VOFF.
If no improvements, try to disconnect CKV2 and CKVB2 (with STVP disconnected) and make same steps as for CKV1 and CKVB1 (3,6 and 3.7)
If we have also CKV3, CKVB3 and CKV4 and CKVB4, make the same procedure as CKV1 and CKVB1
identify the Level Shifter generator, by finding the inputs CPV, OE and STV check points, or finding the outputs CKV1...CKVn, CKVB1...CKVBn, and STVP1...STVPn check points
Check the VONE and VOFF voltages and note the values
First disconnect the CKV1, CKVB1 and STVP signals, after that CKV2, CKVB2, and so on.
disconnections will be made so the wires from screen panel to be “on air”
when disconnect the printed wire board near screen entrance, by cutting the printed circuit, you have to be sure that you will be able to solder this wires, so the cut has to be made with some distance from data driver flexible circuit.
First disconnect, CKV1 and CKVB1- if image still have thin lines, just strap the wires coming from screen panel CKV1 and CKVB1 with a thin wire.
After connecting CKV1 and CKVB1 with a thin wire, try also to ground this 2 points, or try to connect to VOFF.
If no improvements, try to disconnect CKV2 and CKVB2 (with STVP disconnected) and make same steps as for CKV1 and CKVB1 (3,6 and 3.7)
If we have also CKV3, CKVB3 and CKV4 and CKVB4, make the same procedure as CKV1 and CKVB1
If, for example, by disconnecting CKV3 and
CKVB3 we have a normal screen display, re-connect the former signals to panel
screen, one by one in pairs (CKV1 and CKVB1, and so on)
It is possible that, sometimes, only by disconnecting pair 1 and 4 to have a normal screen, but by disconnecting all 4 pairs to have a fault image
Sometimes, even the image is correct displayed, you'll have a thin line in the area where gain glass circuit is defective - this cannot be repairable. You have to advice the client about this, and ask him to put in balance the final result of this procedure against the cost of a new panel screen.
It is possible that, sometimes, only by disconnecting pair 1 and 4 to have a normal screen, but by disconnecting all 4 pairs to have a fault image
Sometimes, even the image is correct displayed, you'll have a thin line in the area where gain glass circuit is defective - this cannot be repairable. You have to advice the client about this, and ask him to put in balance the final result of this procedure against the cost of a new panel screen.
