Sunday, November 08, 2015


PANASONIC LED TV TC-L42U25 - TC-L37U22 - TC-L32U22 - TC-L37X2 - TC-L32X2 - TC-L22X2 - TC-L37C22 - TC-L32C22 




When the TV is plugged in, AC voltage is applied to the standby circuit of the power supply circuit to produce STB5V. The STB 5V is provided to the A board via pin 1 of connector P2. The STB 5V enters the application specific integrated circuit (ASIC), IC4700, for conversion to STB3.3V. The STB3.3V is applied to IC8001 to energize and prepare the internal microprocessor for program execution. The 3.3V from the voltage regulator is also applied to the remote control receiver and the power LED on the K board through Pin 3 of connector A10. If the STB5V is missing, the TV is dead (No power)

When the power button of the TV or remote control is pressed, The MPU (IC8001) of the A board outputs the TV_SUB_ON command to turn on the transistors Q4770 and Q4771 which provide STB5V to the power relay. The STB5V enters the power supply board via pin 11 of connector P2. The TV_SUB_ON command is also provided to the power supply to activate a circuit that provides a ground connection to the relay. When the relay is closed, the switched mode supply goes in operation to create the Sound15V, and DTV12V. The DTV12V is regulated to other voltages to power the A-Board.
Caution: All boards in the unit are to be exchanged only.

After sending TV SUB On command, F15V and Sound 15V are supplied to A board. The F15V source also known as the DTV12V is supplied to DC/DC converters, IC5608, IC5606, IC5610 and Q5412. Provided by IC8001, the panel VCC-ON command turns on IC4800 to produce 13.7V and 2.5V for the operation of the TCON circuit located inside the LCD panel. On the other hand, the F15V enters IC5608 for conversion to SUB5V. The F15V is also applied to IC5606 for conversion to SUB1.8V. IC5610 also converts the F15V to SUB1.2V. The sub-voltages are mainly used to power the A-Board. They are all monitored by the IC4700 and subsequently IC8001 for their presence. If any of the sub-voltages is missing, the MPU shuts down the TV and the power LED blinks 3 times. IC5605 and IC5013 convert SUB 5V to SUB 3.3V. When IC8001 is satisfied of the presence of all the monitored sub-voltages, it provides the Backlight_On command to turn on the inverter (Power supply for the backlights). This command enters the P-Board via pin 13 of connector P2. The output of the inverter is in the 2.3KVp-p range for a TC-L37X2 panel.
The SYSTEM MPU on the A board outputs the “TV SUB ON” command (3.2V) when the power is turned on. This command is used to turn on the circuit in the power supply that generates F15V and Sound 15V. F15V is provided to the A board to generate the sub-voltages used by the signal process circuit. The outputs of the sub-voltages 5V, 1.8V and 1.2V are confirmed by ASIC IC4700.
Backlight ON(2)
After receiving SUB3.3V, 1.8V, 1.2V, “Backlight ON” command is applied to the P board power supply from Nile-TCON IC8001 to turn on the P board circuits to start backlight circuit.
Panel STB ON / VCC ON(3)
On the other hand, IC8001 starts the DC/DC converter Q5412 to supply 12V to TCON board.


The INV_ON/OFF command (high) of the MPU, IC8001 of the A board, enters the P-Board to turn on the inverter circuit. The inverter circuit produces AC voltages that power the backlight fluorescent lamps . The output of the inverter, approximately 2Kvp-p is provided to the LCD panel via the connectors P5, P6, P7 and P8. To avoid catastrophic failures, when the inverter circuit is defective, the INV_SOS command is output to IC8001 to trigger the shutdown of the TV. The power LED blinks one time. The same operation takes place when there is an impedance mismatch between the Panel and the inverter. IC7800 is the controller. IC7801 is the oscillator that provides the switching signals to the transistors Q7801 through Q7804. The backlights are manipulated (dimmed) by the control signal INV_PWM coming from the main board Via pin 12 of the connector P2.

The inverter receives 174V from the SMPS. The 174V source is provided to the panel to power the LED. The Backlight_On command from pin 13 of connector P2 starts the inverter drive signals. The inverter control signal, PWM, is delivered by the TCON board at pin 15 of connector P2 to control the brightness of the LEDs. The inverter is responsible for controlling the amount of current passing through the LEDs. To avoid  catastrophic failures, when the inverter circuit is defective, the BACKLIGHT_SOS command is output to IC8001 to trigger the shutdown of the TV. The power LED blinks one time.

The main function of the A board is to select and process one of the incoming video signals. Video inputs 1 and 2, Component Video Input, HDMI inputs 1, 2 and 3, JPEG data from the SD card slot, and the composite video output of the tuner are all connected to IC8001 for selection. The video input signal can be in any of the three formats: Video, Y/C, YPbPr . All analog signals that enter IC8001 undergo digital to analog conversion. When the signal source signal is composite, a comb filter separates the video signal into Y and C (luminance and chrominance) signals. S-Video, which is already Y/C separated, simply passes through the comb filter. The signal is then converted to RGB data. At the completion of this process, the format of the composite or S-Video signal is now the same as a digital 480i component signal. If the incoming video is in the 480p, 720P, 1080i, and 1080p format, the Y, Pb, and Pr signals undergo A/D (analog to digital) conversion only. Digital television reception of the tuner is output in the form of an IF (Intermediate Frequency) signal . The transport stream from the tuner enters the VSB I/F (Interface) section of IC8001 where the video signal is extracted and converted to RGB data. The output is provided to the Video Input I/F for selection. The JPEG data of the SD card enters the JPEG I/F section of IC8001 for conversion into RGB data and output to the Video Input I/F circuit. The video input interface outputs the selected picture data to the video process circuit. The Video Process section of the IC performs all picture control operations such as brightness, contrast, color, tint, etc. On Screen Display data such as channel numbers, Digital TV closed caption, and picture adjustments are mixed with the video data. The RGB data is then converted to dual 14 bit LVDS (Low Voltage Differential Signaling) and output to the LCD panel. IC8001 handles all video applications. It serves as the controller that monitors all operations of the TV section of the unit.