LS55A31 – Haier LCD TV – repair help – Power board circuit diagram and descriptions, firmware update

Model: LS55A31 (DH1TV0A0801), 0907732277 RTD2995 square board (no template interface), Power: 0094065514A

TD2995D is an LCD TV solution with support for domestic specifications. It is applied to 26 inches or more (including 26 inches).

The product. Equipped with a liquid crystal display with interface type Vby1. The resolution of the supported screen can reach upto 4K*2K.

The movement module uses REALTEK's video and audio decoding chip RTD2995D  uses NXP's silicon tuner core.

The TDA18275, the system performance is stable, the picture quality is fine.

The video part of the movement module supports 1 channel AV signal input (multiplexed with YPbPr Y signal), 1 channel Video signal output, 1 way YPbPr video signal, 2 way HDMI, 1 way network port, 1 way USB2.0, 1 way USB3.0, all the way TF card, built-in WIFI.

Uses TI's 54628 to power the CPU, the core voltage output is 1.2V, the current is about 4.8A, close to 5A, so choose 6A DC/DC.

+12V Normal to +5V Standby and +5V Normal

This circuit consists of a PWM switching power supply consisting of U17-TI54328 peripheral components. U17 is the switching control device and L7 is the storage inductor. Output 5V  is fed to the control circuit inside the U17(2) pin via R84, R79 partial pressure feedback for PWM control to ensure 5V voltage regulation.

When the switch  is closed, the current of the 5V power supply flows through the self-inductance of L7, and the current gradually rises and is stored as magnetic energy. Self-induced potential.

The direction is left positive and right negative flow through L7, the current charges the capacitor, the voltage across the capacitor gradually rises, and supplies power to the load, when the voltage across the capacitor exceeds

 5V, it will send the feedback voltage of FB terminal of (2) pin of U17 to make the internal switch of TI54328 cut off. At this time, the self-inductance potential of L7 is left and right.

The self-inductance potential of the direction supplies power to the load. When the feedback voltage of the U17(2) pin is lower than 5V, the internal switch is turned on and the regulated voltage is 5V.

Note: U17(1)EN pin control voltage 3.75V, (3) external compensation component, establish voltage control error amplification circuit through external RC component output, realize OSC oscillation frequency control, oscillation frequency 340KHz, output current 3A.

VBY1 power supply part

In the circuit, Q15 is the control, U16 the electronic switch. When the power is turned on, the main chip U8 (N5) pin outputs PANEL_ON high level voltage to make Q15.

Saturated on, 12V voltage is divided by R209, R204, U16 turns on 12V voltage through U16 source and drain, and is sent to the screen via VBY1 socket

The control panel acts as the operating voltage for the control board.

Control section

On/standby control circuit

When the TV is in the standby state, the PWR_ON/OFF control voltage output from the U8 (N6) pin is high, and the control power board 12V is not lost.

When the TV is normally turned on, the PWR_ON/OFF control voltage output from the U8 (N6) pin is low, and the 5V standby voltage is controlled by R19.

The source board 12V has an output.

Backlight start control

When turned on, the U8 (R6) pin BL_EN outputs a low level to turn off the Q13 transistor, and the 5V_USB voltage is sent through the R18, R56 3.3V voltage.

The backlight driving circuit starts the backlight driving circuit and turns on the backlight. If the voltage is zero, it indicates that the backlight cannot be lit. The reason should be in the movement.

Backlight brightness control

When turned on, U8 (R5) pin BL_ADJ output PWM is amplified by Q10 transistor, D5V voltage is sent through R111, R113 3.3V voltage

The backlight driving circuit starts the backlight driving circuit to provide a driving pulse signal for the backlight, so that the Q10 and related circuits are faulty the backlight driving circuit stops working, and there is no grating, no image, and there is a sound fault. (NC means there is no such component).

Remote control circuit

When the remote control receiver output control signal is sent to U8 RTD2995D (T5) pin, the CPU receives the command signal and starts to work. U8 output is high.

The low level causes the indicator to flash, and the red indicator on the remote control head should be constantly lit when the TV is in standby.

The infrared receiving head may also be damaged. Use the oscilloscope to detect at R28 and press the remote control. If there is a waveform display, the remote receiving head is normal.

The waveform indicates that the remote control receiving head is damaged, and the normal remote receiving head is replaced for reconfirmation.

 DDR circuit

DDR is a frequently problematic component. For DDR, when the program is running, “BIST” will appear. “BIST” is the meaning of Build In SelfTest. Thinking is the automatic detection of the DDR module by the chip power-on. The BIST is completed and will automatically find the best phase value.

BIST: OK - indicates that the primary test passed.

BIST: Fail - indicates that the primary test failed. There is a problem, most of the power supply's 12V power-on time is relatively long, resulting in the DDR part during initialization.

It has not been started yet. It is a hardware problem with abnormal VCC power supply. Performance is not booting.

Maintenance Tip: Regarding the failure of the amplifier, it shows that there is no sound from the speaker. First of all, make sure that the amplifier itself has no bad solder joints and have continuous soldering. Secondly Analyze whether it is other hardware reasons, including the 12V power supply of the power amplifier, whether there is output on the left and right, and finally see if MCLK, SCLK, etc. are positive.

Common fault repair and maintenance method.

For the movement board, first of all, visually check whether the material is inserted correctly, whether there is a bad solder joint or a joint weld. After eliminating these human factors, then Confirm the board hardware or software issues. For hardware, first the power supply should work properly. 5V Normal and 5VStb ripple are less than 100mV,

The VDDC, 1.5V, 3.3V, 2.5V ripple is less than 50mV.

No power failure troubleshooting ideas

1, first determine whether the fault is on the motherboard or on the power board

The 5V-STB output from the (7) pin of the movement board CN8 is the standby voltage. If there is no voltage on this pin, the fault is on the power board. (10) The foot is the movement

The board is sent to the power supply's open standby voltage. If it is turned on twice, the measured (10) pin voltage can be changed from low level to high level. If CN8 (7) pin is lost, the 5V-STB is the standby voltage. It should be determined that the power-on fault is not on the components on the power board. If the measured (10) pin voltage cannot be changed from low level to high level.

If the level is above 2.5V, the fault will not be turned on the movement board.

2. Check the devices on the motherboard

First, check whether the appearance color of the IC on the motherboard is abnormal, whether there is crack on the surface, and secondly, check whether the magnetic capacitor and the electrolytic capacitor foot are off, and the surface.

Whether it is bulging or cracking. The third is to check the AV; HDMI; VGA and other port anti-static components are not cracked, etc., the fourth is to measure the main chip pin-to-ground resistance, in order to judge whether the TC is broken down,

3. Force the power board assembly to check the power supply.

In order to confirm the fault location, the power module can be forced to open, the RTD2995D movement board is characterized by the movement component control unit assembly output only 12V

The output voltage is sent to each DC/DC block on the main board and the three-terminal voltage regulator. When working, the VDDC of the core board, NOYMAI voltage and FLASH, DDR are measured.

4. Check the clock oscillation circuit and reset circuit of the main chip. The reset circuit is a necessary condition for ensuring the normal operation of the main chip. When checking the reset circuit,  measure the reset pin voltage at the instant of power-on, can from the high level to the low level, when checking the clock oscillation circuit, it is mainly to measure the voltage or waveform at both ends of the crystal oscillator, or to replace the crystal.

5 C heck whether the transmission channel is smooth between different integrated blocks

The transmission channel between the integrated blocks of the LCD TV must be unblocked, especially the information transmission channel between the FLASH block and the user memory.

FLASH block, 5 SPT digital signal waveforms or voltages are hopping to confirm whether the control system operating conditions are true, and the total tuning is turned off.

The line is connected across the resistor to verify that the load on the I2C bus is faulty. The bus voltage is usually around 3.3V.

6 Refresh the FLASH block program

Program changes in the FLASH block will also cause no power-on failure. For the FLASH block program, the near-line refresh can eliminate the data change.

Most of the flat-panel TVs have USB ports, are basically open, and use USB ports for software upgrades. Of course, a TV that have not a normal standby process cannot be software refreshed through the USB port. It can only use the programmer to write programs to the FLASH block.

7 Replace the chip or motherboard

If the fault cannot be eliminated by the above method, the fault can only be corrected by changing the main chip FLASH memory and the user memory or the main core board.

Maintenance case

1) fault: no boot, the indicator light is on.

Analysis and maintenance: The test start-up voltage is 4.5V, but the screen power supply 12V voltage is 0. Firstly, the voltage of each part of the core board is measured, and the bus voltage is normal.

In the principle of soft first and then hard, software upgrade or FLASH memory block, after the fault is finally replaced, the TV works normally.

2) fault: automatic shutdown, crash, standby does not boot.

Analysis and overhaul: 12V, 5V, 3.3V, normal power supply, main chip U9, U205, U2 power supply normal measurement U103 (1) foot voltage 3.3V, positive often 1.5-2.5 jitter, may be the flash chip write protection state, replace the FLASH memory block (note, replace the core that must carry data Tablet) After the replacement, there is an image, screen, which needs to be upgraded.

3) fault: the screen is reddish when connecting VGA.

Analysis and repair: When the VGA appears, the picture is reddish. Go to the website to download the software upgrade.

Power primary

5VSB, 12V rectified output, feedback sampling circuit, voltage regulator circuit, power supply ON/OFF circuit, LED driver circuit, LED chip power supply, LED overvoltage protection circuit

Power board maintenance method and maintenance flow chart

Protection function introduction (OVP overvoltage protection, OCP overcurrent protection, OPP overpower protection, LUVP undervoltage protection)

AC input overvoltage protection OVP

The varistor VR1 in this protection circuit, when the input voltage is higher than its specification voltage value

When VR1 is short-circuited, the current between LN increases rapidly, causing F1 to open.

AC input under voltage protection LUVP

AC power failure detection consisting of R128, R129, R130, C101, R124, U100 and Overvoltage monitoring circuit, When the PIN 3 voltage of the U100 reaches 1.05V, the PIN3 protection function is turned on. When the PIN3 voltage is lower than 0.8V and higher than 6.0V, the LD7537 chip Turn off the PWM output so that 5VSB and VCC have no output for protection purposes.

OCP&OPP

12V/5Vsb OCP (over current protection) Pin by sampling resistor R115 and R120, C102 and U100 4 constitutes an output overcurrent protection circuit. When the output current is too large, causing The current flowing through R115 is large, causing a large voltage difference of R115, and the PIN4 voltage of U100 ≥0.85V, U100 Off, thus achieving protection purposes.

5Vsb, 12V OVP

The feedback sampling circuit and the U100 VCC power supply circuit form a 5Vsb, 12V output overvoltage protection circuit. When the 5Vsb output reaches 7V or higher, or

When the 12V output reaches 14.5V or higher, the output voltage is fed back to U100 through the feedback sampling circuit, and the VCC power supply circuit supplies U100 PIN5 voltage to increase.

When U100 PIN5 voltage is higher than 26V, U100 off, so that 5Vsb, 12V no output, for protection purposes.

VLED OVP

Composition of Q6F, R31F, R32F, R30F, R29F, R28F, R53F, R26F, R25F, R52F, R33F, R34F, C14F, R36F, U2F, R35F, C6F 12V, 5Vsb output overvoltage protection circuit. When the VLED output reaches 200V or above, the Q6F base voltage is raised. When the Q6F base current is reached, the voltage is reached.

When the value is constant, the Q6F is turned on, the voltage difference of R31F is increased, the voltage of PIN7 VS pin of U1F is increased, and when the voltage of PIN7 is greater than 1.25V, the protection is performed.

The road starts to move, U1F OFF, so U1F does not work, VLED has no output, and achieves the purpose of protection.

Software upgrade method (provided by model manager)

Normal upgrade method

1. Copy the software to the root directory of the U disk and change the file name to: install.img

2. Insert the USB flash drive into the TV USB port, press the menu button on the remote control, and then press 8893 to enter the Haier factory menu home page, move the cursor Go to the Rtd2995 upgrade and press the OK button.

After pressing the OK button, there will be a prompt, select the confirmation button, the software will be automatically upgraded, and the machine will start automatically after the upgrade is completed.

Abnormal upgrade method

1. Copy the software to the root directory of the U disk, change the file name to: install.img, and insert the USB disk into the TV USB interface.

2. Press and hold the menu button on the control panel, then press the TV's AC switch to set the TV to off, and then enter the upgrade interface after the TV enters the upgrade interface.

The menu button on the board is released.