Lcd / Led technology will be more difficult for beginners, because everyday they will be dealing with various brands and models. From the old school to the last product. From simple economical products, to sophisticated and intricate.
Some use single Psu, and some use Dual Psu
Some use a separate Psu-Inverter-Motherboard board, and some use only one board.
There are Microprocessors that are separate from the Video Processor, and some have been combined into a single chip.
The use of IC Nand Flash and Emmc memory on the new models, while the old models still rely on IC Flash memory.
The use of external RAM ic and some use internal RAM so the unity in the ic chip.
KINDS OF VOLTAGE REDUCING REGULATORS IN THE MOTHERBOARD
We start to understand the types of powersuply regulator ic found on the motherboard. The motherboard circuit requires a variety of voltages. For this purpose, the input voltage supply to the motherboard must be converted / converted to various voltages whose values can be different, for example 5v, 3.3v, 2.5v, 1.8v and 1.2v.
Lowering regulators used in motherboards can be categorized into two types, namely:
LDO
Dc-Dc
LDO (Low Drops Out Regulator).
It is a regulator whose work is almost similar to the 7805, 7812 which we have often encountered on CRT TVs. There are various forms, some are similar to a 3 leg transistor, some are shaped like an 8 foot memory ic, and some are in the form of a small 5 foot ic.
LDOs generate less heat than regulators such as the 7805.
Generally, the maximum is only capable of providing a current of less than 1A.
In the use of "Input and Output voltage difference" LDO should not be too large. For example, it should not be used to reduce the voltage from 12v to 3.3v. It should only be used from 5v to 3.3v for example. Because the greater the difference between the input-output voltages, the hotter the regulator. LDO circuits are quite simple because they do not require many external components.
There are 2 types of LDO output:
FIXED or fixed output voltage. For example voltage2: 5v, 3.3v, 2.5v. 1.8v
The output voltage can be verified by changing the value of the external resistor component.
LDO with on-off control
There are LDOs that are not controlled on-off, for example, such as 7805, 78012
There are also types of LDOs that have an on-off control pin, for example, the 78R05, 78R12.
It is a regulator that works similar to how a switching regulator works.
The shape is similar to an 8-foot memory ic, some are smaller and have 6 feet.
The characteristics of dc-dc ic is the presence of an inductor (coil) that is nearby.
DC-dc generates very little or no heat, so it doesn't require cooling. The maximum current is generally capable of up to 3A.
The large difference between the Input and Output voltages does not cause problems (no heat), for example from 19v to 1.2v. Of course, things like this cannot be done using LDOs.
Compared to LDO, dc-dc has a slightly more complex circuit, requiring more external components.
MOTHERBOARD IS OFF TOTAL or DOES NOT WANT TO STBY
What to do if you find a completely dead motherboard.
Here we only limit discussing what needs to be checked so that the Microcontroller is ready for Power-on.
Important points that must be examined in full is to understand the order of work of the Microprocessor from the time it is plugged in until it is ready to turn on:
The Microprocessor receives a Stby 3.3v and 1.2v Vcore supply voltage
The Microprocessor receives the HW RESET voltage (Hard Ware reset)
The Microprocessor generates system clock pulses with the help of X.tal oscillator.
The Microprocessor communicates with the SPI Flash memory via the sda / scl line.
The Microprocessor is ready to get commands from the control input system.
* There is one more thing to remember, because this one does not use all motherboards, namely the Microcomputer needs to get AC_det voltage input.
UNSWITCHED and SWITCHED REGULATORS
Many beginners make mistakes in doing analysis ………
Found one or more of the voltage regulators on the motherboard that hasn't appeared yet ………
Then focus the tinkering on that part …… .. In actual fact that part doesn't matter …….
How could this happen ???
LDO and Dc-dc regulators can be divided into two, namely:
UNSWITCH (not switched), which is the Stby voltage which is always there when the power plug is installed during standby or on. This is the voltage required for the microcon section to work. The voltage for standby generally requires 2 types, namely 3.3v and 1.2v
SWITCHED (can be switched), the output voltage can be switched "on-off". This voltage only appears when the aircraft is power-on. Here the microcontroller will issue a voltage command "POWER_ON" so that the regulator will issue an output voltage.
Finding the total dead problem, then you must first focus on the UNSWITCH voltages.
TRACKING STBY VOLTAGE
Generally, 2 kinds of unswitched voltages are needed for standby, namely 3.3v and Vcore 1.2v
3.3v unswitched to supply IC Chips / Microcons, Memory, remote sensors. Can use the LDO or Dc-dc types. Its presence is easiest to check on the Vcc-ic Flash memory pin or on the Vcc remote sensor leg
Vcore 1.2v always uses dc-dc. Because here it takes a large current up to 3A. Without the schematic it is difficult to determine which Dc-dc is for V.core. But you can try to find it by trying to measure all the Dc-dc that is on standby. If you find 1.2v, that's the V.core scene. If you still don't find the possibility of a short Dc-dc output, just try to measure all the existing dc-dc outputs with an ohm meter, and you'll find a short one. It could be caused by a short filter output capacitor, short ic chip, or damaged dc-dc
STBY VOLTAGE
Generally, the Microprocessor gets 2 kinds of supply voltage UN-SWITCH 3.3v and Vcore 1.2v
3.3v - Sometimes you get it directly from Psu, some use Dc-dc stepdown, some use LDO. The voltage can be checked on the Vcc ic Flash pin-8 or at the Vcc Remote sensor.
1.2v - Vcore is obtained always using Dc-dc stepdown. Because here a large amperage (3A) is needed.
Without a schematic it is difficult to determine which Dc-dc for V.core.
But you can try to find it by trying to measure all the Dc-dc that is on standby.
If you find 1.2v, that's the V. core voltage
If you still can't find it, chances are Dc-dc is short. Just check all available Dc-dc outputs with an ohm meter. If you find someone who is short, that's most likely Dc-dc V.core. It could be because the components in the Dc-dc output line are short, such as the filter output capacitor, ic chip, or the Dc-dc ic itself is damaged.
Vcore drops are sometimes caused by a damaged ic chip.
HW RESET.
A computer hardware reset or hard reset is a hardware operation that re-initializes the core hardware components of the system, thus ending all current software operations in the system. This is usually, but not always, followed by booting the system into firmware which re-initializes the rest of the system, and restarts the operating system. A hardware reset is an important part of the startup process for the microcon to be ready for "power-on"
Reset can also be triggered by direct intervention via the "reset button" located on the motherboard
Unlike CRT TVs, Lcd / Led generally get an active reset voltage "High". This means that as soon as the power plug is installed the Reset pin will get a "high" voltage for a moment it continues to disappear.
Reset Voltage can be checked in the following manner:
Pin-Reset can be found through the ic chip datasheet used.
Install the avo first, to measure the pin-reset voltage.
Recently the power plug was installed.
Normal voltage will appear for a moment. It can be seen with the avo needle slightly wobbling. Henceforth after the TV is on, the normal pin-reset voltage is zero.
Reset circuit can only be known by looking at the schematic of the model concerned. Some use ic and some use transitor only.
.
X.TAL OSCILLATOR
Oscillating action provides the system clock pulses.
The most accurate way to check the presence of clock pulses is with the help of an oscilloscope. But if there is no oscilloscope, it can also, even though it is not 100% correct, check for the presence of voltages on the Xtal leg. Generally around 1.25 - 1.75v
DATA COMMUNICATION WITH SPI FLASH
Data communication microcons with IC SPI Flash through the SDA / SCL line to be able to Read & Write data. These two lines usually have a voltage of around 3v and must be the same.
Every time after the power plug is installed, the Microprocessor will read the SPI Flash memory data and upload the data into the RAM memory system which is internally inside the Microprocessor itself. If the Microprocessor fails to communicate with IC SPI Flash or FW data ic Flash error, then the Microprocessor will fail Stby.
Conversely, when the TV is turned off, the Microprocessor will write back data into the SPI Flash ic. Where here the data may have been changed, for example image mode data, voice mode data, or maybe sermod data etc.
Sometimes the communication system from Microprocessor to is SPI Flash can also be disrupted due to poor connection. Or sometimes if you use something like R the jumper is delayed.
Data error problems are most often found on LCD / Led compared to CRT TV, which causes the Microprocessor to fail. Maybe this is because the FW data is very large compared to CRT TV data. So that there is a greater possibility of errors when Read or Re-write.
INPUT SYSTEM
Although it rarely happens, it is possible that the Mikrokon will not function only because the command from the INPUT system is problematic. There are 2 sources of input command, namely
IR sensor.
Key-in.
The most frequently found damage in this section is the presence of a leaky or short C smd. Sometimes we also find dirty pcb problems on the lines between the pcb control and the ic chip.
AC_DET
Not all models are equipped with an AC-det circuit. The AC_det circuit is in the primary Psu section, monitoring the AC voltage input voltage is healthy or not. The AC_det voltage is inputted from the primary Psu via the Photocoupler to the secondary Psu, …… .. and then to the Mikrokon. Normal if AC-det is healthy there is a voltage of about 3-4v to the Mikrokon.
If the Microprocessor has no AC-det, the Microprocessor will fail to standby.
You could say AC_det is similar to an AC-input voltage protective circuit. If the AC-input voltage drops below a certain level, the Microprocessor will shut off.
Sometimes the technician, if he is bothered to track down looking for damage to this section ... ... just keep looking for an easy way .... that is to provide a fixed voltage on pin-AC_det.
Microprocessor failure can also be due to damage to the IC chip or problems with the soldering of the chip feet that have lost contact.
Chips with signs when touched is hot. Means it can't be helped unless you have to replace the chip.
we examined how the steps of the Microprocessor section work so that they are ready to be "Power on-off control". These are only a fraction of the motherboard functions, so we have a lot to cover.
What are the next stages to understand & learn.
So we invite again to understand the stages on CRT television, which are roughly as follows:
The Microprocessor issues a "power-on" command to the circuit switch on or regulator 8v and 5v.
8v and 5v voltages are present.
8v to supply voltage Horizontal start.
And 5v for audio / video circuits for chroma ic processors, tuners etc.
Got "8v" the Horizontal section will start working, continue until the Flyback gushes.
The vertical part of the flyback will get Vcc supply, and the CRT will get a Heater, Screen, Focus, 180v supply voltage.
The vertical part begins to work….
And the CRT screen is ready to turn on, but while still on MUTE.
Then Chroma outputs an RGB image signal ... ... and the screen appears.
Likewise on Lcd / Led.
Microprocessor stages have been passed and ready for Stby.
After pressing the power button,
Then the Microprocessor will output the "power-on" control which will function to turn on several regulators that are SWITCHED to provide various voltage supplies in parts, such as SCALLER (Video processor), Tuner, ic RAM (DDR2), ic Eeprom etc.
.
The red line is the UN-Switch 3.3v and 1.2v voltages for the Microprocessor section.
Lcd.Led remote sensors made in China generally get 5v voltage. Meanwhile, those made in Korea and Japan generally get 3.3v.
The blue line is the supply which is switched on-off. Output voltage 3.3v for Audi / Video processor, Eeprom memory, Tuner and 1.8v voltage for RAM memory (internal).
Audio ICs can generally be Vcc 12v directly UN-Switch, but for 3.3v supplied from a controlled on-off.
On old LCD / LEDs or large screen TVs which still use a separate Psu module from the motherboard, generally they still use 2 kinds of powersuply circuits.
Small powersuply to provide motherboard Stby voltage
Main Power Supply (large) to supply voltages to other motherboards.
Here the "power-on" command from the motherboard is required to turn on:
Main power supply.
PFC circuit.
Many beginners don't understand.
Check the main powersuply has not issued a voltage. Continue to search for the cause.
In fact, Powersupky has no problem. The motherboard is the problem, because it hasn't issued a power-on command to Powersuply Main or it's still Stby.
DAMAGE TO SWITCH ON-OFF VOLTAGE REGULATOR.
If any of the voltages does not come out or drops, it can cause various symptoms of damage such as:
The indicator is green, but the picture and sound are not there
Restart repeatedly.
Just jammed up the logo.
Live or die alone.
Or maybe dead stby protection
Symptoms like this can all vary in different modes. depending on the design of each manufacturer / brand.
- The Stby light can go out or turn green when it is turned on.
All motherboard voltages that are switched on-off are present.
Then the next process, the Microprocessor will output the controls as follows:
Inverter_on which will turn on the BL (backlight) lamp
Panel_on which will control the "Vcc Tcon Switch panel" to output a voltage of Vcc 5v (if the panel is small) or 12v (if the panel is large).
PWM_dim which will control the brightness of the BL lamp.
Simultaneously with the active PWM_dim, the LVDS image data starts to actively output the image signal to Tcon ..
Some models will immediately appear images. But there are also those that will display the LOGO first, then a few seconds later the image appears.
All settings for the working sequence of the Microprocessor as described from , until the logo and TV images come out are all arranged using FIRMWARE embedded in flash memory ic. Therefore, if a problem occurs in the working order or gets stuck in the middle of the road, it could be due to damage to DATA FIRMWARE or due to damage to the Flash memory ic.
Process like the above is a standard process.
In certain models there may be additions or differences, for example
SONY
If the LVDS to Tcon cable is not installed or the panel installed is not Sony originals. So after Panel_on, the process will stop. And the plane is dead in protection with a blinking code,
CAN BE SEEN ON SHARP, TOSHIBA, PANASONIC Japan models
After Inverter_on, if it turns out BL doesn't turn on..........
--------------------------------------------------------------------------------------------------------------------------------------
How the microcontroller work process starting from the moment the electricity is plugged in so that the screen can turn on to output an image.
In the CRT TV technique as example , this is the same as the work process, starting from the electricity being plugged in until the Flyback bursts and the CRT screen turns on.
This time we will discuss the problem of processing the VIDEO image signal so that the motherboard can output the LVDS image signal to be fed to the Tcon input. To make it easier to understand, we made a simple Main Block Diagram on the VIDEO image signal process on the Motheboard.
No.1 ANALOG Input.
Analog input can be various, each model can be different.
Input signals from the RF antenna, Video Composite (Y, Cr, Cb) or Video-in are processed first by the VIDEO DECODER section to obtain an RGB signal.
No.2 PC (RGB) Input
Tube television hardly recognizes this type of input, namely analog RGB input. Through this input TV LCD / LED can be used as a PC computer monitor
No.3 A / D Converter.
Here the Analog RGB signal needs to be converted into a Digital RGB signal before entering the next process.
No.4 HDMI
HDMI is a digital data interface communication standard for Digital Audio / Video equipment. Other equipment which has an HDMI output can be connected directly without going through the Converter A / D circuit.
No.5 SCALER
This is a vital part of the motherboard's digital image signal processing before it is fed to the LCD panel.
In the Crt TV technique, RGB signals can be connected directly to all types of Crt. Want big or small crt. Want low resolution or high resolution CRT, everything can be done without the need for changes (converted)
In different LCD techniques.
There are various kinds of video input FORMAT with different image resolutions. Suppose there is a PAL video signal. NTSC, SECAM, MP4, GAME etc.
While the Lcd panels are made with different resolutions, such as HD, FHD, K4
The input RGB digital video signal cannot be fed directly to the panel. Each format must be changed (converted) first to match the panel resolution used. That's what SCALER is for.
Input resolution is generally lower than panel resolution. Because of that Scaller is sometimes also called UpScaler Conversion.
In this section also the ASPECT RATIO video image signal can be changed in appearance size, for example a 4: 3 size TV image is changed to a wide 16: 9 size etc.
No.6 RAM
In the process of working, Scaler requires the help of high capacity RAM memory ic, which is sometimes called DDR RAM or SDRAM. Input digital data cannot be directly displayed to the output section. The input data is written first to IC RAM during the process, then after it is perfect, it is read to be outputted.
The higher the image resolution, the greater the capacity of the IC RAM that is bleached. RAM is integrated internally with the ic chip. While external RAM, sometimes there are motherboards that use only one piece, and sometimes there are those that use two.
IC Chip with external RAM communication with each other using several lines. Sometimes it is found that one of the paths has a problem, such as the R value is delayed, resulting in a defective image / osd.
No.7 LVDS.
Moving image data is a data transfer that requires very high speeds. The higher the image resolution, the higher the data transfer speed required. This causes various kinds of problems, such as (a) the need for more band-width, (b) the use of more electrical power, (c) causing high frequency noise interference.
LVDS or Low Voltage Differential Signaling is a data-transfering system technology that is able to answer the problems mentioned above.
LVDS characteristics are:
Data-transfer at high speed
The amplitude of the data signal is small, about 200 to 300 millivolts
Low power requirements
Little noise
Works at very low low voltage
Uses a pair of twisted wires and does not use ground as the reference signal
The data sent is serial-data, so it can reduce the number of connector cables
Here RGB digital data is converted (encoded) by the LVDS Transmitter to become an LVDS data signal. The LVDS data is an analog signal, so a low frequency oscilloscope can track its presence.
Therefore, the LVDS data will be received by the LVDS Receiver and converted back (decoded) into a digital RGB signal.
SOME EXAMPLES OF DAMAGE TO PICTURE SIGNAL LINE.
IC Chip with external RAM communication with each other using several lines. Sometimes it is found that one of the paths has a problem, such as there is an R value being delayed, resulting in a defective image / osd.
Image / OSD defects can sometimes also be caused by Vcc ic RAM drops.
The LVDS data path is damaged or cut sideways, causing the image to color way, depending on which path is broken.
Damage to the LVDS line can also cause the image to become out of sync (collapsing), because there is also a vertical / horizontal synchronization path. Seing found at old SONY.
Understand the example of a motherboard block. Then we will know which part we think is problematic. For example the HDMI input is OK no problem. While the other Input2 has a problem. So it is clear here that the damage is in the DECODER section.
Flash memory ic data also plays a role in determining the working system of the Scaler. Therefore, FW data errors can cause defective images.