Technical description and composition of the HARPER 28R575T TV, panel type and modules used. The composition of the modules.HARPER LED
Model: 28R575T
Chassis / Version: HK.T.RT2957P68
Panel: KM0275LDHH00004
LED backlight: JL.D27551235-269AS-M
LED driver (backlight): integrated into MainBoard
PWM LED driver: 8 pin
MOSFET LED driver: TO-252
Power Supply (PSU): integrated into MainBoard
PWM Power: PWM SOT23-6
MOSFET Power: TO-252
MainBoard: HK.T.RT2957P68
IC MainBoard: SPI Flash: 25q32; SOUND: TPA3110LD2
Tuner: NoName
Specifications 28R575T
HARPER 28R575T
General recommendations for TV LCD LED repair
Possible manifestations of defects
- HARPER 28R575T does not turn on and does not show any signs of operability at all. Does not blink indicators and does not respond to control buttons.
In this case, first of all, you should check the operability of the main power source - AC / DC voltage converter, all elements of which are located on the MainBoard HK.T.RT2957P68. Then we recommend measuring its output voltages and, if they are absent, check the serviceability of the power switches (TO-252) and rectifier diodes of the converters for a possible short circuit.
In the event of diode breakdowns in the secondary circuits, the converter can operate in an emergency mode of short circuit without output voltages, and with a short circuit in the power elements of the primary circuit, the mains fuse and / or current sensor in the source of the key usually breaks off.
Mos-Fet power switches used in switching power supplies sometimes fail due to a malfunction of any other elements that can disable it in the key mode, or create an excess of the maximum permissible key parameters. These can be elements supplying a PWM regulator, frequency setting or damper circuits, or elements of negative feedback in the stabilization circuit. PWM controllers PWM SOT23-6, in the absence of visible damage or outright short circuits between the terminals, are checked by replacing them with new ones, or knowingly working properly.
- There is no picture, but there is sound and all other functions work. Sometimes, when turned on, the image appears and disappears for a second.
The backlight of the matrix (LED-panel) is usually faulty in these cases. The reason for this may be an open circuit in the LED circuit, or a problem in stabilizing their power supply.
It is impossible to check the LED bars for a break without disassembling the panel with a multimeter or tester. For these purposes, it is necessary to open all series-connected PN junctions and a voltage of the order of tens of volts will be required, and ideally a current source. Having disassembled the panel, it is necessary to check each LED separately. Chinese multimeters tend to light a single 3V LED in the forward direction. In the case of using dual 6-volt LEDs, the PN junction of its protective zener diode can serve as an indicator of serviceability. In faulty LEDs, the zener diode will either be cut off, or pierced in the K / Z.
- The indicator blinks or is on constantly, the TV does not turn on, does not respond to the remote control.
Repair or diagnostics of the HK.T.RT2957P68 motherboard should begin with checking the stabilizers and power converters necessary to power the microcircuits and matrix. If necessary, you should update or replace the software (software). Complex repair of MB (SSB) board is in some cases possible and practiced by repairmen. To do this, check and, if necessary, replace the SPI Flash elements: 25q32; SOUND: TPA3110LD2. Malfunctions in BGA chips are usually easy to detect by warm-up.
Before changing the tuner NoName, if it is not possible to tune to television channels, you should make sure that there are supply voltages, which must be measured at the corresponding terminals of the tuner and check the software for correctness. The pulses of the data exchange of the tuner with the processor can be monitored with an oscilloscope
Once again, we remind TV users: do not attempt to repair yourself without the appropriate knowledge, experience and the necessary qualifications! Trust the repair to professionals with sufficient experience in the field of electronic repair.
DOWNLOAD FIRMWARE FOR SPI FLASH -----------> HARPER 28R575T, Main: HK.T.RT2957P68, Panel: KM0275LDHH00004
The appearance of the MainBoard HK.T.RT2957P68 is shown in the figure below:HK.T.RT2957P68
The main features of the HARPER 28R575T device:
Installed matrix (LED panel) KM0275LDHH00004.
To power the backlight LEDs, a converter combined with the main board HK.T.RT2957P68 is used, controlled by an 8 pin PWM controller. TO-252 switches are used as power elements of the LED driver.
The power module is combined with the MainBoard and is made according to the AC / DC flyback voltage converter using SOT23-6 PWM microcircuits and TO-252 power switches.
MainBoard - the main board (motherboard) is a HK.T.RT2957P68 module, using SPI Flash chips: 25q32; SOUND: TPA3110LD2 and others.
Tuner NoName provides reception of television programs and tuning to channels.
TV HARPER 28R575T with LCD display KMO275LDHH00004, diagonal size 27.5 "(70 cm) 16: 9 format. The required screen brightness of 200 cd / m² is provided by LED backlighting. Dynamic contrast ratio of 60,000: 1 is achieved by special control of LED operation. The screen of this TV model is realized with LED backlighting.It is possible to view images in high quality HD at a resolution of 1366x768 pixels in the standard graphic decomposition of 720p (HD Ready) .Supported multimedia file formats: MP3, MPEG4, JPEG.
Speaker power 14 W (2x7 W) is provided by two speakers. The NICAM STEREO audio processing system is used.
External interface (communication with other devices) is supported by standard input and output connectors: antenna input (RF), AV, audio x2, component, VGA, HDMI x2, USB. A headphone output is provided.
The digital tuner is capable of receiving television channels in the DVB-T MPEG4, DVB-C, DVB-T2 standards.
The power consumed by the TV operating in mains mode is 55 W.
Dimensions: with stand 643x432x186 mm, without stand 643x390x76 mm.
TV weight: 4.2 kg.
Attention! Panel KMO275LDHH00004 LED-TV HARPER 28R575T is an expensive and unreliable element.
Do not allow any impacts on the glass and pressure on the screen surface to avoid damage to the LED panel!
It is also unsafe for liquid to spill onto the screen. Sometimes one drop is enough if it drips down the glass onto the cables to make the TV non-repairable.
