Technical description and composition of the BBK 28LEM-1044 TV, panel type and modules used. The composition of the modules.BBK LED
Model: 28LEM-1044
Chassis / Version: CV512H-U42
Panel: ST2751A01-8
LED backlight: JS-D-JP2820-051EC (71220)
T-CON: ST3151A05-8
LED driver (backlight): integrated into MainBoard
PWM LED driver: BIT3267
MOSFET LED driver: ME15N10-G
Power Supply (PSU): integrated into MainBoard
PWM Power: PWM SOT23-6 AP3125
MOSFET Power: 7N60 TO-220F
MainBoard: CV512H-U42
IC MainBoard: SPI Flash: W25Q64, Audio: RDA3118E28 (TPA3110D)
Tuner: CDT-9NT372-RD60
Specifications 28LEM-1044 / T2C
BBK 28LEM-1044
General recommendations for TV LCD LED repair
Possible manifestations of defects
- BBK 28LEM-1044 does not turn on, indicators on the front panel do not light or flash. The TV does not respond to the control buttons and the remote control.
First of all, in such cases, you should make sure that the common switching power supply (SMPS) - the AC / DC voltage converter of the mains voltage - is working. All source elements in this TV model are located on the MainBoard CV512H-U42. Its output voltages should be measured and, in their absence, the power switches (7N60 TO-220F) and rectifier diodes should be checked for the probability of a short circuit in the converters.
In case of breakdowns of semiconductors in the secondary circuits, the converter can usually work in an emergency in the short-circuit mode, and with a short circuit in the power elements of the primary circuit, the mains fuse often breaks.
Mos-Fet keys used in switching power supplies usually fail due to a malfunction of other elements that can disable it in key mode, or provoke an excess of the maximum current or voltage values. These can be circuits supplying a PWM controller, damper or frequency setting circuits, or OOS (negative feedback) elements in the stabilization circuit. PWM controllers (PWM) PWM SOT23-6 AP3125, in the absence of external damage and short circuit between the terminals, are checked by replacing them with a known good one.
- There is no picture, but there is sound, it reacts to the remote control. Or the image appears when turned on and immediately disappears
A malfunction is usually in these cases most likely in the backlight units of the display matrix. Often the cause of a malfunction is the lack of current in the LED circuit, for example, their open or short circuit, or a violation of the contact connections of the connectors.
It is impossible to check the line of series-connected LEDs without a special current source, and it is unsafe for them to use any voltage sources above 12V for this purpose. Then all that remains is to open the panel and check each LED separately. Typically, Chinese multimeters with a 9V power supply lightly light up one 3-volt LED if you connect the probes to it in the forward direction, the red probe to the anode, and the black one to the cathode. For dual 6-volt LEDs, the PN junction of its emergency zener diode can serve as an indicator of LED health. In the event of a malfunction of the LED, its zener diode will either be cut off, or broken through in the SC.
- The indicator on the front panel blinks, the TV does not turn on in operating mode, does not respond to the remote control.
Repair or diagnostics of the CV512H-U42 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). If it is not possible to replace the MB (SSB) board, you need to check the serviceability of its elements - SPI Flash: W25Q64, Audio: RDA3118E28 (TPA3110D). Defective components must be replaced.
If there is no reception of television channels, but the TV is working properly from external devices, first of all, you need to check the supply voltage of the CDT-9NT372-RD60 tuner and update the software. I2C communication pulses must be monitored with an oscilloscope.
If the BBK 28LEM-1044 / T2C has no image, but there is sound, the backlight of the ST2751A01-8 display often simply does not work. Moreover, in LED TVs, the LEDs inside the panel usually fail, less often the LED driver.
In such cases, you can see a barely noticeable image with a successful hit of external light on the screen.
Replacing the LEDs requires disassembling the ST2751A01-8 LCD panel - a process that requires experience and qualifications from the master. We do not recommend doing such work on your own to the owners of TVs and craftsmen who do not have experience in repairing LCD panels
If there is no image, and the backlight is on, the screen becomes slightly lighter when turned on, and in an open TV you can see light through the holes in the panel case.
In this case, the panel may also be faulty - damage to strips, loops, for example, as a result of moisture ingress after unsuccessful washing of the screen, the T-CON (Timing Controller) board may be faulty. But the main board MainBoard CV512H-U42 often turns out to be faulty, a software failure is also possible.
Then, first of all, you need to check the panel supply voltage, the fuses on the T-CON board, as well as the supply and reference voltages of the column and line drivers - VGH, VGL, Vcom.
If these measurements are within normal limits, it is necessary to trace the passage of LVDS signals from the MainBoard CV512H-U42 with an oscilloscope, as well as synchronizing signals to the loops with drivers.
Flooded or unsuccessfully washed screens of LED TVs can be restored, in about half of the cases, usually if significant damage has not formed in the loops and panel strips.
Additional MainBoard RepairAttention to users! Self-repair of the BBK 28LEM-1044 TV without the appropriate qualifications and the necessary experience can lead to its complete non-repairability!
The appearance of the MainBoard CV512H-U42 is shown in the figure below:
CV512H-U42
CV512H-U42 can be used in TVs:
DEXP H39D7000Q (Panel LC390TA2A), SUPRA STV-LC32LT0010W (Panel KM0320LDRH0037).
The main features of the BBK 28LEM-1044 device:
Installed matrix (LED-panel) ST2751A01-8.
Matrix control uses the ST3151A05-8 Timing Controller (T-CON).
To power the backlight LEDs, a converter combined with the CV512H-U42 main board is used, controlled by the BIT3267 PWM controller. The keys of the ME15N10-G type 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 PWM SOT23-6 AP3125 chips and 7N60 TO-220F power switches.
MainBoard - the main board (motherboard) is a CV512H-U42 module, using SPI Flash chips: W25Q64, Audio: RDA3118E28 (TPA3110D) and others.
Tuner CDT-9NT372-RD60 provides reception of television programs and tuning to channels.
Additional technical information about the panel:
Brand: CSOT
Model: ST2751A01-8
Type: a-Si TFT-LCD, CELL
Diagonal size: 27.5 inch
Resolution: 1366x768, WXGA
Display Mode: HVA, Normally Black, Transmissive
Active Area: 607.528x345.024 mm
Surface: Antiglare (Haze 2%), Hard coating (3H)
Glass Depth: 0.50 + 0.50 mm
Transmissivity: 7.2% (with Polarizer)
Contrast Ratio: 3000: 1
Display Colors: 16.7M (8-bit), CIE1931 62%
Response Time: 6.5 (G to G)
Frequency: 60Hz
Signal Interface: LVDS (1 ch, 8-bit), 30 pins
Voltage: 12.0V
PWM SMPS in SOT-23-6, SOT-26, TSOP-6 packages
In
the circuitry of modern switching power supplies (SMPS), PWM
controllers made in small-sized planar packages with six terminals have
gained wide popularity. The enclosure type designation can be SOT-23-6,
SOT-23-6L, SOT-26, TSOP-6, SSOT-6. The appearance and arrangement of the
pins are shown in the figure below. In this case, the code marking
LD7530A is shown on the left fragment of the picture.
Pin assignment:
1 - GND. (Common wire).
2
- FB. (FeedBack - Feedback). Input for controlling the duration of
pulses with a signal from the output voltage. Sometimes it can be
labeled COMP (input comparator).
3 - RI / RT / CT / COMP / NC -
Depending on the type of microcircuit, it can be used for a
frequency-setting RC circuit (RI / RT / CT), or for organizing
protection, as an input of a PWM trip comparator at a threshold value at
its input, specified in the document. In some types of microcircuits,
this input may not be used in any way (NC - No Connect).
4 - SENSE, otherwise CS (Current Sense) - Input from the current sensor at the source of the key.
5 - VCC - Input voltage supply and start of the microcircuit.
6 - OUT (GATE) - Output for controlling the gate (Gate) of the key.
Functionally,
these regulators work on the principle of the previously popular xx384x
PWM microcircuits, which have proven themselves well in terms of
reliability and stability.
Some difficulties often arise when
replacing or choosing an analog for such PWM regulators due to the use
of code markings in the designation of the type of microcircuits. The
situation is complicated by a large number of component manufacturers
who do not always provide documentation to the mass access, just as not
all manufacturers of finished devices supply repair service centers with
diagrams, so repairmen often have to study real circuit solutions by
installed components and wiring connections directly on the board.
In
practice, PWM microcircuits and the marking code EAxxx and Eaxxx are
often found. Official documentation for them was not found in the public
domain, but discussions on the forums and pieces of pictures from PDF
from System General, which publishes them as SG6848T and SG6848T2, have
survived. The drawing is here placed left .
For the attention of the masters, here below are PDF datasheet tables
compiled from information available on the Internet and PDF documents
for the selection of analogues types when replacing the most common
six-legged planar PWM with pinout pins: pin1 - GND, pin2 - FB (COMP),
pin4 - Sense, pin5 - Vcc, pin6 - OUT ...
Their main difference is the application and purpose of pin 3.
| Name | Part Number | Fabricant | Marking |
|---|---|---|---|
| SG6849 | SG684965TZ | Fairchild / ON Semi | BBxx |
| SG6849 | SG6849-65T, SG6849-65TZ | System General | MBxx EBxx |
| SGP400 | SGP400TZ | System General | AAKxx |
PWM controllers (PWM) with a 95-100 kOhm resistor on pin 3.
When
applying the PWM listed below, the frequency should be set with the RT
(RI) resistor from pin 3 to ground. Usually its nominal value is chosen
95-100 kOhm for a frequency of 65-100 KHz. For more details, see the
here below attached documentation. PDF files are packed in RAR.
| Name | Part Number | Fabricant | Marking |
|---|---|---|---|
| AP3103A | AP3103AKTR-G1 | Diodes Incorporated | GHL |
| AP8263 | AP8263E6R, A8263E6VR | AiT Semiconductor | S1xx |
| AT3263 | AT3263S6 | ATC Technology | 3263 |
| CR6848 | CR6848S | Chip-Rail | 848H16 |
| CR6850 | CR6850S | Chip-Rail | 850xx |
| CR6851 | CR6851S | Chip-Rail | 851xx |
| FAN6602R | FAN6602RM6X | Fairchild / ON Semi | ACCxx |
| FS6830 | FS6830 | FirstSemi | |
| GR8830 | GR8830CG | Grenergy | 30xx |
| GR8836 | GR8836C, GR8836CG | Grenergy | 36xx |
| H6849 | H6849NF | HI-SINCERITY | |
| H6850 | H6850NF | HI-SINCERITY | |
| HT2263 | HT2263MP | HOT-CHIP | 63xxx |
| KP201 | Kiwi Instruments | ||
| LD5530 | LD5530GL LD5530R | Leadtrand | xxt30 xxt30R |
| LD7531 | LD7531GL, LD7531PL | Leadtrend | xxP31 |
| LD7531A | LD7531AGL | Leadtrend | xxP31A |
| LD7535/A | LD7535BL, LD7535GL, LD7535ABL, LD7535AGL | Leadtrend | xxP35-xxx35A |
| LD7550 | LD7550BL, LD7550IL | Leadtrend | xxP50 |
| LD7550B | LD7550BBL, LD7550BIL | Leadtrend | xxP50B |
| LD7551 | LD7551BL/IL | Leadtrend | xxP51 |
| LD7551C | LD7551CGL | Leadtrend | xxP51C |
| NX1049 | XN1049TP | Xian-Innuovo | 49xxx |
| OB2262 | OB2262MP | On-Bright-Electronics | 62xx |
| OB2263 | OB2263MP | On-Bright-Electronics | 63xx |
| PT4201 | PT4201E23F | Powtech | 4201 |
| R7731 | R7731GE/PE | Richtek | 0Q= |
| R7731A | R7731AGE | Richtek | IDP=xx |
| SD4870 | SD4870TR | Silan Microelectronics | 4870 |
| SF1530 | SF1530LGT | SiFirst | 30xxx |
| SG5701 | SG5701TZ | System General | AAExx |
| SG6848 | SG6848T, SG6848T1, SG6848TZ1, SG6848T2 | Fairchild / ON Semi | AAHxx EAxxx |
| SG6858 | SG6858TZ | Fairchild / ON Semi | AAIxx |
| SG6859A | SG6859ATZ, SG6859ATY | Fairchild / ON Semi | AAJFxx |
| SG6859 | SG6859TZ | Fairchild / ON Semi | AAJMxx |
| SG6860 | SG6860TY | Fairchild | AAQxx |
| SP6850 | SP6850S26RG | Sporton Lab | 850xx |
| SP6853 | SP6853S26RGB, SP6853S26RG | Sporton Lab | 853xx |
| SW2263 | SW2263MP | SamWin | |
| UC3863/G | UC3863G-AG6-R | Unisonic Technologies Co | U863 U863G |
| XN1049 | XN1049, XN1049TP | Innuovo Microelectronics | 49 xxx |
PWM controllers that use pin 3 differently.
When
using the following PWM (PWM controllers), you should pay attention to
pin 3, which can be used to organize protection - thermal or from
overvoltage of the input voltage.
The frequency can be fixed at 65kHz, or set by the value of the capacitor at pin 3.
When replacing any microcircuits with analogs, carefully study the documentation. PDF files are packed in a RAR archive.
| Name | Part Number | Fabricant | Marking |
|---|---|---|---|
| AP3105/V/L/R | AP3105KTR-G1, AP3105VKTR-G1, AP3105LKTR-G1, AP3105RKTR-G1 | Diodes Incorporated | GHN GHO GHP GHQ |
| AP3105NA/NV/NL/NR | AP3105NAKTR-G1, AP3105NVKTR-G1, AP3105NLKTR-G1, AP3105NRKTR-G1 | Diodes Incorporated | GKN GKO GKP GKQ |
| AP3125A/V/L/R | AP3125AKTR-G1, AP3125VKTR-G1, AP3125LKTR-G1, AP3125RKTR-G1 | Diodes Incorporated | GLS GLU GNB GNC |
| AP3125B | AP3125BKTR-G1 | Diodes Incorporated | GLV |
| AP3125HA/HB | AP3125HAKTR-G1, AP3125HBKTR-G1 | Diodes Incorporated | GNP GNQ |
| AP31261 | AP31261KTR-G1 | Diodes Incorporated | GPE |
| AP3127/H | AP3127KTR-G1, AP3127HKTR-G1 | Diodes Incorporated | GPH GSH |
| AP3301 | AP3301K6TR-G1 | Diodes Incorporated | GTC |
| FAN6862 | FAN6862TY | Fairchild / ON Semi | ABDxx |
| FAN6863 | FAN6863TY, FAN6863LTY, FAN6863RTY | Fairchild / ON Semi | ABRxx |
| HT2273 | HT2273TP | HOT-CHIP | 73xxx |
| LD7510/J | LD7510GL, LD7510JGL | Leadtrend | xxP10 xxP10J |
| LD7530/A | LD7530PL, LD7530GL, LD7530APL, LD7530AGL | Leadtrend | xxP30 xxxP30A |
| LD7532 | LD7532GL | Leadtrend | xxP32 |
| LD7532A | LD7532AGL | Leadtrend | xxP32A |
| LD7532H | LD7532HGL | Leadtrend | xxP32H |
| LD7533 | LD7533GL | Leadtrend | xxP33 |
| LD7536 | LD7536GL | Leadtrend | xxP36 |
| LD7536R | LD7536RGL | Leadtrend | xxP36R |
| LD7537R | LD7537RGL | Leadtrend | xxP37R |
| LD7539C GL | LD7539C GL | Leadtrend | xxP39C |
| ME8204 | ME8204M6G | MicrOne | ME8204xx |
| NCP1250 | NCP1250ASN65T1G, NCP1250BSN65T1G, NCP1250ASN100T1G, NCP1250BSN100T1G | ON Semiconductor | 25xxxx |
| NCP1251 | NCP1251ASN65T1G, NCP1251BSN65T1G, NCP1251ASN100T1G, NCP1251BSN100T1G | ON Semiconductor | 5xxxxx |
| OB2273 | OB2273MP | On-Bright-Electronics | 73xx |
| R7735 | R7735AGE, R7735HGE, R7735GGE, R7735RGE, R7735LGE | Richtek | |
| UC3873/G | UC3873-AG6-R, UC3873G-AG6-R | Unisonic Technologies | U873 U873G |
LED TV BBK 28LEM-1044 / T2C with LCD ST2751A01-8, diagonal size 27.5 "(70 cm) 16: 9. The required brightness of the screen of 200 cd / m2 is provided by LED backlighting. The ratio of maximum brightness to minimum ( contrast) is 3000: 1. The display technology of the model is implemented with LED backlighting.
ST2751A01-8 sensor and CV512H-U42 motherboard software provide high quality HD viewing at 1366x768 pixels in 720p (HD Ready). Supported media file formats: MP3, MPEG4, HEVC (H.265), MKV, JPEG.
The power of the acoustic system of sound is 10 W (2x5 W), 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, component, VGA, HDMI x3, 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 TV can use a power supply unit as part of the MainBoard.
Dimensions: with stand 643x418x137 mm, without stand 643x393x86 mm.
TV weight: 3.1 kg.
Attention! The ST2751A01-8 panel of the BBK 28LEM-1044 / T2C LED TV is an expensive and unreliable element.
Do not allow any impact 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 unrepairable.