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50″ LED TV Display Problem Repaired
Hello everyone, this is my first participation in Jestine Yong’s blog. The TV subject to this participation is mine, I bought it more three years and it is out of warranty. The brand is MGS and the reference is ELED 50FHD MHDV341.
It’s been more than three months that when turning the TV ON we hear the sound but no picture, we are forced to turn Off and On the TV three or four times to have the image.
Last Friday I cannot have neither the image nor the sound even I switched it On & Off thirty times, so I decide to open the set to try to repair it. A first visual check of all the PCBs did not show anything abnormal. All the voltages delivered by the power supply PCB are presents, so I suspected the 5 capacitors of 100v 100μF in the inverter board that I changed by new ones but without any result.
For information the 12v voltage (LVDS power) and the 5v voltage (LEDs inverter ON) are delivered only after turning on the TV (switch from Standby mode to on mode).
The back light of the set is controlled by the main board T.MSD309.B81C 12176 which sends a 5v signal (On) to the LEDs inverter board.
Normally, after turning the TV on, it is necessary to wait 7 seconds till the splash screen with MGS logo appear and 15s to have the video image.
So I removed the cable coming from main board to control the inverter and I injected a 5v to pin 12 of CN1 on the LEDs inverter, the screen turns on but without any video image, after verifications and controls I found that the LVDS card that managing the T-con is the cause of blocking the video image.
I then disconnected the 12v power cable of the LVDS card and I restarted the TV, the 12v connector is plugged to its place in LVDS board after 15s of turning TV ON and at my surprise the video image is back again.
So to solve the problem I had the idea to build and install a timer that blocks the 12v and 5v voltages powering up respectively the LVDS and the LED inverter boards during the first 15 seconds after starting the TV, to do so I created a simple circuit based on the 2N2222 transistor and a 2 relays card that I had bought, three months ago from Aliexpress at 2.63USD. The circuit is powered by 12v external power supply and controlled by standby red LED powering voltage (1.7v).
In standby mode the 1.7v power supply (red LED on) saturates the base of T1 (2N2222 NPN) across the resistor R1 to drive the negative voltage which charges the two 16v1500μF capacitors and excites the 2 relays, the control voltages 5v and 12v are connected to the NC contacts of the relays.
After switching on the TV -the red LED goes Off and the green LED goes On- the relay card is kept in function by the energy stored in the 2 capacitors for a time of 15 seconds needed by the set to display the video image.
I had to buy the main and the LVDS boards for about 100 USD and wait at least 30days to get them, but my TV returned back to life without changing any PCB and spending only 2.63 USD of the relay PCB that I had bought 3 months ago.
This article was prepared by Mr Bouhraoui Mohamed from Casablanca Morocco who was working for 20 years in a company specialized in audio-visual (Panasonic, Nec, JVC, Polycom, Polaroid) and photography (Olympus, Polaroid, Noritsu, San marco, KIS), currently he is the technical manager in airport runway lighting company for 13 years.
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