Mulja tv repair portal
Equipment Repairs => LCD TV forum => Topic started by: harvey on August 27, 2017,14:56:26
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Hi Good Fellows, This LCD red LED flashing. No picture. I have checked the power supply board all the rails seem ok. Could the fault be on the inverter section of the board? I shall be grateful for your help. Regards
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Hi Harvey,
Disconnect the harness between the power supply and main boards. Plug the tv into the mains. If it turns on with backlights, then the main board is faulty.
If it doesn't, and you're convinced the power supply is OK, then you may have faulty LEDs in the panel. The D series seems notorious for this.
Bruce
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Thanks for the reply. I will follow it what you said. Regards
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Hi, Gentlemen! After disconnecting the harness originally there was no light on the screen. I re-solder random joints on the board and tried it again. Now the screen lights up by disconnecting the harness. But with the harness connected screen still dark and red light flashing. As you say it could be the main video board then. Is it repairable or shall I put the telly under the front tyre of my car. Your opinion much appreciated. Regards
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Hi Harvey,
Yep, definitely main board, possibly not supplying INV=ON to the PSU. At this point I quote the customer for a main board and see what plays out.
Bruce
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Hi Downunder, Thanks for the reply. Could you please explain what you mean by "mainboard possibly not supplying INV=ON to the PSU" Just out of curiosity to know.
Regards
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One of the functions of the main board is to supply a PS-ON voltage of around 3V to activate the power supply which then generates voltages other than standby volts to operate the TV. In like fashion, it also supplies a BL-ON (INV-ON) signal to the power supply to activate the backlight LEDs, also of the order of 3V. These can be measured at the power supply plug that connects to the main board. Samsung uses hold-up resistors on the power supply which allow the backlights to turn on when the main board is unplugged. That means that the power supply and backlights are functional, but the main board isn't doing its job. Hope that clears it up.
Bruce
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Thanks Downunder for the precise explanation of how the main board works. Much appreciated. Regards
harvey