Emerson LC401EM3F No power - Please Help

[Shane711]

Re: Emerson LC401EM3F No power - Please Help

OK, so then the diodes are not the problem. The board turns on, the TV turns on, I have sound and video.

So all my voltages look good except the 24V going to the backlights. I am only getting 19V and when I unplug the wire I get 22V

[JohnCT]

Re: Emerson LC401EM3F No power - Please Help

OK, so then the diodes are not the problem. The board turns on, the TV turns on, I have sound and video.

So all my voltages look good except the 24V going to the backlights. I am only getting 19V and when I unplug the wire I get 22V

Sometimes the actual run voltage on any given connector may not match the printed call out on the board.

If you have a board that works, then compare the voltages.

If your 24V is indeed low, that will cause backlight flutter. Before you investigate the 24V line, check the pfc voltage against your known good board. If your good board reads the same as the the troubled board, then head towards the 24v line.

A quick way of seeing if any of your bypass electros are bad is to heat them up with a hair dryer and monitor the voltage. If the voltage climbs towards normal, check the ESR of the 24V bypass caps. If the caps are good, you have to investigate the feedback line - could be a separate winding on the full run transformer of it might use an opto coupler from the secondary to the primary. A schematic will be helpful at this point.

John

[Shane711]

Re: Emerson LC401EM3F No power - Please Help

I did not have a board that worked so I bought a broken one off eBay, fixed it and now that board works. I am getting 23.6 volts going to the backlights and it works perfect. So now I think I am going to try and fix these other boards by swapping out parts until I find the bad part, that should tell me if it is a bad transformer.

[JohnCT]

Re: Emerson LC401EM3F No power - Please Help

I did not have a board that worked so I bought a broken one off eBay, fixed it and now that board works. I am getting 23.6 volts going to the backlights and it works perfect. So now I think I am going to try and fix these other boards by swapping out parts until I find the bad part, that should tell me if it is a bad transformer.

Transformer failure these days is extraordinarily rare.

The first thing to check is the pfc voltage across the big electro. If the failed board is reading more than a couple of volts lower than the good board, investigate the pfc circuit (or even the cap itself).

Did you try heating the board?

John

[Shane711]

Re: Emerson LC401EM3F No power - Please Help

So the good board has less pfc voltage 334 volts and it fluctuates from 332 to 335. But I also have a better main capacitor on the bad board.

Heating the board makes the TV want to turn off and does not effect the backlights flickering.

[Shane711]

Re: Emerson LC401EM3F No power - Please Help

I found a bad 47K resistor on the bottom of the board, R1716. I replaced it but it did not fix the problem. I will look for more tomorrow.