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post #1 of 16 Old 07-10-2014, 06:39 PM - Thread Starter
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Exclamation Samsung LN46D550K1FXZA

All electrolytics on power board replaced, most with higher voltage.

With red LED in lower right corner, I turn on the tv. It flashes several times and I see the Samsung logo appears momentarily and the sound comes on. Can't remember if red led is suppose to be on.

On the left side of TV is a long narrow board with about 6 LEDs with none lite. They should be on.
Once and a while I can get the TV on and works normal until shut off. It doesn't come again.

If any one has a schematic I would like appreciate a copy. Any voltages also. I was in TV repair 25 years ago.

Thanks to all who help.

Last edited by rob68; 07-10-2014 at 06:40 PM. Reason: clarity.
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post #2 of 16 Old 07-10-2014, 07:47 PM
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It sounds like the Tv is coming on and staying on? right? it's not clicking off?

If you see something on the screen (samsung logo) momentarily then it goes away, it could be bad backlights or power/inverter board problem. If it's backlights then that is serious (cracking open the lcd display panel to replace backlights is not something Tv repair shops even do).

If you connect a signal, turn on Tv, then after it goes out, shine a flashlight into the front of the screen, can you make out evidence of picture in there? Move the light around different areas, bring up tv menu or volume osd...

Might be able to check some DC voltages. This model had a few different panel versions, so different board layout. If you can post some large high quality photos of the back of the Tv showing the board layout then maybe can help further.
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post #3 of 16 Old 07-11-2014, 07:13 AM - Thread Starter
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Cool

Quote:
Originally Posted by hammerdwn View Post
It sounds like the Tv is coming on and staying on? right? it's not clicking off?

If you see something on the screen (samsung logo) momentarily then it goes away, it could be bad backlights or power/inverter board problem. If it's backlights then that is serious (cracking open the lcd display panel to replace backlights is not something Tv repair shops even do).

If you connect a signal, turn on Tv, then after it goes out, shine a flashlight into the front of the screen, can you make out evidence of picture in there? Move the light around different areas, bring up tv menu or volume osd...

Might be able to check some DC voltages. This model had a few different panel versions, so different board layout. If you can post some large high quality photos of the back of the Tv showing the board layout then maybe can help further.
Yes TV stays on. No relay click. The flashlight did not reveal anything, even on another working TV. I forgot to mention the narrow board along the left-front. When the TV works, all the LEDs are on. They are now off.

Let me know if pictures are ok. Batteries died in camera.
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post #4 of 16 Old 07-11-2014, 07:27 AM
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Using a flashlight on a working Tv? maybe you misunderstood. That is a test to use when the backlights are dropping out. So when the picture goes out, can you tell if the back lights are still on? If you put the Tv in a dark room, wait for it to "fail", is the panel still glowing? you can see it from the front in a dark room or maybe from the back through "holes" in the back of the panel...

I think on this model, there is also a way to force the back lights on:
Unplug the power cord.
Disconnect the wiring harness that goes from the Main board (board with av inputs) to the power supply board.
Plug in the power cord (you may have to press power button if it doesn't come on).
The backlights should come on. Can you see that happen? Do the back lights stay on or flicker and drop out?
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post #5 of 16 Old 07-11-2014, 07:51 AM
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You can also measure the DC voltages on the power supply board (re-connect any wiring harnesses you have disconnected).
Connector CN1801 (top right corner of power board).
Black meter lead to chasis ground.
Red meter lead to each pin of CN1801 (don't short pins together).
Set meter 50vdc.
Plug in tv power cord (press power button if needed).
Watch meter as Tv comes on.
Do you get 13v on pin 11?
Does it stay up or drop out?

There could be bad capacitors on the Inverter board(s). Those are under the plastic cover on the far right edge/side of back of panel.
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post #6 of 16 Old 07-11-2014, 11:44 AM - Thread Starter
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Quote:
Originally Posted by hammerdwn View Post
You can also measure the DC voltages on the power supply board (re-connect any wiring harnesses you have disconnected).
Connector CN1801 (top right corner of power board).
Black meter lead to chasis ground.
Red meter lead to each pin of CN1801 (don't short pins together).
Set meter 50vdc.
Plug in tv power cord (press power button if needed).
Watch meter as Tv comes on.
Do you get 13v on pin 11?
Does it stay up or drop out?

Thanks for helping.

There could be bad capacitors on the Inverter board(s). Those are under the plastic cover on the far right edge/side of back of panel.
Once in awhile the sound and picture both would be off, like now. From the back of TV. I can see the back-light come on and go off.
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post #7 of 16 Old 07-11-2014, 12:03 PM
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Do you get 13v on pin 11 CN1801 after back lights drop out?

Did forcing procedure work?

Unplug the power cord.
Disconnect the wiring harness that goes from the Main board (board with av inputs) to the power supply board.
Plug in the power cord (you may have to press power button if it doesn't come on).
The backlights should come on. Can you see that happen? Do the back lights stay on or flicker and drop out?
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post #8 of 16 Old 07-11-2014, 06:32 PM - Thread Starter
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Quote:
Originally Posted by hammerdwn View Post
Do you get 13v on pin 11 CN1801 after back lights drop out?

Did forcing procedure work?

Unplug the power cord.
Disconnect the wiring harness that goes from the Main board (board with av inputs) to the power supply board.
Plug in the power cord (you may have to press power button if it doesn't come on).
The backlights should come on. Can you see that happen? Do the back lights stay on or flicker and drop out?
With cable disconnected, the power button is connected to the Main board and does nothing.
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post #9 of 16 Old 07-11-2014, 06:35 PM
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Measure the DC voltages on the power supply board (re-connect any wiring harnesses you have disconnected).
Connector CN1801 (top right corner of power board).
Black meter lead to chasis ground.
Red meter lead to pin of CN1801 (don't short pins together).
Set meter 50vdc.
Plug in tv power cord (press power button if needed).
Watch meter as Tv comes on.
Do you get 13v on pin 11?
Does Tv stay on but 13v stays up?
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post #10 of 16 Old 07-12-2014, 10:44 AM - Thread Starter
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Quote:
Originally Posted by hammerdwn View Post
Measure the DC voltages on the power supply board (re-connect any wiring harnesses you have disconnected).
Connector CN1801 (top right corner of power board).
Black meter lead to chasis ground.
Red meter lead to pin of CN1801 (don't short pins together).
Set meter 50vdc.
Plug in tv power cord (press power button if needed).
Watch meter as Tv comes on.
Do you get 13v on pin 11?
Does Tv stay on but 13v stays up?
No voltage om pin 11. Back-light does not come on at all.
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post #11 of 16 Old 07-12-2014, 03:48 PM
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Now the connector CN802 on the other side of the power board (the one that goes to the Main board)
pin 1 = 13v
pin13 =5v
?
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post #12 of 16 Old 07-13-2014, 08:27 PM - Thread Starter
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Quote:
Originally Posted by hammerdwn View Post
Now the connector CN802 on the other side of the power board (the one that goes to the Main board)
pin 1 = 13v
pin13 =5v
?
There is nothing more frustrating then a wacky meter. Here are all the measurements:
It appears there is a pinout printed on the boards.

Upon power up, the back lights flick on and then off.

CN1801 - 1 13v stays on - off when tv off
CN1801 - 13 5v

CN1802 -11 - 13v
CN1802 - 14 - 5v with TV on
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post #13 of 16 Old 07-13-2014, 08:40 PM
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Great, that rules out the Main board and Power Supply board. Two possibilities-
Inverter board
or
back lights inside the LCD Panel.

Your best (and really only) chance at fixing your Tv is buying and trying the Inverter board. If that doesn't fix then it's the back lights inside that panel and you are pretty much done for at that point. Yes, it is a $25 gamble...

>> click here to see inverter boards on eBay << $25
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post #14 of 16 Old 07-14-2014, 05:46 AM - Thread Starter
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Quote:
Originally Posted by hammerdwn View Post
Great, that rules out the Main board and Power Supply board. Two possibilities-
Inverter board
or
back lights inside the LCD Panel.

Your best (and really only) chance at fixing your Tv is buying and trying the Inverter board. If that doesn't fix then it's the back lights inside that panel and you are pretty much done for at that point. Yes, it is a $25 gamble...

>> click here to see inverter boards on eBay << $25
How would this diagnosis effect the loss of sound?
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post #15 of 16 Old 07-14-2014, 06:56 AM
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Can't speculate if there is something going on with the source since we can't see the picture. After you get the back lights to stay on then you might be able to see if the source is cutting out or ....
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post #16 of 16 Old 07-14-2014, 01:09 PM - Thread Starter
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Quote:
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Can't speculate if there is something going on with the source since we can't see the picture. After you get the back lights to stay on then you might be able to see if the source is cutting out or ....
Thanks for your diligence, hammerdwn.

Do you have any schematic or other service aids?

Perhaps someone else has some ideas.
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