Samsung UE40JU600K strange Backlight issue

[Bloopeta]

I got a Samsung UE40JU600K the other week and was told it needed backlights. I stripped it down, and tested backlights and there were a number of LEDs not working. I ordered a complete new backlight array, which arrived yesterday, fitted, switched on and all seemed fine, so reassembled TV, swithched on, and no backlights!
Stripped down again, checked and backlights were fine, so started reassembly again, and it appears that once screen is connected up, the backlights dont work!

Never came across this issue before, any help grately appreciated.

[neilc6]

Re: Samsung UE40JU600K strange Backlight issue

Bad backlights can damage the power supply on Samsungs due to the lack of protection shutdown. I would check the power diode in that section and the switching FET.

[Bloopeta]

Re: Samsung UE40JU600K strange Backlight issue

Bad backlights can damage the power supply on Samsungs due to the lack of protection shutdown. I would check the power diode in that section and the switching FET.

Thanks for getting back to me, I wasnt aware of this. I will check the diode, which it is switching FET. please?

[RDC55]

Re: Samsung UE40JU600K strange Backlight issue

Posting picture of the entire back side is helpful, I searched but could not determine if this model has a TCON.

If so, disconnect one of the TCON output ribbon cables one at a time and see if the set powers up OK with video on one side.

Samsung made it easy to test the power supply / backlights. Simply disconnect one end of the cable that goes from the power supply to the main board and plug the TV in. The backlights should illuminate if the power supply and backlights are OK.

[Bloopeta]

Re: Samsung UE40JU600K strange Backlight issue

Posting picture of the entire back side is helpful, I searched but could not determine if this model has a TCON.

If so, disconnect one of the TCON output ribbon cables one at a time and see if the set powers up OK with video on one side.

Samsung made it easy to test the power supply / backlights. Simply disconnect one end of the cable that goes from the power supply to the main board and plug the TV in. The backlights should illuminate if the power supply and backlights are OK.

Here is a pic of complete back.

So when cable from power board to main board is unplugged, backlights work.

When I unplug either of the Tcon output ribbon cables, the backlights work, but there is no video

If I leave everything plugged in and connected up as should be, I get no backlights

[RDC55]

Re: Samsung UE40JU600K strange Backlight issue

Well, that could be a panel or panel buffer board loading things down. Look for fuses on the TCON and compare power with cables connected and not. I still can't find that model number TV so I can't be more specific.

You also have access to the panel buffer boards, check across a few of the MLCC caps and verify no shorts are present.

Is the title correct on model number?

Does the screen turn solid bright white with the ribbon cables off?

That version of TCON usually has some status LED's also, report back on how those are behaving with cables on or off.

[Bloopeta]

Re: Samsung UE40JU600K strange Backlight issue

Well, that could be a panel or panel buffer board loading things down. Look for fuses on the TCON and compare power with cables connected and not. I still can't find that model number TV so I can't be more specific.

You also have access to the panel buffer boards, check across a few of the MLCC caps and verify no shorts are present.

Is the title correct on model number?

Does the screen turn solid bright white with the ribbon cables off?

That version of TCON usually has some status LED's also, report back on how those are behaving with cables on or off.

Here are pics of model no. And some of Tcon with various cables connected to show status light.

Fuse on Tcon reads 12.3 with cables unplugged, and 12.7 with cables connected

The status LED lights blue with either or both cables disconnected. With all cables connected it only comes on for a second when TV is first turned on.

How do I check across a few of the MLCC caps and verify no shorts are present please?

[RDC55]

Re: Samsung UE40JU600K strange Backlight issue

"How do I check across a few of the MLCC caps and verify no shorts are present please?"

Picture attached -the small rectangular capacitors are MLCC capacitors. One end usually ties to chassis and the other to a voltage produced by the TCON. With everything hooked up one side of the cap should ohm to chassis ground and the other should not. Most of them are in parallel so usually no need to check every one if the readings are OK.

"The status LED lights blue with either or both cables disconnected. With all cables connected it only comes on for a second when TV is first turned on."

I was referring to status LED's on the TCON itself, although that is good info on the power status LED.

[Bloopeta]

Re: Samsung UE40JU600K strange Backlight issue

I was referring to status LED's on the TCON itself, although that is good info on the power status LED.

It is the status LED on the Tcon itself that Ive reported on, the blue one on the right hand side of Tcon in the pictures

[neilc6]

Re: Samsung UE40JU600K strange Backlight issue

Based on your test results, I would try replacing the tcon board.

[RDC55]

Re: Samsung UE40JU600K strange Backlight issue

OK, I see that now. How about the other LED that looks like it is for the 3.3 V, does it ever illuminate like with both cables disconnected? QP301 just to the left of the one you show illuminated.

In the 3rd picture there is no blue LED because you removed the ribbon from the main, which is where power from the TCON comes from.

[RDC55]

Re: Samsung UE40JU600K strange Backlight issue

I agree a TCON is worth a try particularly if that other status light is never illuminating, and they are not very expensive.

[Bloopeta]

Re: Samsung UE40JU600K strange Backlight issue

OK, I see that now. How about the other LED that looks like it is for the 3.3 V, does it ever illuminate like with both cables disconnected? QP301 just to the left of the one you show illuminated.

In the 3rd picture there is no blue LED because you removed the ribbon from the main, which is where power from the TCON comes from.

The other status light OP301 never illuminates, whether cables are connected or not.

The blue OP300 only illuminates when one or more cables are disconnected. When all cables are connected, it only illuminates for a brief second when TV is first powered on.


The caps on driver boards you asked me to check, eith meter on ohms, I get ground one sidre and a reading off 320 - 325 with everything connected and TV powered on

[Bloopeta]

Re: Samsung UE40JU600K strange Backlight issue

Based on your test results, I would try replacing the tcon board.

I will order one up

[Bloopeta]

Re: Samsung UE40JU600K strange Backlight issue

I agree a TCON is worth a try particularly if that other status light is never illuminating, and they are not very expensive.

I will order one and see how I get on

[Bloopeta]

Re: Samsung UE40JU600K strange Backlight issue

So, new Tcon arrived today, tried it, heard a click when turned TV on and burning smell. Checked power board and Im getting beep instead of reading (circled)

[RDC55]

Re: Samsung UE40JU600K strange Backlight issue

If by beep you mean virtually zero ohms you can trace that diode out and see if it ties to a transformer, which would explain the low reading. You would need to load high resolution pics of the front and back of the power supply to get help on that - Otherwise, you could just lift one end and test it.

If you are not sure where the burning smell came from I might suggest starting back at square one and evaluating the power supply and LED's as a standalone unit not connected to the Main or TCON. And a word of caution have the power source easily removable and safety glasses if you stick your face in there.

[Bloopeta]

Re: Samsung UE40JU600K strange Backlight issue

If by beep you mean virtually zero ohms you can trace that diode out and see if it ties to a transformer, which would explain the low reading. You would need to load high resolution pics of the front and back of the power supply to get help on that - Otherwise, you could just lift one end and test it.

If you are not sure where the burning smell came from I might suggest starting back at square one and evaluating the power supply and LED's as a standalone unit not connected to the Main or TCON. And a word of caution have the power source easily removable and safety glasses if you stick your face in there.

Going back to basics, with power and LEDS as standalone, the backlights work.

When everything is connceted, no backlights and no lights on Tcon board.

If I unplug either of the ribbons from Tcon to screen, backlights work, and blue light (OP300) on Tcon illuminates

[RDC55]

Re: Samsung UE40JU600K strange Backlight issue

The caps on driver boards you asked me to check, eith meter on ohms, I get ground one sidre and a reading off 320 - 325 with everything connected and TV powered on

This should be done with all power removed from the TV - never do a resistance check on a live circuit.

Other than the above I am kind of out of ideas. The burnt smell may have been the new TCON? Perhaps others will have more ideas, but with the backlights going off with the panel connected and the TCON replaced it would seem to point to a defect within the panel.

[vinceroger69]

Re: Samsung UE40JU600K strange Backlight issue

on the lcd panel pcb are there any burnt componets?