Samsung UN40F5500AF No back light

[ny_jets_head]

Everything else works.

I have heard that the LEDs blow and cause this.

I checked the power supply and found that the voltages for the LED'S on the caps 9218 and 9118 are bouncing around from 306 to 290V on my VOM which is strange. This sound like an issue exists on the PS board

Looking for advise before I crack the walnut open to check the LEDs themselves

Thanks

[6BW6]

Re: Samsung UN40F5500AF No back light

Not sure of the circuit off hand for this model

If the LED voltage are 'bouncing' the supply could be starting up and shutting down, this voltage is usually pulse width modulated (to allow brightness setting).
I doubt the PWM frequency will be low enough to make the voltage 'bounce', it may well be in trip mode because of a faulty LED or two..... or faulty rectifiers.

Before stripping down I'd be checking the rectifier diodes at least. Backlight strips and LEDs are available should they be needed.

Dave

[budm]

Re: Samsung UN40F5500AF No back light

You have two Boost converter circuits (Q9101, 9201, Inductors T9101, 9201) and those two caps are filter caps for each boost converter output. The PWM controlled MOSFETs (Q9102, Q9202) are on the Cathode return side of the LED strings.
What is the Voltage rating on those two caps? You measure the Voltage right between the two legs of the caps? Same reading if you do not have the LED connector in place? Right now it looks like you have no load on the LED connectors.
The batteries for your meter is good?

Samsung BN44-00645A (KTL SU10054-XXXX) Power Supply / LED Board
http://www.shopjimmy.com/samsung-bn4...pply-unit.htm#

[ReeceyBurger123]

Re: Samsung UN40F5500AF No back light

If your return voltage isnt correct, you should check this out:

https://www.badcaps.net/forum/showthread.php?t=52928

[ny_jets_head]

Re: Samsung UN40F5500AF No back light

You have two Boost converter circuits (Q9101, 9201, Inductors T9101, 9201) and those two caps are filter caps for each boost converter output. The PWM controlled MOSFETs (Q9102, Q9202) are on the Cathode return side of the LED strings.
What is the Voltage rating on those two caps? You measure the Voltage right between the two legs of the caps? Same reading if you do not have the LED connector in place? Right now it looks like you have no load on the LED connectors.
The batteries for your meter is good?

Samsung BN44-00645A (KTL SU10054-XXXX) Power Supply / LED Board
http://www.shopjimmy.com/samsung-bn4...pply-unit.htm#

Thanks to all for the suggestions!

I checked the diodes and they are fine.

My fluke has a good battery in it so the voltages readings are accurate.

I'm going to open up the panel I suspect that is where the problem lies
The voltages read the same with the panel disconnected. Based on the threads I have read the circuit must be looking for a load from the LEDs

Besides the obvious burned out LED has anyone found out what voltage and where you power the individual LED strips?

Judging from the high voltage at the driver these boys must be in series.

[Kilroys]

Re: Samsung UN40F5500AF No back light

If the LED backlights do not illuminate,
disconnect the cable between the Main Board and the SMPS.

Perhaps this could help you.

[ReeceyBurger123]

Re: Samsung UN40F5500AF No back light

Thanks to all for the suggestions!

I checked the diodes and they are fine.

My fluke has a good battery in it so the voltages readings are accurate.

I'm going to open up the panel I suspect that is where the problem lies
The voltages read the same with the panel disconnected. Based on the threads I have read the circuit must be looking for a load from the LEDs

Besides the obvious burned out LED has anyone found out what voltage and where you power the individual LED strips?

Judging from the high voltage at the driver these boys must be in series.

Read the thread that I linked.

[ny_jets_head]

Re: Samsung UN40F5500AF No back light

Read the thread that I linked.

Thanks! I did read it and checked out all the stuff posted as well, the assistance here is fabulous!

Well after determining that it must be the panel, I cracked it open and yes I have two bad LED's both in the same location but on different strips.

Also taken out on the strip is what I think based on the markings on the SMD Its a 3V Zener diode based on my research.

The markings are 4E D8 its a SOD 123 device. (pic included) If I'm wrong here please let me know...

I'm going to try to fix the strips, I have had reasonable success using hot air in the past on stuff like this.

What I need help with is the LED device replacement.
I assume they are 3V LEDs The color temp is blueish

Advice would be great!

The part number on the strip is 2013SVS40F L8 REV 1.8
The strips are two piece, the part number is for the left half that plugs into the buss in in panel

I was able to functionally test the right side of the strip with a 24V supply voltage which is what the strip is marked with.
But I have not had any luck with firing up the Left half.

One more worry is why did they fail?.. The PS could still have issues I will deal with that once I get the strips ready.

[Boiko]

Re: Samsung UN40F5500AF No back light

...The markings are 4E D8 its a SOD 123 device...

I have similar problem with my strip 2013SVS40F L8 REV 1.8 on TV UE40F6670SS. I think this element is not zener diode. Probably this is suppressor for 24V. I measure 7-8V on this suppressor in normal light strip.
Sorry, my english is ...

[ny_jets_head]

Re: Samsung UN40F5500AF No back light

I put this TV a side and now have time to fix it.

Please help me identify exactly what this component is so I can order it.

What is the device you used to replace the 4E D8 SMD device located at the top of the LED strip. as show in the previous post


Also:
Are the LEDs 3.3 Volt? does anyone have a part number for them

I need to replace a few of them as well thanks!

[vinceroger69]

Re: Samsung UN40F5500AF No back light

maybe these? for replacements
https://ru.aliexpress.com/item/100pc...7-e5958206df4f

[ny_jets_head]

Re: Samsung UN40F5500AF No back light

Thanks!

I will check them out and compare to the existing LED

[vinceroger69]

Re: Samsung UN40F5500AF No back light

as your in the usa try shopjimmy i see there doing led kits now i think you get 12 with reflectors at a good price and may save waiting too long for delivery.


Edit its this kit if there 3v leds and roughly the same size led this kit may work
https://www.shopjimmy.com/replacemen...-set-of-12.htm

[ny_jets_head]

Re: Samsung UN40F5500AF No back light

Thanks will check that out as well.
I have a flat iron I use to remove and replace them, works well.

[ny_jets_head]

Re: Samsung UN40F5500AF No back light

OK LEDS are installed but I'm still having trouble identifying the components on the end of the strip that are burned.

I also feel I should replace both devices, the first one is marked with 2F
the second one is connected to the other in series is marked with 4E

Photo show the two.

Thanks

[vinceroger69]

Re: Samsung UN40F5500AF No back light

http://www.s-manuals.com/smd/4e
http://www.s-manuals.com/smd/2f

not sure what the 2f part is if sod 123

https://cdn.badcaps-static.com/pdfs/...66be3d5a35.pdf

[ny_jets_head]

Re: Samsung UN40F5500AF No back light

Thanks for the reply.

It appears we both were using the same resources

The 4E may be the correct device.

But the 2F is also an SOD 123 package so that is where I have the problem.

I also had a reply stating that the device is not a zener diode but I think it might be.
It has to be a diode, it is not a fuse, a resistor or active component.

[vinceroger69]

Re: Samsung UN40F5500AF No back light

maybe budm has a idea what the parts are ?

[ny_jets_head]

Re: Samsung UN40F5500AF No back light

Update:

Removed the 4E Diodes and reinstalled the repaired strips and they worked!

They must be part of a protection circuit.

Putting it back together!

[Louis82]

Re: Samsung UN40F5500AF No back light

Same tv here. All voltages are bouncing. Big filter cap from 280v to 396v, LED driver connector pins measure 156v to 192v bouncing. I checked voltages with the board off the tv and same bouncing readings. I though I migh had def LED's. I took screen apart and all LED's are fine.

One thing I notice is that 3 LED strips are quickly flashing. I believe this is because voltages reach a high peak and the go low again.

Any suggestions of what to check on power board?

Thank you