Samsung UN40F5500AF No back light

[Andrew F. Ali]

Re: Samsung UN40F5500AF No back light

That seems to be a possible Main Filter cap fault or some other 'big' cap erratic.

[Louis82]

Re: Samsung UN40F5500AF No back light

Oh man I have removed about 7 capacitors (big ones) and they all test good. Suggestions?

[Louis82]

Re: Samsung UN40F5500AF No back light

In case it helps, big filter cap voltages bounce and only A5v and Ps-on have steady voltage.
A5v = 5v
PS-ON 3.3v

Help!

[Louis82]

Re: Samsung UN40F5500AF No back light

Replaced big filter cap and still the same. Also replaced a box cap that was reading lower than the 10% margin and still the same.
Anyone willing to help?
I just hate the idea of ordering a new board when I know the problem must be easy and somewhere.

Help!

[thoma]

Re: Samsung UN40F5500AF No back light

https://www.badcaps.net/forum/showth...=25810&page=14

schematic Samsung Power Supply BN44-00645A.pdf

https://www.badcaps.net/forum/showth...=25810&page=15

http://televid-sib.ru/index.php?topic=27588.0

BN44-00622B Samsung SMPS

[thoma]

Re: Samsung UN40F5500AF No back light



Wait until Get Manual appears!!SMPS Samsung BN44-00622B

[paulstef]

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.

4E is probably a bidirectional TVS (was mentioned before somewhere). I removed one from a working LED strip, they start conducting above about 32V in both directions.

[Hagis2k]

Re: Samsung UN40F5500AF No back light

Well been some time since i was online here, and i have another suggestion that
i been modifying multiple sets to make them run cooler.

I been repairing some of these too about the same model but the sets i worked on
is called ue40fxxxx

R9119 R9219 if the value of these is 0.27 change it to
0.55-0.6 it makes them run cooler and they are likely never to fail again.

Then the voltage drops from around 180V over diode d9202c over the string with 52 leds down to 164 and you can then remove the glue on the pot and lower the voltage on d9102c to around 127V that use to be around 135V before modding it.

After this you are down at roughly 3.2V on the leds as samsung use to drive them at 3.46V is in my opinion to much.

I also apply a very small dab of heatsink compund to the backside of the strip where the led is mounted, i think it is a design flaw with to little heat dissipation.

Im pretty sure that they are zeners 12V and 24V in series on the bigger string and just one 24V on the little one.

So far i have not bought another new strip just replaced burnt zeners and the failed diodes take some time with hotair but it can be done.

Like the image i attached went from a dead strip to a working one.

[Acca]

Re: Samsung UN40F5500AF No back light

Well been some time since i was online here, and i have another suggestion that
i been modifying multiple sets to make them run cooler.

I been repairing some of these too about the same model but the sets i worked on
is called ue40fxxxx

R9119 R9219 if the value of these is 0.27 change it to
0.55-0.6 it makes them run cooler and they are likely never to fail again.

Then the voltage drops from around 180V over diode d9202c over the string with 52 leds down to 164 and you can then remove the glue on the pot and lower the voltage on d9102c to around 127V that use to be around 135V before modding it.

After this you are down at roughly 3.2V on the leds as samsung use to drive them at 3.46V is in my opinion to much.

I also apply a very small dab of heatsink compund to the backside of the strip where the led is mounted, i think it is a design flaw with to little heat dissipation.

Im pretty sure that they are zeners 12V and 24V in series on the bigger string and just one 24V on the little one.

So far i have not bought another new strip just replaced burnt zeners and the failed diodes take some time with hotair but it can be done.

Like the image i attached went from a dead strip to a working one.

Sorry for gravedigging a bit.
I've got one of this 40" samsung tv that I need to fix, is has 7 stripes with 13 LEDs on each, there are like 15 blown leds in total spread across 5 of the stripes
LEDs are not (much of) a problem to replace but what about the zeners? On some forum they are saying to just remove the blown ones and solder a wire instead, I guess it will still work but I'm curious, have someone finally found out what exactly are those and what can we replace them with?