Samsung led strips not working

[budm]

Re: Samsung led strips not working

Just got home. How do I tell what range of diode to buy? I don’t see any markings on the bad one.

Look again at the marking, is it SF28G?
Your LED power supply board uses the same topoly as used in this thread (BN44-00772a):
https://www.badcaps.net/forum/showth...28G#post854858

[vinceroger69]

Re: Samsung led strips not working

bubm i wondering if its the correct part hes testing as says dosnt see any markings? maybe hes got the silk screen confused and has removed the ferite bead? bb9004 below the diode

[larryf]

Re: Samsung led strips not working

Ok, so I took the diode out of the board and it says SF28G on it. Checked wit both of my meters and in resistance mode I get 077 both ways. In ohms mode with black lead on the end with the stripe I get76.9. When I switch the red lead to the striped end ,I get 77.3. Does this make any sense to you? You were right, I was testing the wrong item. I am old and my mind is not what it once was.

[vinceroger69]

Re: Samsung led strips not working

in diode mode what does it read it should read in one direction only

[larryf]

Re: Samsung led strips not working

I will try to get a replacement diode on Thursday when I take my wife for her Chemo treatment. The electronics store is a couple of blocks from her doctor and will only have to make one trip that way.
Will put it in the board and retest and post the numbers .
Thanks again

[larryf]

Re: Samsung led strips not working

I need to ask another question about the bad diode. The writing on it is SF28G, but also STYU JG01. Do I look for one with all the writing, or just the SF28g? I found some on the internet with SF28G, but the other letters were different.
Or is there a comparable one that would work? Sorry for my lack of understanding.

[budm]

Re: Samsung led strips not working

SF28G that is all you need to go by.

[vinceroger69]

Re: Samsung led strips not working

maybe also advisable to get a couple just incase you have more than just a bad diode issue and it shorts out again until you replace that part we dont know if you have just the one issue or not.

[larryf]

Re: Samsung led strips not working

So I got the SF28G diode and installed it in the board. It read 494-1 out of the board and 489-1 in the board. No leds came on so I retested and got these readings D- 320; S+ 384, S-384, and. D+ 429. Basically the same as before. I left the tv on for 10 minutes and the diode did not blow. What do you think?

[larryf]

Re: Samsung led strips not working

Does any one know what the voltage readings should be going to the led strips on this tv?

[vinceroger69]

Re: Samsung led strips not working

326v 410 mah (printed on the board).
so these are your latest readings D- 320; S+ 384, S-384, and. D+ 429. ?

[larryf]

Re: Samsung led strips not working

Yes, those are the numbers after replacing diode.

[vinceroger69]

Re: Samsung led strips not working

maybe time to test the leds too rule them out have you got a led tester? have you taken a lcd panel apart before? remember there is always a risk of cracking the lcd panel doing this though.

[larryf]

Re: Samsung led strips not working

No, I don’t have a tester and since this may be the only tv I try to repair, investing in equipment dose not make a lot of sense. Warranty has replaced tv, so if I break the panel, I am no worse off. Can I string batteries together to match volts of each strip and see if they light up??

[vinceroger69]

Re: Samsung led strips not working

lets wait and see if budm will advise any more tests on the psu first and yes you can use two 1.5 v batteries too test each led if they are the 3v type just test across each led in turn and see if any dont light up,whilst you are waiting too see what budm suggests maybe have a look on youtube some very good guides on the lcd panel and also testing the leds ( having a led tester just means you can power each strip without having too take the panel apart)

[larryf]

Re: Samsung led strips not working

Ok. Thanks.

[budm]

Re: Samsung led strips not working

At this point, based on the D+ reading, the LED driver output is not seeing the load or no load current return path so the output went up to 400V.
You can test each LED strip if you know how many LED's are on the strip.

[larryf]

Re: Samsung led strips not working

I think I will take the panel out and see what I can find out. I thank you guys for all your help.

[larryf]

Re: Samsung led strips not working

I am ready to remove the panel. I disconnected the ribbons from the t-con board and unhooked the buffer boards and taped them to the panel. When I go to lift the panel, it seems to be stuck to the frame at the bottom. Is there some glue or something there ,or something else I need to release? They do not show this on the video on Shopjimmy.

[larryf]

Re: Samsung led strips not working

I got the tv torn apart down to the led strips. I plugged it in and this is what I found. I had 43 of 84 leds glowing faintly. There are 14 leds per row and 6 rows. Here are volts and leds glowing per strip from top to bottom.
Volts Leds glowing
11.9. 5
14.3. 6
16.4. 7
14.0. 6
16.9. 9
16.9. 10

Do you think replacing the strips would fix it or could there still be something else wrong with it. It is not an expensive tv so it does not make much sense to throw a lot of money at it unless it might last a while.

Either way, I have enjoyed working on it and maybe learning a little bit in the process. I guess we never get too old to learn and electronics are fascinating. Thanks for your imput.