Samsung recent models can do as yours for only motivation bad backlight, the square is now possible damage by mains spike, damaged both main board and B.L. leds, your work is done well until now, do not give up, maybe take some break days an then under to replace strips, not sure 100% is faulty strips, but the non working BL PS board can be due to overloaded by shorted bars, freeing the panel's load the leds turns back half on, the PS is for me for supply the entire panel, back and front..
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Thank you very much Davi,
needed a little break but have ordered the Backlight strips and now waiting for them to arrive. Didn't know that a faulty Backlight can cause so many more defects. I couldn't explain to myself why so many different things were damaged
Thanks for your explanation... will disassemble the TV tomorrow and hope not to damage the panel. Honestly... This TV is so overly complicated and the whole electronic is designed not to be repaired by someone. But this is just a beginners opinion.Comment
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No the backlight can't damage other boards, it's the mains spike that can damage several parts..Comment
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This is not true, bad backlights CAN damage a powerboard.Originally posted by Davi.p View PostComment
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My Backlight strips have finally arrived, so I replaced the faulty strips with the new ones. One LED was burned and this was on the left side. Was a little bit scared but I did everything very slowly and carefully.
The swap of the Backlight strips was successful but I have no luck with this TV 😪 The already mentioned Buzzing noise is still there and there are more faulty components. The voltage on the diodes is OK but not one FET. This FET is exectly for the Backlight strip that had the shorted led on it.
So.... the search goes on. Have to check every single component in this circuit and find the defective one. This TV gives me a big headache.Comment
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Can you point well which diodes / fet are talking of? Have you checked D9101C and D9201C? and the other axial diodes on secondary?Comment
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My apologies for the late respond but I had some long workdays and no time to go on with the repair.
Yes, this are the diodes I mean. They have around 183V and this looks good in my opinion. What I found out is that the Mosfet driver - MC MAP3612B - was shorted. I have replaced it with the only one i had but I've had already solder and desolder this thing for a couple of times... for learning purposes 😊
I don't know if this driver is really full functional or not... I hope and it looks so.
the loud buzzing noise is no more but still no backlight. I hear the typical Samsung startup sound and so I know that the TV is on. The Backlights are off, cause of the voltage on the Mosfets.
The upper one Q9201C has only 96V but stable and the lower one Q9101C a dropping voltage around 5V. So.... no success yet.Comment
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You have to check in diode mode both mosfets all three pins, and also the shunt big resistor on both source pins, if you have short on drain-gate also the pwm ic is bad, but since of those 183v the ic half working it rather can be..Comment
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I've checked them a few times and they are good. I truly believe that my ic is not working properly. Got the ic from a junk board I used for soldering practice.
Unfortunately I soldered and desoldered this little thing too often... and unfortunately it's the only one I had of this type...
I guess I have to order another one from Mauser or RS.. or Aliexpress. A bit frustrating when you always don't have something in stock.Comment
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It's an uncommon scheme for backlight this board, i think that the destructive peak runned along to a led bar, but also on some other parts, the IC gets the current state from the big resistor on the source pin, trough a resistor, it's in a safe position i guess, but the big resistor must be tested!Comment
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Thanks for the information. Since I don't understand everything yet, I'm very grateful for any explanation.
I've ordered the IC on Ebay cause I've found no other source for it. Not even AliExpress wanted to deliver this IC it to Germany.
The Resistors are ok but I have exactly the same on a Samsung junk board so I can replace them if needed.Comment
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Have you replaced all led strips?.Very often strips appears good but they aren't... if you haven 't, the most supicious are them cause power board appears ok..Comment
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Yes, this TV has Edge LED Strips so there were only two to replace. The left side had one LED with black marks on it. It was definitely burned ...
I believe that it's like on the primary side. Everything was ok and I had no shorts there except the Fa6B19 IC. On the secondary side I found a short on the MAP3612B IC
and replaced it with the only one I had... but i tortured this IC so many times with my hot air station for learning purposes that this thing isn't working as it should anymore.
Haven't expected that I would need exactly this one so badly now.Comment
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what type of test showed you short circuit on those IC? Did you checked in ohm between the 2 poles of the 2 lamp outputs? And so verify the two square caps, not to be shorted maybe..Last edited by Davi.p; 05-20-2025, 11:46 AM.Comment
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before you went to damage the IC i wrote to you at post #7 the edge BL and how zener diode build in !!Originally posted by ChristianBr01 View PostComment
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I know, I know Diah... You've been right and I did it the wrong way. Lesson learned, I hope 😉
I tested the IC in Beep mode and than measured the resistance to ground. I have a 0,1 Ohm resistance to ground on pin 14 and this is not wright!
I've desoldered the IC and measured the resistance between pin 5(GND) and pin 14(ADIM) off the pcb and the result is still the same 0.1 Ohm. On my replacement IC the resistance between GND and ADIM is in high KOhm range.
Will check the rest later but I have a another problem since Tuesday with my PC Monitor. Will post it "Troubleshooting Computer Displays".Comment
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Short on ADIM INPUT sounds very not good, as it is not connected to the leds loops in any way, this sounds strange to me, the ADIM is connected to the main board and especially with CPU, so not good at all..Comment
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So whats wrong, replace the ic with a good one.Originally posted by ChristianBr01 View PostComment
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A new IC is already ordered but has not arrived yet. Will replace the IC as soon as I get them.
Davi.. when this shorted ADIM PIN goes to the MB, could this be the reason why I burned the IC on the MB like I mentioned in post #13?
I replaced the TI IC and the MB is working cause the typical Samsung startup sound is there...Comment
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No it has nothing to do with it..Comment
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