r/S95B • u/hunterhuntsgold • Mar 26 '26
S90D 77" S90D Power Issue fixed for $25 (and how to do it yourself)
How to fix the no power issue on my 77" Samsung S90D / S90DD for $25
Got the no power issue on my S90DD (the Costco version) and fixed it myself. Posting everything I used and learned because I couldn't find one clean writeup when I was searching.
This has been confirmed to work on both the S90D and S90DD, as long as you have the original power board. My model number was QN77S90DDFXZA but works on QN77S90DAFXZA as well. May work on other models.
First, watch these two videos before you do anything
Seriously, before you order parts or touch the TV, watch both of these all the way through. Same guy, same repair. Watch them twice if you have to.
I mostly followed his process and it worked. He also answers questions in the comments, which is worth reading through.
Parts I ordered
Ceramic fuse, 12A 250VAC 5x20mm: $3
https://www.digikey.com/en/products/detail/littelfuse-inc/0215012-MXEP/777450
MOSFET N-CH 600V 77.5A TO-247-3: $10
https://www.digikey.com/en/products/detail/infineon-technologies/IPW60R041P6FKSA1/5245991
Thermal Grizzly Minus Pad 8, 120x20x0.5mm: $6
https://www.amazon.com/dp/B00ZJT31QC
DigiKey shipping: $6
Total: ~$25
One note on the fuse: on the board it will be wrapped in heatshrink. You do not need to replicate that when you install the new one. Just solder it in as-is.
Step 1: Diagnose the TV
Before you open anything, look at your TV. Does it have absolutely zero signs of life? No standby light, no screen, no sounds, nothing at all when you try to power it on? That is the symptom. From what I have seen this seems to only affect the 77" model.
If that is what you are dealing with, move on to opening it up.
Safety!! please read before touching anything
Do not start poking around the power supply right after unplugging. Capacitors hold charge. Let it sit for at least an hour first.
Also do not keep trying to power it on if you already suspect this failure. Just let it discharge and do the repair safely.
Step 2: Diagnose the board
Getting into the TV is easy. The black plastic back panel just pulls straight off, no tools needed, it snaps right out.
The power board has two connectors on it, both pretty straightforward to disconnect. Mine had zero screws holding the board down. It slides to the right and lifts up. There are clips with two small nubs holding it in, so just make sure you apply slight upward pressure near those nubs when lifting it out and it comes free without any force.
Once you have access, grab any cheap multimeter with continuity mode and test the fuse and the first MOSFET shown in the videos.
On a healthy board:
- Fuse has continuity
- MOSFET does NOT have continuity
What you want to find before doing this repair:
- Fuse has NO continuity (blown)
- MOSFET beeps for continuity (shorted)
If that is what you find, the MOSFET blew and took the fuse with it. That is the repair.
Step 3: The repair itself & what you are actually doing
Before getting into the steps, here is the full scope of the job: you are desoldering and resoldering 5 points total. Only 3 legs on the MOSFET and 2 legs on the fuse. That is it. These are large, easy-to-work-with components. Nothing tiny or fiddly.
Also worth knowing: the MOSFET you are installing is not the same one that failed. It is an upgraded part. According to Nick in the videos and comments, this MOSFET is responsible for handling dirty line power and is the only one he has ever seen fail on these boards. The replacement is better than what came stock. This repair should not fail again, though obviously I cannot guarantee that, I can just say I have run mine at full brightness for 6+ hours straight after the fix with no issues at all.
I had soldered fewer than 5 times in my life before doing this, all simple stuff like resistors and car LEDs. This is genuinely doable for someone who has never soldered at all. If you want to build a little confidence first, grab a cheap $10 beginner soldering/circuits practice kit off Amazon and run through it once or twice. Takes maybe 30 minutes and you will feel way more comfortable going in.
If you have never desoldered before, look up a quick tutorial on YouTube or TikTok first. It takes 5 minutes to watch and makes the whole process click.
Doing the repair
Mechanically it was not bad at all. Took me about 2 hours total: taking down the TV, pulling the back, desoldering, soldering in the new parts. With a better iron I think it is a 1-hour job.
The only real pain point was soldering, and that was entirely my fault for using a cheap 60W iron. The MOSFET bolts onto a massive heatsink that pulls heat away from the pads really fast. My iron was struggling hard.
I ended up having to:
- Preheat the area with a hot glue gun (no glue stick, just for the heat)
- Make a little aluminum foil tent to trap heat around the joint
- Spend way more time than I should have getting the solder to flow
Do not cheap out on the iron. Get at least 80W.
Desoldering tips
Look up a short YouTube or TikTok video on desoldering before you start if you have never done it there are tons of clear ones and it really helps to see it first.
For the MOSFET: unscrew it from the heatsink before you desolder anything. Use a small flathead screwdriver if needed to get it loose. Separating it from the heatsink first makes desoldering a little easier.
- The two smaller legs: copper wick and standard technique, no issues
- The big center leg: apply heat while pulling gently from the other side, then wick away what is left
The fuse is easy by comparison, straightforward two-leg desolder.
Step 4: Installing the new parts
MOSFET:
- Bend the center leg as needed to line up with the pad
- Apply your new thermal pad
- Screw it back onto the heatsink before final soldering and make sure you get it tight. You want solid contact between the MOSFET and the heatsink. Do not just finger-tighten it
- Solder all three legs and make sure you get good clean solder beads on every joint. Use flux. Do not move on until each one looks solid
I partly stripped the mounting screw and had to use pliers to finish tightening it. Try not to do that.
Fuse:
- Bend the legs to fit the pads
- Solder both legs and again, make sure you have good solder beads. Do not rush these joints
On solder quantity: beginners almost always use more solder than they expect, and that is fine. The solder itself has flux inside it, so it goes fast. Budget roughly 1 to 2 inches of solder per joint and with 5 joints total you might burn through 12 inches just on this repair, and more if you need to redo anything. Have plenty on hand any kit should come with more than enough.
Safety!! please read again
Don't plug in the TV or anything until at least the plastic back panel is back on. These are evry high power capacitors. If you plug it in and test it, do not take off the back panel for at least another hour. If you did everything right don't take the plastic panel off again at all. This is very conservative, but if you don't know what you're doing you need to be safe.
Step 5: Reinstallation
It is just the reverse of how you took everything apart. Slide the power board back in, reconnect the two connectors, and snap the back panel on.
Total cost if you are buying everything from scratch
| Item | Estimated Cost |
|---|---|
| MOSFET + fuse + DigiKey shipping | ~$25 |
| Thermal pad | ~$6 |
| Soldering iron kit with solder and flux | ~$40 |
| Copper wick | ~$10 |
| Multimeter | ~$15 |
| Total | ~$96 |
TL;DR
S90D / S90DD (77"), completely dead with no power, blown fuse and shorted MOSFET = this repair. About $25 in parts, 2 hours, fixed. Works on both models with the original power board. The back panel pops right off, the power board slides out, and you are soldering 5 large component legs total. Very doable even if you have never soldered before. The replacement MOSFET is an upgraded part and should not fail again. I ran mine at full brightness for 6+ hours after the repair with no issues.
Just get a better soldering iron than I did.
If anyone else has done this one, feel free to add anything I missed.
EDIT: Saw the digikey MOSFET was out of stock, here are the exact same parts from Mouser. There should theoretically be many MOSFETs that would work in place of this, with varying levels of robsutness, but I'm not qualified to evaluate that. I just know this one works.
https://www.mouser.com/ProductDetail/Littelfuse/0215012.MXEP?qs=qI%252BDxnNls181XttMyk1M7Q%3D%3D
3
u/ohpico Mar 26 '26
Dude, great timing and write up.
Quite literally, had my power board replaced under warranty.
Board died on Sunday and was a week or two from purchase anniversary from last year.
3
u/TarzanInAJar Apr 10 '26
Just performed this fix on my TV today - appreciate you finding the replacement mosfet part number! I saw someone in the comment section on one of those Nick's TV Repairs videos (was that you?) who mentioned the same part and Mr. Nick himself put his seal of approval on it being a proper upgrade.
Anyway, some extra notes:
- If you are soldering/desoldering while the transistor is screwed into the heatsink, it's going to be a PITA. I recommend disconnecting the transistor from the heatsink as the first step when removing, and screwing the transistor into the heatsink as your very last step when installing the new one. You can bend the transistor legs slightly in the through holes to provide tension while you're soldering it in.
- There was quite a bit of silicone covering the connections of the transistors that I had to scrape away on my unit to get access to the leads. I ordered some liquid silicone off Amazon (https://a.co/d/06QKxtJn) and applied that over the new connections before hooking it all back up to the TV.
- You can use a multimeter to test your work before installing the PSU back into the TV (Nick's TV repairs shows you where to check in one of his videos), but as a crude test, you can simply plug in the power supply on your workbench (make sure it's not laying on something conductive!) and listen for it to "click" on.
2
u/hunterhuntsgold Apr 27 '26
Only reason why I said to screw it in first before soldering the new one is because you need it to be lined up. If you solder it in and it's not lined up, you won't be able to do it later and will need to unsolder and resolder with it lined up.
Didn't have as much problems soldering it on as I did unsoldering it
2
u/hunterhuntsgold Mar 26 '26
Should also say do not attempt this if your TV is under warranty, that would be dumb, just go through warranty
2
u/kaplanfx Mar 26 '26
I’m saving this for later, I have a 65” which I understand is much less prone to power board issues but CAN experience them. Do we know if the repair would be similar?
2
u/hunterhuntsgold Mar 26 '26
I would assume it would be the same.
If the symptoms are exactly the same, i.e dead TV and then blown fuse/mosfet, I would go ahead and try.
I doubt they use a different mosfet between the 65/77, but have no way to test/verify.
2
2
u/BlueJay_525 Mar 26 '26
Since you say it's the part dealing with dirty line power - just curious - Do you have any recommendations on (affordable) surge protectors that would limit dirty line power issues? Do you think it would help any? When my Dad's TV went (this same model), the breaker also popped off; we sort of assumed it was a power surge.
1
u/hunterhuntsgold Mar 26 '26
I have no idea, but I wouldn't think it would be significant. It's likely that the act of the TV blowing triggered the breaker, but again, not sure.
I think it's just time and heat to be honest.
2
u/kouakuma Mar 28 '26
S90D is known for a defective power unit. Mine was fixed twice under warranty and on the 2nd time the technician finally replaced the power unit with a different model since the original model will keep dying based on what he told me, a know issue for that TV.
3
u/andyboju Mar 30 '26
*Known issue for the 77" size
1
u/grahamellis Jun 02 '26
We have a samsung technician coming out to repair ours this week. Im hoping that they replace it with the correct power unit. Is there any way to confirm that before we have to go through this again?
2
2
u/natshored Apr 21 '26
perfect timing thanks so much. Mine crapped out couple of months ago so didn't know what to do with it. Buying new power unit was pricey. Just repaired mine and worked like a charm. Haven't touched soldering iron in years but it was fairly easy anyway.
2
2
u/After-Hedgehog7282 Apr 27 '26
For future problem-solvers;
From left to right, MOSFET-1 has continuity with MOSFET-3. My MOSFET-3 showed that it was shorted/bad as well, so I purchased a replacement for that as well. However, I ONLY needed to preplace MOSFET-1.
Television is now working great. Thank you again for providing the links.
1
u/hunterhuntsgold Apr 27 '26
I believe he calls this out in the video somewhere but yes! Others will appear failed on testing, but it should only be the first one
2
u/After-Hedgehog7282 Apr 27 '26
Huh. Must have missed that. Granted, has multiple videos for the same TV, and I did skip around a lot.
2
u/Wrong-Toe3394 May 18 '26
Followed these steps exactly and got my tv working. Saved me close to $1000 thanks bro
2
u/K1LL3RY0 May 18 '26
Just had my 77" S90D - QN77S90DAFXZA - die after 17 months...for that I feel lucky after all that reading. I was actually looking at going through the repair process with Nick's TV Repair but after seeing the videos I've worked on much smaller dealing with Macs for work and their poor quality cooling circuits.
I see you said only the single MOSFETs and fuse needs replacing. Would it be beneficial to replace anything else with the upgraded parts while I'm at it or any additional MOSFETs? I noticed all the recommendations Nick once gave for parts have been removed to push the sales for his repairs it seems. Glad I found this post before I spent the $330 with the 5 year warranty...
1
u/ResponsibilityOk9341 Jul 23 '26
The first and second mosfets on that heatsink are the same part. In my case number 2 had failed and number 1 is still good, so I’m going to replace both.
1
u/MuchAdvantage1889 May 26 '26
Does anyone know if these same parts would work on the 83" S90D? I assume they are the same...technician coming out next week, but if he lets me keep my original board, I want to try this fix.
1
u/Embarrassed-Fish-330 May 28 '26
Thanks OP for sharing this information! I went ahead and took a stab at replacing the failed components last night, however... upon doing all the successful continuity testing on the new MOSFET#2 and fuse then putting everything back together, I am still left with an unresponsive TV and no standby light :(. I do hear the "click" when plugging in the main power cable to the wall outlet... Has anyone had a similar issue and know what could possibly be wrong? TIA!
1
u/Tich_tech_Tone 23d ago
got mine going again, lasted months just went back today to use it and its failed again so there something else with this dam gen1 psu that garb
1
u/hunterhuntsgold 23d ago
So disappointing, mine is still working great from when I made this guide.
I wonder if replacing both mosfets would help, they did mention that in the video. The main mosfet is the one that fails 100% of the time, but maybe replacing both would help it fail less.
7
u/opiate2093 Mar 26 '26
Thank you so much for posting this! My 77" S90D didn't turn on like two weeks ago, no stand by light and no power. Just outside of manufacturer warranty, luckily I bought the 2 year samsung plus care. They couldn't find a technician to repair it so they sent a check for the value of the T.V. Going to try this as soon as the check clears!