Samsung S95B OLED Powerboard Failure Component Repair - Page 1
Forum section: electronics / repair

author: rikanana
author_rank: Contributor
timestamp: March 10, 2025, 06:00:06 am
content: One day the TV just didn't turn on. Strongly suspect an issue with the power board in the TV. Board is marked BN4401170A, L65QA9N_BDYTroubleshooting steps taken so far:Let it rest unplugged and plugged back in no life.Opened the TV up and thermal imaged the board with power connected nothing even getting warm let alone hot.Checked all fuses on the board no issues.Googled around a bit found info about PFC controller supply voltage with samsung TVs not starting at all. Was a very old model but ironically the IC is the same on the board.https://www.infineon.com/dgdl/Infineon-ICE3PCS03G-DS-v03_00-EN.pdf?fileId=db3a304329a0f6ee0129a683c9c92b50Found a lot of silicone smoo all over the board making reading the markings hard scraped off a bunch to find the markings.Did a smell test and visual inspection of the top side and all components nothing appears burnt, exploded, smoky, missing, etc...Poked the PFC Vcc pin and found it has 0V when the board PFC capacitors are <150VDC (120VAC incoming PFC controller is either not working or not enabled as its Vcc is 0V)All major rails 0V, 12V standby also 0V. Also started power board with all other boards disconnected no change.Checked all the bridge rectifiers they seem ok in diode checkHaving difficulty reversing the unmarked components and some of the SOT23 things (Marking RA3 sideways K) around the PFC controller as well as tracing out where the PFC Vcc supply is coming from as it snakes all over the place and if it has an enable hiding somewhere so isn't an issue. The board is a single layer board (topside is just through hole/jumpers/connectors). There is a small control PCB but I can't get good images of it without desoldering the thing as it is nestled between heatsinks.Not sure what is wrong with the board yet other than it doesn't seem to make any low voltage rails. Scanned of the top and bottom board to try and figure things out.Any helpful advise in poking the board more would be helpful.I also wonder how I could generate the power on signal but since I don't have a working TV I dunno what the logic level is yet.

author: ercan4434
author_rank: Contributor
timestamp: March 10, 2025, 06:15:24 pm
content: Hi,The part you marked as "ldo?" is a mosfet/transistor(if its the RA3 its a PNP BJT 50V 100mA) and it can be switching a high voltage because of the isolation slots in pcb. But I dont think it can cause the board to not generate voltages since the ICE3PCS03G needs external Vcc too. I think the problem is somewhere else.

author: rikanana
author_rank: Contributor
timestamp: March 11, 2025, 03:27:21 am
content: The part marked LDO? has no marking and isn't a SOT23. The smaller ICs are SOT23s and they are on HV resistor step downs.

author: rikanana
author_rank: Contributor
timestamp: March 11, 2025, 04:05:03 am
content: I realized I only took the thermal imaging from the topside not the bottom side after removing it from the TV and found the only warm spot in the entire TV is around JP810 or DS801 which feeds one of the ICs FA6B22N which has the enable for the PFC circuit. Probing it is quite hard with the conformal coat and it being fed by high voltages. The diode has an SF marking with a snowflake and is in a axial DO-41 style. The Vcc pin 10 has 0V and both power control ICs and the PFC circuit are fed by the same Vcc line looking around for the source on the board. I cant seem to find the datasheet for the 1st control IC also fuji electric marking 6C22616 and 6C13.

author: tom66
author_rank: Super Contributor
timestamp: March 11, 2025, 04:46:29 pm
content: PFC controller is probably off in standby state, either EN signal is low or more common Vcc is isolated from the controller by a FET/BJT somewhere. As there is only need for PFC when real power of TV is >50W, and PFC is typically inefficient at low power levels.Your issue is the missing standby voltage. Unplug the main board from the power supply and check voltages direct on power supply. If they are still bad, we can troubleshoot the power supply further. Without any output from the standby power supply, the main board can of course not turn on the power supply's main rails. If the rails return when the main board load is removed, I suspect a short on the main board instead.Since OLED load varies considerably with picture content, from nearly zero watts to 300+ watts full white, the power supply is split into two halves, with a regulated ~20-35V supply for the OLED panel (will go to T-Con) and a power converter which produces a 12V and probably 5V and/or 3.3V standby/run rail for the main board. The two supplies are necessary because it's difficult to get such differential regulation working reliably without a post-conversion step, and high power converters are often less efficient when running with low load, so it ends up being cheaper and more efficient to do it this way.I think the stby/main controller IC is this, it is an LLC controller IC:https://products.fujielectric.com/en/semiconductor/detail/FA6B22N/And it uses two FETs which are SMD on the back of the PSU to do the main switching. If you can check Vcc voltage pin 10 wrt to negative of main bulk capacitor, then you will understand the fault better.Assuming the standby supply is broken, there are a few likely causes;- Bad controller IC (If Vcc above shorted or low, this is very likely; if it is steady, and there is no switching, it is also likely)- Shorted output diode (If Vcc jumping)- Shorted output capacitor (ceramic type) (If Vcc jumping)- Bad LLC resonant capacitor - seen it before, but it's uncommon

author: rikanana
author_rank: Contributor
timestamp: March 12, 2025, 05:07:13 am
content: Thanks for the info,I tested the PSU outside the TV on the bench and all rails including the standby 12V rail read 0V. Also the Vcc pin on both LLC control ICs has 0V going into the pins. The bulk storage capacitors have DC voltage in them ~150VDC but the controllers don't seem to have their supply rail to even start in standby mode.

author: tom66
author_rank: Super Contributor
timestamp: March 12, 2025, 09:29:14 am
content: Is the Vcc pin on the ICs shorted (ICS801CS)? Repeat the same test on resistance with the PSU off and main caps discharged.Check QS801CS and QS802CS (SMD MOSFET) are not shorted too.It's also worth checking that the source of the 'lower' FET - Q802CS - is connected to the -ve bulk capacitor terminal, as there may be a current shunt resistor in that path burned out.But so far I suspect that IC is bad and replacing it would be a good start, it is not that uncommon for these ICs to fail due to the high voltages they deal with, the high voltage gate driver typically operates at 600V above the rest of the IC, so a mains power surge can kill it.

author: rikanana
author_rank: Contributor
timestamp: March 13, 2025, 04:01:49 am
content: I checked the two ICs that have the same footprint I think but slightly different part numbers the ICS801CS has a suspiciously low resistance of 8ohms between Vcc and GND while the other IC that is similar has 30kOhms. I will try and source the ICS801CS chip to replace and see how it goes. Thanks for the help!There warm spot also moved around which is suspcious and it is now QOS801 the tiny one near the IC that is the only thing that gets warm. I also realized that tracing around was getting confusing because as there is an unexpected short.

author: tom66
author_rank: Super Contributor
timestamp: March 13, 2025, 09:37:16 am
content: Yeah 8 ohms is definitely bad now you need to be sure only that IC is bad, I would remove QS802CS and check S/G resistance out of circuit to check it is not just the driver on the IC that has shorted, I am not sure what to make about QOS801 for now.

author: rikanana
author_rank: Contributor
timestamp: March 14, 2025, 04:25:23 am
content: Given that the replacement IC will take a few weeks to come I will check the QS802CS out of circuit on the weekend thanks for the advise I will keep posting updates as the repair attempt continues.Also QS802CS (The marking is confusing though as it shows up as a Magnachip 60R280Q (https://www.magnachip.com/wp-content/uploads/2020/10/MMF60R280QTH_Datasheet_v1.2_20210610.pdf) but this only comes in TO-220 but it cleaerly is a TO-263/D2PAK ex: 60R290Q,https://www.magnachip.com/wp-content/uploads/2020/10/MME60R290P_Final_Datasheet_v1.3_20210610.pdf)

author: tom66
author_rank: Super Contributor
timestamp: March 14, 2025, 09:37:19 am
content: Somewhat common for large manufacturers like Samsung to get a device they like manufactured in a custom package. In this case, if it were bad, you'd have to find an equivalent or better FET in a matching package as a direct substitute may not be available.Anyway, good luck with the repair.

author: tom66
author_rank: Super Contributor
timestamp: March 14, 2025, 12:51:50 pm
content: Also worth checking the small ceramic caps on the Vcc pin are not shorted, I had a couple of Panasonic plasma TVs that would fail to start due to bad ceramic capacitors on the Vcc pin of the controller ICs. CS815H and CS824H.

author: rikanana
author_rank: Contributor
timestamp: March 16, 2025, 02:14:41 am
content: Thanks I'll check the caps out first since that would be an easy fix if it was just them shorted. Edit: Poking the two caps for a bit they seem ok they hold a charge (since they are series connected poking individually worked fine 384nF for the shorted IC and 394nF for the good one with the same pinout) and there is no short on either cap to the middle junction between the two although the Vcc/Gnd is very low resistance still. I'm going to source a replacement mosfet before I remove it from the board probably something likehttps://www.onsemi.com/pdf/datasheet/ntd250n65s3h-d.pdfseems to be a good match. The footprint actual is also a DPAK3 (TO-252) when measuring with calipers so the package is likely custom as magnachip doesn't list that as even an option anywhere for any in that series. The specs for the mosfet seem comparable or better than the magnachip one.

author: tom66
author_rank: Super Contributor
timestamp: March 16, 2025, 10:26:40 am
content: Looks like a good match to me.

author: rikanana
author_rank: Contributor
timestamp: March 23, 2025, 02:23:08 am
content: I got replacement ICs from sketchy overseas vendors and got it from 3 different sellers as the ICs were cheap and fakes were likely. I think the middle set is probably the best bet on visual inspection the far left/right new ics look larger. One strip has inconsistent chips inside so that is probably not a good sign and the 2 pcs one seems larger and the pin1 locator is not in the same place as the original chip. The middle row is either a very good fake visually speaking or is the real thing.I'm going to try removing the mosfet first and check if it is still shorted and then replace both.

author: rikanana
author_rank: Contributor
timestamp: March 25, 2025, 03:41:00 am
content: Success at the board level at least. Both the mosfet and ic were bad when taken out of circuit they were both shorted either one failing likely killed the other somehow. The board at least out of the TV clicks unlike before and warms up multiple regulators at once. I have to recoat some of the board as I removed a bunch of the coatings to read part numbers. Removing the parts was very difficult because they use a lot of glue under ther components and the silicone coating also got under everything making removal very difficult I literally had to use a small amount of force to smack the components off.I used chipquick, a board heater to a very mild temp (80degC) to not upset the caps on the other side rated to 105degC, and a hot air gun to gently heat everything up replace the lead free with low melt and then use a lot of hot air with masked tape off areas to not cook everything and when it looked very melty I gave it a good tap with a spade metal wedge to break the glue and it came off with no pad damage luckily. I then cleaned off the low melt use flux with more flux then use lead free again with a hand iron to get the chips back on.

author: tom66
author_rank: Super Contributor
timestamp: March 25, 2025, 10:57:48 pm
content: Good stuff. You might want to power it up initially without any connection to the OLED power output, just to verify the board voltages are OK so you don't damage the OLED panel if something is wrong. Unlikely to be an issue - but shouldn't hurt to be cautious.

author: rikanana
author_rank: Contributor
timestamp: March 30, 2025, 04:43:55 am
content: I checked the 12V standby rail and it was good the board also powered up all the other sections with no abnormal temperatures seen in a thermal image. So after that I cleaned up the area where the TV went previously and moved it all back and turned it on. It worked perfectly after that which was nice as Samsung was quoting 250USD just to come look at it and online the board can run in the hundreds of dollars to get even used which is why I wanted to try doing a component level repair on it.From what I gather lots of these samsung TVs are having dead power supply problems after only a few years while I've had/seen OLED TVs from LG and other brands last many many years with no failures. If it dies again I might just jump all the leads going to the boards and plug it into a bench PSU...Thanks for the help!Also it was also super handy using a CCD flatbed scanner as it can scan PCBs pretty well which is how all the images of the board were taken.

author: tom66
author_rank: Super Contributor
timestamp: March 30, 2025, 09:17:35 am
content: So glad you fixed it, good work. And yeah your board pictures were great, if only other people's were all like that!