Samsung LN40A550P3F Power Supply Board BN44-00198A - Page 1
Forum section: electronics / repair

author: edy
author_rank: Super Contributor
timestamp: February 03, 2021, 03:11:41 am
content: While walking the dog, I spotted a 40" Samsung dumped for garbage on the curb in the snow! Next morning I swung around in the car and was able to take it. It's circa January 2009 and having repaired a few of these I figured there was a good chance it was just some bad caps on the power supply board.Full model is LN40A550P3FXZC version CK10 and the power supply board is BN44-00197A made by Hansol. There is one obvious bulging/leaky cap at CM810, and a whole bunch around it which I suspect are troublesome as well. I've attached some photos.I couldn't help but turn it on, noticed the usual turning on and off cycling, every few seconds, just enough to hear the start of the familiar Samsung "chime" sound that plays when their TV's turn on. Then it would turn off and after 5-8 seconds try again to boot up. Initially the backlight would even flick on for a second and then it just doesn't have the momentum to do even that.... Just the first little bit of the chime.I want to replace the caps and noticed lots of kits available. I was hoping someone would know what typically comprises these kits so I can see if I can gather the parts myself and swap them out without needing to order and wait for a kit. Also I previously have replaced caps with their higher voltage counterparts. For example, a previous Samsung of the same era seemed to be using a 10 V cap on a 12 V rail and I switched them all to 25 V but keeping same capacitance value. Any suggestions? You'll notice in the picture the CM810 looks leaky and it's also 10V.Any schematics or capacitor kit location/values would be helpful. Thanks again! Looking forward to saving this TV from landfill, it's a shame.[EDIT:]I managed to find a schematic for the 197A board on Elektrotanya... I'll see if I can gather any more clues. I doubt a service manual exists but I'll keep looking. A screenshot shows what seems to be the affected section.I just found this... May be handy:http://vi.raptor.ebaydesc.com/ws/eBay%20http://vi.raptor.ebaydesc.com/ws/eBayISAPI.dll?ViewItemDescV4&item=181986683870

author: edy
author_rank: Super Contributor
timestamp: February 03, 2021, 06:42:10 pm
content: Hi, just a follow-up, I found a YouTube video that pretty much shows a similar issue and the person repaired the two nearby caps (I'll link it below). I have a question regarding Voltage rating for the caps because I cannot get the exact values. Here are the 6 sites and original specs, plus the caps that I can source to replace them (although some have higher V rating):1. CM808 - 220UF 25V:I can only find these 2 options at my local parts shop. The other options are rated for 10V, then it jumps up to 35V (no 25V options):ESM227M035S1A5H150 CAP LYT RDL 220UF 35V 10X12MM Stock No.: CER-273AA-2 (1 pc/pkg)CAP LYT RDL 220UF 35V 8X11MM 105C Stock No.: CER-273C-2 (2 pc/pkg)2. CM810 - 470UF 25V:I can find these. One is rated 25V, but if I want ESM the next jump up is 63V. Note that the original on the board is 10V right now.CAP LYT RDL 470UF 25V 8X12MM 105C Stock No.: CER-304A-2 (2 pc/pkg)ESM477M063S1A5L250 CAP LYT RDL 470UF 63V 13X21MM 105C Stock No.: CER-307A3. CM804 - 1000UF 25V4. CM806 - 1000UF 25V5. CM809 - 1000UF 10V6. CM812 - 1000UF 10VOk, so for the following 4 more sites, I need 1000UF either 10V or 25V. However, I don't have any options for 10V at my local shop. The only options I have are 25V and they are as follows:ESM108M025D1S5L200 CAP LYT RDL 1000UF 25V 10X20MM 105C Stock No.: CER-317M-2 (2 pc/pkg)CAP LYT RDL 1000UF 25V 10X20MM 105C Stock No.: CER-317H-2 (2 pc/pkg)CAP LYT RDL 1000UF 25V 10X17MM 105C Stock No.: CER-317K-2 (2 pc/pkg)Any thoughts? Should I get ESM if they are available, or regular? Can I bump up the voltages as you see in this case? I will have to measure and see if there is space on the board but I remember on my last repair it was a tight grouping especially when needing to increase to higher V-rated caps they get larger and the board is crowded.Here's the video, in it he shows 2 bad 1000UF 25V caps.... he just replaced those 2 and TV working again. I think only CM810 on my board is bad but I wonder if I should be replacing all 6 as a matter of fact:

author: edy
author_rank: Super Contributor
timestamp: February 09, 2021, 03:00:48 pm
content: I will need further help if anyone has any suggestions. I've gone ahead and replaced most of the caps and checked all of the caps indicated on most repair kits. That is, all of these positions:1. CM808 - 220UF 25V2. CM810 - 470UF 25V3. CM813 - 47UF 50V4. CM804 - 1000UF 25V5. CM806 - 1000UF 25V6. CM809 - 1000UF 10V7. CM812 - 1000UF 10VHowever, I still get the same symptoms. TV tries to power up, red light goes on, I hear just the first part of the Samsung "startup" sound effect (first half second) and then it cuts off and TV goes off again. Then about 2 seconds later it tries to start up again... cycles through the exact same thing.Where do I go from here? Do I just keep checking more caps on the power board? I changed the one obvious defective one CM810... it was the only burned cap which I checked and confirmed it was toast. However, all the other caps I swapped out checked out fine, but I replaced them anyways while I was already in there just in case.

author: drussell
author_rank: Super Contributor
timestamp: February 09, 2021, 04:08:40 pm
content: Quote from: edy on February 03, 2021, 03:11:41 amIf it was quitting right when the backlight was coming on, perhaps it is something up with the backlight circuitry, a short or something that sends it into protection?Is there a way you can somehow totally disconnect and disable the backlight PSU circuit and see if it fully boots up? Pull a transistor or something? I would need better photos of the front and back of the board or more schematics to point you to precisely where and how you might be able to do that.

author: drussell
author_rank: Super Contributor
timestamp: February 09, 2021, 04:11:30 pm
content: Quote from: edy on February 09, 2021, 03:00:48 pmTry to figure out exactly what it is doing when it quits. Check each voltage, etc. Something will be trying to start, something changes which makes it go into protection. You need to identify what circuit is trying to come up when it dies so that you can trace back why that might be occurring. Often this can be inferred by figuring out what rail is just coming up or what state changes in the overall startup flow when it quits.

author: wraper
author_rank: Unknown
timestamp: February 09, 2021, 04:14:42 pm
content: Quote from: edy on February 03, 2021, 06:42:10 pmAnything among those is not suitable. You need LOW ESR capacitors. If you use general propose capacitors, TV will fail again within a few months.

author: drussell
author_rank: Super Contributor
timestamp: February 09, 2021, 04:38:22 pm
content: Quote from: wraper on February 09, 2021, 04:14:42 pm+1, yes I meant to mention that.It is quite possible thatedyhas replaced some fully functional capacitors with inferior ones which are not suited to the usage in the actual circuit.Most of the lower voltage capacitors on the secondary side of the PSU must be low ESR types suitable for handling the high frequency, high current pulses of a switching PSU in their intended filter duties. Standard general purpose capacitors are unsuitable and won't work.

author: edy
author_rank: Super Contributor
timestamp: February 09, 2021, 04:40:46 pm
content: Thanks for the help. I've attached the schematic for the board. You can see all of the caps that I've replaced in the schematic, listed in the previous post... That covers 90% of repair kits out there. There are a couple kits that also include CM801 and CM803, both 10 uF 50V caps, but they look fine. Those are all the caps in most "repair kits". Figuring that CM810 was bad, could it indicate a cascading fault that can trace itself from that bad cap that took out other things down the line (or perhaps point upstream to a flaw that caused the cap to over-voltage)?[UPDATE: Perhaps I should switch back all of the good original caps and see what happens. Note that I used a multi-tester and all new caps came up measuring ESR < 1 ohm]?

author: wraper
author_rank: Unknown
timestamp: February 09, 2021, 05:14:49 pm
content: Quote from: edy on February 09, 2021, 04:40:46 pmGeneral purpose capacitors should work, but not for long.

author: drussell
author_rank: Super Contributor
timestamp: February 09, 2021, 05:24:44 pm
content: Quote from: wraper on February 09, 2021, 05:14:49 pmAgreed.There is seemingly some other issue with this set beyond simply some typical failing PSU capacitors.This unit is LED backlit? Some good photos of the whole unit back and each board would be helpful.

author: edy
author_rank: Super Contributor
timestamp: February 09, 2021, 09:24:01 pm
content: Thanks, I will take some more photos and post them in a few hours (when off work). Meanwhile I had a brief look at the start-up sequence again and noticed something (perhaps important). As soon as the TV is plugged in (I'm not pressing any buttons or remote)... the red light turns on, then off, then on again, then off (about 1 second for each "on" and "off" period) and then on the 3rd time it turns on, that's when the Samsung "music" briefly plays (about 1/2 second) and then cuts out together with the light. Then after about 3 seconds the entire cycle repeats:PLUG IN at time 0.0s: (no buttons pressed, no remote used)0.0s - red light immediately turns on1.0s - red light turns off2.0s - red light on again3.0s - red light off again4.0s - red light on / Samsung "music" starts4.5s - all off (red light off, sound cuts out)...7.0 s - cycle repeats from 0.0s like beforeI'm just wondering if this is some kind of "code" that the TV is trying to tell me something. Why the red light blinks twice before any sort of sound, and then why it tries the last blink and cuts out... may indicate where the error is, what it is trying to power up at the time it cuts out. I looked online but couldn't see anything specific about 3 blinks... may just be the startup sequence of this particular model, and at what point certain circuits charge up to start their job and when the fault protection mode kicks in.Before I post photos, just note it is an LCD TV circa 2009. There are only 4 boards... 1) power supply, 2) main processing board, 3) backlight inverter board (running vertically along side of TV) and 4) T-Con board located near top of TV (connected with large flatflex to the main processor board). I thought that disconnecting the backlight inverter board (in case there was a fault there) would help, so I disconnected it and tried but the TV still didn't power up. Same sequence. I can try to probe the power board with nothing connected and see what voltages I get out of the connectors as they are all marked with nominal values that they should be at.

author: edy
author_rank: Super Contributor
timestamp: February 10, 2021, 05:52:10 pm
content: I've attached photos... Basic 4 board layout. Backlight inverter cover removed. T-con board is stuck to the metal cover plate with some sponge tape, I didn't want to rip it, but I highly doubt it is the problem. I tested voltages on large 24 pin output ribbon connector and getting 4.9 on the 5.3V and about 12.5 on the 13V. It then drops to 0 when the "reset" occurs and sound cuts off (after the 3 red LED flashes). Then goes back to those voltages again until the next time it starts making the Samsung sound then abruptly cuts off, voltage 0 and then back again. Maybe protection circuit kicks in and turns it all off. Are those voltages too low or within spec? I checked ground to one side of CM801 and getting 18V. That's as much poking as I wanted to safely do on that side of the board. I'll have to flip it over to get test points on the green side if needed.

author: tunk
author_rank: Super Contributor
timestamp: February 10, 2021, 06:12:41 pm
content: Don't really know much about SMPSs, but over time watchingsome youtube videos, I'm left with the impression that someSMPSs have capacitor(s) in the circuit providing power tothe switching controller. Maybe you could check the rest ofthe capacitors?

author: drussell
author_rank: Super Contributor
timestamp: February 10, 2021, 07:37:01 pm
content: Have you checked out C102 on the main board?That is apparently asupercommon fault on these A500 and A550 series of all screen sizes.Try tacking a 100µF low ESR of at least 10 volts rating across there and see if it boots up:

author: drussell
author_rank: Super Contributor
timestamp: February 10, 2021, 07:44:22 pm
content: Oh, it is on the back of the board,by the way...

author: drussell
author_rank: Super Contributor
timestamp: February 10, 2021, 07:48:03 pm
content: C131 on the top side next to CN101 is apparently also a semi-common fault.Try that one also if C102 doesn't fix it for you.

author: edy
author_rank: Super Contributor
timestamp: February 11, 2021, 12:19:17 am
content: Thanks for the suggestions. I think the board you are my mentioning is different than my board layout. Is it the power board or the main board you have pictured? I've attached photos of the back of the power supply board. I'll have a look at the main board as well.

author: edy
author_rank: Super Contributor
timestamp: February 11, 2021, 12:31:01 am
content: My apologies... I re-read your post and see now you said it's the main board. I removed it and attached photos. I will solder a cap as you show and let you know where it goes. Thanks again.

author: edy
author_rank: Super Contributor
timestamp: February 11, 2021, 05:39:16 am
content: Ok here is my attempt at following the above example. Tomorrow I'll try it and see what happens! Fingers crossed!

author: edy
author_rank: Super Contributor
timestamp: February 11, 2021, 02:57:26 pm
content: Ok, no luck, same symptoms. Does the 3 red blinks, white light under TV goes on... then as soon as it starts to make the Samsung "chime" sound it shuts down on the first note. I've already placed a 100uF 16V cap across C102. I'll have to swap out C131 as well and see if that works. I've seen some repair kits also like to replace the IC101. Reading some posts on Badcaps.net I see some replacement kits also replacing audio chip IC1203.If C131 doesn't fix it (and I'm thinking to just parallel a cap across it as it will be a bugger to try and remove the tantalum cap as it's a tight squeeze with the iron) then I'm not sure I'll want to start investing more time and money in getting IC101 and IC1203. Hopefully paralleling across C131 will work and the tantalum cap isn't shorted, I'll verify first. I could just be chasing this TV down the rabbit hole.

author: drussell
author_rank: Super Contributor
timestamp: February 11, 2021, 04:23:17 pm
content: Go around checking each power supply everywhere in the unit to see which one tries to come up when the thing dies. There areMANYlocal regulators in most of these units.These kinds of problems are almost always locatable by tracing the sectional power rails and regulators. Whatever section is going active when it dies during initialization is the area of circuitry to check. Sometimes it is non-obvious, or you go down the wrong path by not getting specific and local enough to find the (in hindsight) glaringly obvious problem. It took medaysof messing around to realize where the problem actually was on a few units over the years, like with this Samsung plasma issue, for example:https://www.badcaps.net/forum/showthread.php?t=43075For most people it seemed to be mostly one cheap MLCC capacitor playing up, occasionally IC itself, but once you realizewhat general circuit sectionis at fault, it's usually pretty easy (and cheap) to solve.You still never mentioned before whether when you disconnect the backlight board from the PSU board if the backlight power on the PSU side actually comes up full? If not, pull whatever transistor is driving those transformers on the PSU going to the backlight in case there is a shorted turn in one of the transformers or something. I've seen this several times on LGs with the CCFL tube backlights.If you do suspect it's audio related (it IS playing the chime, after all) it is usually the amplifier section that causes issues and you can just disable the power to it, but if there are common IC issues on these sets, you might be able just hot-air the chip off and see if the behavior changes. You've nothing to lose by hacking up a free "junk" TV. If you at least find out where the problem lies, you can often just grab a used board for $40 as a permanent fix once you know the set is actuallycapableof running if you've hacked up the original board in your sleuthing efforts.