Samsung Syncmaster T240 Power Supply Problem - Page 1
Forum section: electronics / beginners

author: dave_birdi
author_rank: Contributor
timestamp: November 15, 2012, 10:02:45 pm
content: Hi all,First post on the EEVblog forums so I hope you guys can help me out!I have a Samsung Syncmaster T240 24" LCD monitor, manufactured in June 2009. (See below link for specs)http://www.amazon.co.uk/Samsung-Widecsreen-Black-Monitor-Ready/dp/B0017HAR0IRecently, the backlight behind the display had started flickering intermittently during the first few seconds after powering up the monitor.I didn't pay much attention to this up until today when I tried to use the monitor and the backlight would switch on and flicker for about 2-5 seconds and then switch off entirely. Shining a torch at the display would reveal that the LCD panel is still working though.After some Googling it is apparent that Samsung's Syncmaster range is notorious with regards to bad caps and faulty inverters in the switch-mode power supply.I think Dave himself managed to repair some Syncmaster monitors by changing out bad caps.I've cracked open the unit and have taken some photos of the power supply. As far as I can tell, all the capacitors seem to be in pretty good condition, I can't see anything obviously wrong which leads me to think there's an issue with the inverter which supplies power to the backlight.If you guys could take a look at the photos and provide your two cents I'd appreciate it.Many Thanks,

author: dave_birdi
author_rank: Contributor
timestamp: November 15, 2012, 10:14:40 pm
content: Sorry forgot to upload the pictures, D'oh!

author: Thor-Arne
author_rank: Unknown
timestamp: November 15, 2012, 10:48:35 pm
content: You checked the fuse I guess?If you don't have a ESR meter you could just change some of the caps to see if that helps.Thislink has a picture of what caps that is included in a "repair" kit. (They even have a money back guaranty on their repair kits if it doesn't fix it).

author: dave_birdi
author_rank: Contributor
timestamp: November 15, 2012, 11:30:16 pm
content: Quote from: Thor-Arne on November 15, 2012, 10:48:35 pmHi Thor-ArneThanks for your reply. Fuse continuity is good, I don't have an ESR meter but all the caps look to be in good physical condition. I could replace these but I just wanted to make sure that it wasn't the inverter.Power seems to be reaching the LCD display fine so I would guess there's an issue with one of the inverter caps or the inverter itself.Can anyone think of a safe way to test the inverter to see if it's working properly?

author: retiredcaps
author_rank: Super Contributor
timestamp: November 16, 2012, 12:51:45 am
content: Quote from: dave_birdi on November 15, 2012, 10:02:45 pm2 seconds to black can bea) bad capsb) bad ccflsc) bad ccfl wiring (especially the return wiring)d) bad secondary windings on the inverter transformerFor d), your secondaries should be around 940 ohms as perhttp://lcdparts.net/TransformerDetail3D.aspx?ProductID=3696More details starting with post #19 athttp://www.badcaps.net/forum/showthread.php?t=10419Also, see budm's Inverter tester using old CFLhttp://www.badcaps.net/forum/showthread.php?t=19987

author: dave_birdi
author_rank: Contributor
timestamp: December 04, 2012, 10:22:48 pm
content: Hey all;I have replaced the power Inverter with a brand new one, and I have also replaced 8 of the capacitors.I still have the exact same problem, monitor powers up and CCFLs illuminate and then power off after two seconds.:-(Red lines indicate new components:New Inverter & Caps in RedNew Caps in yellow

author: tom66
author_rank: Super Contributor
timestamp: December 04, 2012, 10:29:37 pm
content: Whenever I see a flickering monitor or TV, I immediately suspect the primary capacitor. It is a very common cause.

author: dave_birdi
author_rank: Contributor
timestamp: December 04, 2012, 10:43:27 pm
content: I think the smoothing cap is fine, plus I don't feel too confident probing the thing whilst live to see if there's a steady DC voltage.The LCD itself is still working, from what I can gather this sort of problem is typically down to a faulty inverter or bad caps. It could be the CCFLs but both of these illuminate after being switched on (albeit only momentarily).

author: nukie
author_rank: Frequent Contributor
timestamp: December 04, 2012, 11:10:48 pm
content: A common problem for Samsung flickering backlight is weak opto isolator, check those. The non buldging caps are okay quality you shouldnt need to change them. Not all Samsung PSU has bad caps.

author: notsob
author_rank: Frequent Contributor
timestamp: December 04, 2012, 11:10:59 pm
content: A BAD CCFL will show the 2 seconds to switch off syndrome, if you do not have a way to swap a test ccfl on to your board - look at retiredcaps reference - you can make a few test ones from a box of commercial units ( ie for you house type compact fluoro lights) with a little effort.

author: dave_birdi
author_rank: Contributor
timestamp: December 04, 2012, 11:16:23 pm
content: 1.) Where is the optoisolater on the board?2.) I'll try and wire up a test CCFL.

author: Monkeh
author_rank: Super Contributor
timestamp: December 04, 2012, 11:18:41 pm
content: Quote from: dave_birdi on December 04, 2012, 11:16:23 pmStraddling the white line between primary and secondary sides of the board.Quote from: dave_birdi on December 04, 2012, 10:43:27 pmIt's not going to reach out and stab you in the eye. It's only a few hundred volts. Just keep your fingers behind the guards on the probes and don't cross the streams (err, tips). There's no use being afraid of the thing.You could also just change the cap.

author: Psi
author_rank: Super Contributor
timestamp: December 04, 2012, 11:25:14 pm
content: If you have a spare mains cap lying around you could temporarily solder it across the current one and see if it fixes the issue.

author: retiredcaps
author_rank: Super Contributor
timestamp: December 04, 2012, 11:25:28 pm
content: Quote from: Monkeh on December 04, 2012, 11:18:41 pmAn alternative is to use aligator clips like the ones in the picture. I use them whenever possible for high voltage.

author: Monkeh
author_rank: Super Contributor
timestamp: December 04, 2012, 11:26:36 pm
content: Quote from: retiredcaps on December 04, 2012, 11:25:28 pmThis is good advice. Also, just clip them on before powering up, if you're really deathly afraid 340V or so will come flying through an inch of air and 3mm of plastic.

author: retiredcaps
author_rank: Super Contributor
timestamp: December 05, 2012, 12:19:04 am
content: Quote from: dave_birdi on December 04, 2012, 10:22:48 pmBTW, what tests did you do that led you to change out the caps and inverter transformer?

author: retiredcaps
author_rank: Super Contributor
timestamp: December 05, 2012, 12:21:03 am
content: Quote from: Monkeh on December 04, 2012, 11:26:36 pmYes, I should have mentioned that part of any newbies that may read this in the future.

author: tom66
author_rank: Super Contributor
timestamp: December 05, 2012, 01:35:09 pm
content: I have probed many mains caps, but it always worries me. It may be only a "few hundred volts" but one slip and you complete the circuit.I have only ever done it when a PSU was off, I don't want to know what it feels like when it's energised.

author: Rick
author_rank: Frequent Contributor
timestamp: December 05, 2012, 03:07:41 pm
content: Or alternatively buy a pair of special led strips and a driver board to drive those leds and replace the ccfls with those led strips. It works great.I bought those (the driver board is included in the price of the leds):http://www.merterelektronik.com/LCD-Monitor-Lambasi,LA_2620-2.htmlI tried hard to find one of those on ebay or aliexpress or taobao but I couldn't. If someone knows about it please let me know.

author: T4P
author_rank: Super Contributor
timestamp: December 07, 2012, 06:16:05 pm
content: Quote from: Rick on December 05, 2012, 03:07:41 pmHey rick, try this shop out :http://hmpc2005.taobao.com/category-65584171.htm?spm=2013.1.4010-196790597.30.KekX8u&search=y&parentCatId=35500237They do sell CCFL testers if you are inclined to buy one

author: Rick
author_rank: Frequent Contributor
timestamp: December 07, 2012, 06:47:44 pm
content: That's definitely a nice website. Thanks. If I find non working LCD monitors I shall contact them. The prices are reasonable.

author: dave_birdi
author_rank: Contributor
timestamp: January 07, 2013, 12:58:05 am
content: Well, not too sure what was the fault was but spotted a SyncMaster T240HD with a smashed LCD Scren for £ 10.Assumed that the LCD screens were identical and it turns out I was right.Well, at least I've got something working and my new Monitor has DVB-T support!

author: wrc
author_rank: Newbie
timestamp: December 17, 2013, 04:30:35 pm
content: I had a similar problem with one of my 4 identical SyncMaster T240 monitors, all purchased approximately 4-5 years ago.The image would go off after a few seconds after power on.However, the caps and the power supply board turned out to be okay. It was the burned out high voltage connector to one set of halogen lamps inside the display assembly. One wire became lose. See pictures.I think it could be a common problem, too.

author: wudy
author_rank: Newbie
timestamp: March 20, 2014, 03:40:39 pm
content: Hi there,sorry for necroing old topics, but the last post in here fits to my current problem.Display-Problem:Some days ago my T240-Display started to make weird noises and started flickering. Now the backlight turns off after 2 seconds, while the display still shows the video-signal of the grafics-card.Cause of the problem:After some Google-Researchi assumed this behaviour has probably something to do with a protection circuit detecting a failure with the backlight CCFLs. And yes it was the right guess, after disassembling the monitor i found a burnt connection at one of the backlight CCFLs. Exactly the same problem the pre-poster "WRC" was talking about.Question:Replacing the backlight wouldn't be that much of a task. But i have problems finding a store where i can purchase the corresponding replacement-parts (maybe i'm searching with the wrong keywords). So i decided to ask some experienced guys in this forum. Is there a chance to buy those backlight-ccfls somewhere?Greetings, wudy

author: wrc
author_rank: Newbie
timestamp: March 20, 2014, 06:15:49 pm
content: Quote from: wudy on March 20, 2014, 03:40:39 pmI bought mine at ccflwarehouse.com - they are not exactly the same, but pretty close (I ordered a "Standard Monitor Repair Kit" for for lamp size = 530 mm, 2.6 mm diameter). The "kit" in my case was only 4 CCFL units, without silicon endings or wires, so if you need silicon endings order them separately. You can also order the entire LTM240CT04 panel from China.Hope it helps.

author: dave_birdi
author_rank: Contributor
timestamp: April 02, 2014, 10:27:43 pm
content: Hey there,It's probably worth mentioning that tinkering around with the soldering joints on the CCFL did sort this problem out.I believe this is a pretty pervasive problem with Samsung T240 HD LED Monitors constructed around 2008/2009.