EEVblog #347 - Bad Cap LCD Monitor Repair

[G7PSK]

...but the first time it blew it sounded like a shotgun being fired right behind me.

How do you know what that sounds like?

Well being a former range officer and a shooter mostly clay's these days there has been occasions when I have been very near some firing a shot gun sometimes behind me such as when in a line and I fire to my left and the guy to my right fires forward or such like.

[T4P]

Well what can I do, I was curious, so I couldn't help it... I have opened my SAMSUNG SyncMaster 920N (it had 6700 working hours) and I have found that all electrolytic caps where fine (at least not bulged), and they are Samxon GF(M). So my question, again, is are these caps any good and should I replace them with good quality ones, as a precaution?

http://www.lckdanny.com/samxon/

No good, definitely not . i remember somebody here saying SamXon is samsung's capacitor manufacturing

[Slobodan]

OK, thanks. I have ordered some Panasonic, Rubycon, United Chemi-Con and Nichicon one's (for LCD monitor and for ATX power supply).

[mariush]

No good, definitely not . i remember somebody here saying SamXon is samsung's capacitor manufacturing

No, they're not.  SamXon generally are OK, but the very low ESR ones (GF in particular) go bad often.So you're probably just lucky that it lasted so long, or you live somewhere colder than usual/you have air conditioning set at cold in the house .

Samsung made capacitors and they were Samsung:



but at some point they sold the business or rebranded their capacitor business as Samwha

Samsung likes to use Samwha in a lot of their monitors, because Samwha is also South Korean like them. There was rumor is Samwha bought manufacturing plants from Samsung or something like that, but Samsung advertises Samwha directly on their site so I guess they have something to do with them.

At some point,  some series from SamYoung and Samwha were OEM capacitors made by Evercon... who was previously known as Sacon who were previously known as GSC...  (Sacon FZ series are guaranteed to blow up or die, the nightmare of video cards).

GSC also did Capsun, Comet, Lelon OC-CON...  see  http://capacitor.web.fc2.com/special2.html


At some point, SamYoung also had some partnership with United ChemiCon - that's why their logo was very similar to United Chemi Con's. Later on there was some argument/lawsuit and scrapped the logo:

SamYoung by UCC: 



SamYoung by them:

[Slobodan]

Thanks for the information.

[tom66]

Samsung have had a major issue with Samwha capacitors going bad after a couple of years in their LCD TVs/Monitors (and to a lesser extent their plasmas, though they tend to use the worse C(r)apXons in them, which also go bad.)

LG also used them and got bitten by the bad caps (the first LCD TV I fixed was an LG 42LC46 with four bad Samwha WB caps) but not half as bad as Samsung as LG mostly used Samxon and SamYoung which for some series are good, others they are average or poor.

It seems that Samwha had a major issue with the reliability of the WB and XC series. It seems to have been more of an inconsistency in manufacturing (like the overfilled Nichicon HM/HN's) as I have seen some WB last ages, others die in two years. The caps generally bulge when fail, I've not seen any that just dry up and die.

Older Panasonic plasmas were very well built with excellent caps but I've just seen inside the newer ones - full of crappy Aishi and Taicon caps!!

[T4P]

Right, thanks for clarifying. Poor memory of mine

[samgab]

Well what can I do, I was curious, so I couldn't help it... I have opened my SAMSUNG SyncMaster 920N (it had 6700 working hours) and I have found that all electrolytic caps where fine (at least not bulged), and they are Samxon GF(M). So my question, again, is are these caps any good and should I replace them with good quality ones, as a precaution?

http://www.lckdanny.com/samxon/

Yes, but despite what was said above, have you ever heard the expression "If it ain't broke, don't fix it"? Wait until you have a problem, then fix it.
But on the other hand, there is also the saying "An ounce of prevention is worth a pound of cure" - Benjamin Franklin... So, your choice.

[mariush]

I'm actually on the other side on this one... you should definitely fix it if you have the money to get quality capacitors and are skilled with a soldering iron.

Bad capacitors can do quite a lot of damage to a power supply - it can make transistors oscillate or overheat and die (and sometimes you have a hard time finding replacement ones),  diodes can short... some power supply have zener diodes acting as a sort of protection so capacitors going bad can cause these to trigger and turn the power supply off.

Dave would know a lot more about this and it really sucks Dave didn't have enough time to give some explanations in plain English (or better put Australian) about the role of the capacitors in power supplies.

On my own monitor on my desk, Samsung T240... the backlight starts to ever so slightly flicker, most likely due to capacitors giving bad power to the inverters or the cfl lamps getting old. it's about 2 years old but I certainly won't wait until it dies completely to repair it, it's often more difficult to fix them.

[tom66]

A common issue on Samsung LCD TVs is for bad caps to corrupt the EEPROM (set won't boot if this is the case) which can be tricky to fix.

[T4P]

My Samsung ... LA22A450C1 TV that was a free gift i use everyday as my monitor, first 2 years used quite a bit but i use it permanently since last year.
Hasn't gone awry but when it does i'm pretty darn sure it isn't that bad as normal consumer equipment of the time, this was in 2008 where Samsung was considerably cheap and decent now it's just expensive and nasty

And the TV that was first purchased in question only broke once on the 3rd year just BEFORE warranty, the entire LCD went bust.

[JoannaK]

I'm not sure if I should blame or thank Dave... due this video I decided to order an ESR meter. Thankfully it's not a big investment and I do have hope that it'll pays back on some future repairs/hacks. 

[Pat Pending]

Does anyone know why the connection to  the driver PCB to the LCD panel is by individual wires as opposed to a ribbon or flex cable?

[tom66]

They sometimes do it with ribbon flex too, my 24" 1080p monitor uses a flat flex ribbon but it's kind of rare. It probably depends on the signal speed, EMI requirements, cost, etc...

[Pentium100]

Does anyone know why the connection to  the driver PCB to the LCD panel is by individual wires as opposed to a ribbon or flex cable?

The cable seemed to use twisted pairs. While it is possible to have a twisted pair ribbon cable (I have a couple U320 SCSI cables that are like this), individual pairs are probably cheaper.

As for caps - the ones that operate on the line frequency rarely go bad, unless they were made in late 80ss early 90s in the USSR. Those dry up and look completely normal but are essentially an open circuit.

[ebidk]

There's a problem with the Samsung SyncMaster 226BW where the backlight flashes.

The power supply board looks very similar if it's not actually the same one. It can be fixed by replacing 3 capacitors.

I have a post about it, which also link to a post with pictures of the rest of the boards in the 226BW.

[SeanB]

I have a new victim/patient from work today. 30 odd kilos of 24 inch Samsung Syncmaster CRT, DOA, but with the power light on. Will be stripped sometime when space and time is available to see what is wrong, or what died and stopped it working. Good life for this one, made in 2002, and on 24/7 for the most part since then, though there was a DPMS power switch that did work for the most part.

[Chipguy]

Yay Dave you are so lucky
In both cases the little green fuse was still ok. I had to replace them when mine failed as well.

Good work !
Chipguy

[sonic]

On my SyncMaster 244T, the green power LED was only dimly lit. I also successfully replaced all caps (excluding the 400 V one) on the PSU in it and other gear. I documented my ESR readings here.

When replacing caps in a PSU you should also replace the low-voltage one on the mains side - this is for the startup supply and a common cause of failure as on initial  startup the supply comes through a high value resistor, and even a small amount of leakage on this cap can prevent the PSU starting.

This happened to me with the Jentec JTA0302F-E PSU that D-Link liked to use often.

[dda]

So,  what is a low-esr value (ohms) compared to a not low? What kind of esr should i be looking at when im capacitor shopping?

[mariush]

Look in the datasheets for impedance below 0.04-0.06 ohm .... the capacitors with such value are low esr... ultra low esr i'd say would be 0.006-0.025 ohm  - but be careful, as some circuits are designed to have some impedance, they won't like ultra low esr capacitors.

Also look for the amount of ripple current  they can handle - you want the value listed at 100kHz or anything above 10 kHz at a positive temperature ... if the datasheet only lists 120Hz or some low frequency, that's a sign those capacitors are not suitable for switching power supplies or other high frequency stuff.  You want a value as high as possible.

Last, look at the temperature rating, make sure they're 105c and ideally 2000 hours or better - lcd monitors can be quite hot in the back, so you want capacitors that can handle heat well.

Oh... and don't forget to check the diameter and height - you want capacitors that fit in the room you have and not touch the lid and cause shorts or other bad things.

For a 470uF 25v like Dave has in the monitor, you're looking for something with at least 800mA ripple and about 0.04-0.06 ohm impedance - something like Panasonic FC series would fit this and would be the lowest from Panasonic I'd use.
For a 820uF 25v, something around 1200mA and 0.04 or lower impedance would work.

Good brands and series for monitor fixing would be (imho, i may be wrong with some, not really an expert in this): 

Panasonic FM, FR, FC (in worst case),
Nichicon HM, HD, HE, 
United Chemi Con KZE, KY , LXZ ,
Rubycon ZL, ZLH, YXF , YXJ etc

[JoannaK]

On my SyncMaster 244T, the green power LED was only dimly lit. I also successfully replaced all caps (excluding the 400 V one) on the PSU in it and other gear. I documented my ESR readings here.

When replacing caps in a PSU you should also replace the low-voltage one on the mains side - this is for the startup supply and a common cause of failure as on initial  startup the supply comes through a high value resistor, and even a small amount of leakage on this cap can prevent the PSU starting.

This happened to me with the Jentec JTA0302F-E PSU that D-Link liked to use often.

I think I'll need to check couple chepish Digibox power supplies nearby.. Those have the most mysterious startup-problems.

[stryker]

Thanks for the inspiration and explanation Dave.  I found an LCD monitor on top of the dumpsters under our building last week, by luck a Samsung with no power but a different model.  Found the caps in that part of the power supply board were in some cases swollen, but not yet leaking.  Took the punt and replaced them and can report a successful first dumpster dive!

Bad news is while I've 'made' a monitor for $5, it has a fault in the LCD that shows a full height vertical single pixel line near the right side.  Nevermind.  Was a good exercise and it's something I wouldn't have tried without seeing your vid.

Please keep em coming !
Geoff

[Ed.Kloonk]

stryker stryker stryker stryker!

[bongiovi]

I just fixed my Samsung by replacing the bulged Capxon.  I replaced it with a smaller sized cap but with the same Farad and Voltage.  I then saw some posts that says different sizes probably mean different ESR (whatever that is). 

The monitor now works, but is it ok if I just leave it like that without checking the ESR?  Assuming the ESR doesn't match, can somebody explain to me in plain English the consequences of a mismatched ESR?

Thanks guys.