EEVblog #347 - Bad Cap LCD Monitor Repair

[EEVblog]

 

Dave.

[mariush]

No surprise there.

Capxon is very well known manufacturer for making capacitors that don't handle heat. They all die eventually.

ps. that one is probably from Mexico or somewhere that's NOT South Korea - the ones they assemble in Korea are usually made with Samwha capacitors - just as bad as Capxon imho.

ps2. watched to the end... those S.I capacitors are worse than CapXon ... I don't think they'd last more than a few months if the monitors run several hours a day. I'd recommend replacing them as soon as possible with some United Chemi Con / Nichicon / Rubycon capacitors.

[nicknails]

I would have just replaced them all since I was in there anyway.  No point in taking it apart twice!

[Rerouter]

always fun getting near freebies just because of a blown cap or 2, even to the extreme of them failing in 30 year old test equiptment, still its sometimes hard to justify the cost of replacing all of them with top quality caps

also whats people opinion on not only getting higher temperature /life capacitors but also higher voltage for replacement?

[EEVblog]

I would have just replaced them all since I was in there anyway.  No point in taking it apart twice!

Not when I don't have good brand ones to replace with.
I just needed them up and running for the show on Tues.
I wasn't about to pay $7ea for no-name 400V caps.

Dave.

[David_AVD]

Well done Dave.  A nice simple repair but satisfying because it only cost you a few bucks in parts.   

The main filter cap is rarely faulty.  Almost always the only issue is the low voltage side.

[EEMarc]

I wonder who got the big bonus for that decision...

[jaycee]

Seen this so, so many times in all sorts of things...
The line side is usually OK because it doesn't have to withstand a lot of ripple current, it only sees 100-120Hz from rectified mains. On the output though, they're seeing kilohertz from the SMPS output. This is where low ESR is a must.

CrapXon ones just obviously aren't - i'd go so far as to accuse CrapXon of LYING on their spec sheets. They can't withstand the ripple current and they blow their guts. If you're lucky, a well designed power supply sees the failing caps as shorts on the outputs, and turns off. Similar story with pretty much all the other Chinese brand capacitors. The big names - Nichicon, Rubycon, Nippon Chemicon, BC Components, Panasonic etc... no problem.

If you're unlucky you end up with major damage. I have a monitor where popped CrapXon capacitors unfortunately also took out the MOSFETs and control IC in the backlight circuit. Similarly I have an LCD TV where capacitor failure in the PSU seems to have damaged something on the mainboard, as even after replacing the caps and verifying the supply itself is working correctly, there's no sign of life.

[Psi]

Yeah, the mains filter cap is only 50hz and has bugger all ripple current compared to the switchmode caps which are probably 200khz with massive ripple current.

It's the ripple current which kills them.
When a manufacture decides to use dodgy caps they often put more caps in parallel and have a bigger total capacity than the design required, just to get a lower esr and higher ripple current.

So when replacing crap 0.5A ripple current caps with awesome 6A ripple current polymer electrolytic caps lowering the capacity value a bit is ok.
Never lower the temp rating or voltage though.

Also,
I was waiting for Dave to either short that big 450V cap with a screwdriver or accidentally touch the pcb and get zapped. Since it didn't power up the cap was probably still charged.


When fixing appliances with bad caps its far far better to get it done before the device fully dies.
Normally you start to get ripple and noise on the screen image as the caps start to fail. So you get some warning.
Often, if the caps get so bad that the device wont even turn on, the switching mosfets short out and die, which then shorts the gate to vcc and often takes out the gate driver and a few other things.
So it can be lots components to repair if you leave it too late.

Luckily in this case they look to have designed the lcd so bad caps dont blow up other stuff.

Edit damn, jaycee bet me to it for most of that.

[JoannaK]

Dave, you mentioned the ESR meter you have.. Would be nice to see it on video and to get some examples of good/bad caps with it..

[Fir3Chi3f]

Had mentioned elsewhere that I made a tutorial for cap replacements, so thought I would link ya to it!

http://www.overclock.net/t/1076808/fir3chi3fs-new-indepth-capacitor-replacement-monitor-repair-tutorial

Another great video! I feel that most of what I know about electrical engineering has been learned from you Dave! 

[samgab]

You asked about service menu over on the youtube page.
I found this, written in Chinglish:
http://www.fastrepairguide.com/monitor-and-lcd-monitor-problem-solutions/login-factory-service-mode-samsung-lcd-mo-2.html

Worth a try, you may be able to find out how many hours those monitors have done, and maybe report back to us interested punters? 

[gxti]

Definitely something about that particular generation of SyncMaster LCDs. I bought a smaller version for my mom for Christmas a few years back, and it failed maybe a year ago. Recapped with UCC 105degC caps, no problems since! Thanks, dickhead from the purchasing department, for giving me that rewarding experience.

[David_AVD]

Better than the Benq's though.  The caps go bad, chopper IC (or FET?) goes bang and they're often a write-off.

[SeanB]

Samgab, thanks for the service menu guide. Mine has done 6700 odd hours, and been turned on 4700 times, with 9 power cycles........ Not bad for a 2 year old display.

[mikeselectricstuff]

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.

[hans]

I fixed 2 Samsung 940BF last summer that had a faulty backlight driver. I think it's around the same age, the construction is very similar (annoying clips on the front size, annoying mouning of the shielding - the 940BF was even more annoying that it had the PCB boards on the backshield plate, and some cover plates to protect the HV outlets, isolation paper on the back).
In my case I had 2 monitors from the same batch, same age, similar use time (well , 1 failed first - had more hours on it, used the second one, which failed 2 months later).
And ofcourse it were those bloody caps! Same capacitance, same voltages, probably same PSU design. I only replaced the dodgy caps with quality low ESR 105C ones from Farnell.

Can be a quick job though, if you're familiar with the model. The first one took longer (going to farnell etc), the second one 15 minutes.

[tom66]

Brand name caps aren't expensive from DigiKey.

I have however seen the line cap fail on several monitors, none belonging to me (all on badcaps.net.) Samxon and Capxon line caps tend to fail with gunk coming out of one or the other terminal. On a monitor with PFC, this usually results in a dead switching MOSFET, diode, and blown fuse, all because they tried to save a few cents... I hate Samsung products now, they have nice pictures when working but they never last, unless you fix them by replacing the caps and other insufficient components they cut back on.

[poptones]

Back in the day when it was still common to find large surplus lots on ebay, I made so much money buying large lots of decent quality electros and reselling them in motherboard sized batches.

[Ed.Kloonk]

As a result of so many bad caps, there are full replacement kits available for computer motherboards. You just specify the board model number and often there is a bag o parts packed just for you.

[IanJ]

As a result of so many bad caps, there are full replacement kits available for computer motherboards. You just specify the board model number and often there is a bag o parts packed just for you.

Same here in the UK........there is an abundance of cap kits available for SKY set top boxes.
Lost count of the amount of boxes I've fixed for friends n family................but the thing is, every time they come out with a new model of box the same issues remain. It's a conspiracy, they design the boxes to last a couple of years only I reckon.

Ian.

[tom66]

As a result of so many bad caps, there are full replacement kits available for computer motherboards. You just specify the board model number and often there is a bag o parts packed just for you.

Same here in the UK........there is an abundance of cap kits available for SKY set top boxes.
Lost count of the amount of boxes I've fixed for friends n family................but the thing is, every time they come out with a new model of box the same issues remain. It's a conspiracy, they design the boxes to last a couple of years only I reckon.

Ian.

The Samsung and Thomson boxes are rubbish and have bad cap issues.

The older (and possibly newer) Amstrad boxes are very well built. I took one apart - full of Rubycons!

[amyk]

Possibly interesting trivia: That Genesis SoC contains an embedded 80186 processor.

Rather surprising when I found that out (several years ago), as most monitor SoCs are based on the 6502 or 8051.

[Ed.Kloonk]

Possibly interesting trivia: That Genesis SoC contains an embedded 80186 processor.

Rather surprising when I found that out (several years ago), as most monitor SoCs are based on the 6502 or 8051.

This is interesting.

[Ed.Kloonk]

As a result of so many bad caps, there are full replacement kits available for computer motherboards. You just specify the board model number and often there is a bag o parts packed just for you.

Same here in the UK........there is an abundance of cap kits available for SKY set top boxes.
Lost count of the amount of boxes I've fixed for friends n family................but the thing is, every time they come out with a new model of box the same issues remain. It's a conspiracy, they design the boxes to last a couple of years only I reckon.

Ian.

The Samsung and Thomson boxes are rubbish and have bad cap issues.

The older (and possibly newer) Amstrad boxes are very well built. I took one apart - full of Rubycons!

I had either a samsung or HP monitor, sorry I really can't remember which, that had a known fault of a poor sodder joint around one of the components in the psu. I googled the problem, found it was quite documented. Opened it up and sure enough, bad joint. A little sodder and I was away.