LCD Monitors failing, Bad Caps?

rwgast_logicdesign

Ok well let me say first of all there is bad caps in the monitor im looking at there all puffy! But im not sure if its the main issue.

Anyways today I went to get a glass of water came back and my monitor had a red vertical line down the left side!! I looked on google some people said that happens when the amplification chips go bad but im not sure about all that.. anyone know what causes this, it definately the monitor the line stays when the vga cable is unplugged.

So I had another monitor I got from a friend that was better anyways. He got it from me along time ago it worked fine! He said within two weeks it just wouldnt turn on. I flipped it on and it came on but it looked like half the pixels were dead literally half or more... I know the major symptom of bad caps is the power supply just not working could it still be the caps causing this dead pixel like problem? The caps are bad for sure 4 out of 6 25v 470uFs are puffy and one 220uF is swollen! I was gonna order some decent panasonic caps and replace all the power supply caps in this monitor. Does it sound like theres more going on than the caps? I cant really afford a new monitor right now but I can afford a few caps so Im hopping this isnt a problem with acuall dead pixels. I had another friend with this exact monitor and it developed a huge black patch of dead pixels in the corner maybe the size of half a dollar bill, just happened over night.

xanadu

Bad caps could definitely cause that, you have to fix them to continue troubleshooting the pixel issue anyway. Don't you hate bad caps? This is based on replacing a lot of bad caps. It's hit and miss, like 75% are success, 20% fail shortly after, 5% fail a year or so later.

If the caps are not low ESR then it probably just the caps. If the caps are low ESR it can still be the cap but is less likely you'd have more than one go bad.

If there are any inductors around the caps check the film over the visible part of the coil and if there is discoloration. Check the entire board with a magnifying glass and visually inspect every component. Sometimes caps bulge from the bottom and the top looks normal. If you see anything else on the board discolored or burnt then it is probably not the caps.

Make sure you monitor it after you replace the caps, I would suggest leaving it powered off (better yet unplugged) when you aren't around for at least 100 hours of use.

rwgast_logicdesign

well like i said there are definatley 6 bad puffy caps total, and im gonna order some panasonics that have like millaohm esr ratings. I was just a bit scared that the acuall lcd may have dead pixels. There is an inductor its wrapped in heat shrinking should I take that tubing off and check it?

xanadu

Probably not worth removing the heat shrink. Check the edges of where the heat shrink is cut for discoloration. Replacing the caps and a good 'non-invasive' visual inspection is usually all I can do. I've had a lot of workstation/home PC motherboards with bad caps. With LCDs I have had a lot that had bad caps but, some with inductors that were burnt looking. In fact a couple of times someone I knew took it apart and said it needed capacitors and then when I saw it the component in question was an inductor. I try to keep safety in mind and when stuff is burnt, especially laptop motherboard DC jacks there is usually a waiver involved.

It's a long shot but you can also test the failed caps for a short. I don't know if caps can fail closed, I should probably find out. It's seems if one did it may damage other components.

Can you take a pic of the pixel issue and post it? Usually dead pixels don't group up unless there is a connector issue or physical damage. When computer video cards go bad you get some artifacts that make it look like your monitor has gone mad. I've seen cards that artifact that you could fool anyone into thinking the LCD was bad haha. Bad power supply could cause that all to happen but I'm interested to see the actual bad spot in action.

rwgast_logicdesign

hmmm well the thing is apart in the garage at the moment i need to soilder a regular power cable to it also damn 3rd party plugs. I will see if i can get it to come on again and take a pic when i put the new cable on but basicaly it looks like diagonal tear more horizontal than vertical the line is kind of like jagged mountains everything below is dead everything above works is basically how i remmber from the last time i tested, although the previous owner said the power led wouldnt even come on

Gadgetman

Vertical lines often indicate an error in one of the driver ICs along the edge. On laptop screens this is considered 'fatal' as they're very difficult to replace.
On desktop monitors, I don't know...

It can in some cases be caused by a bad connection to the panel itself, but fault-finding this without causing additional damage is just about impossible.

Tymkrs

Whisker's monitor wouldn't even turn on let alone have a few bad patches. I'd replace the caps as those don't cost anything compared to a new monitor, and see. He's replaced his and his monitor works better now than before

LoopyByteloose

No reason to leave puffy capacitors in place if you are doing a repair. This may only be the first step, but it is a needed one and if you later abandon the repair you are not out a whole lot of money.

I have a little TV box that converts cable to my VGA. It failed and was very hot. I checked the caps and they looked bad. So I replaced all AND increased both the quality and the high voltage tolerance of them to assure long life. With voltage regulators or switchers involved, you should not mess with increasing the microfarads, but you can do some enhancements.

The little TV box works fine now and has for over a year. Replace ALL the electrolytics, not just the puffy ones as others may have failed or are near failure as well. Visual inspection is not enough to decide good or bad.

I would not bother with a lot of research until after I got the caps replaced and saw how the monitor behaved. Digital devices can just be too quirky due to bad power.

If problems persist, I would use a spray tuner cleaner to remove any dust or carbon build up on the circuit boards. That is a big air pollution problem where i live and I have had to clean one monitor about once a year as carbon in the air from steel mills shorts the fine pitch leads on the chips. You can confirm it is dirt by slapping the side of the monitor and seeing it start to behave normally for a while. The slapping shakes the dirt loose for a few seconds.

More recently, I replaced all the push buttons on my 5 year old air conditioner as they were no longer working right. These are cheap parts as well and amongst the first to go. Before their replacement the a/c was behaving very oddly due to the microcontroller being confused, now it is fine. Shops wanted me to buy a new A/C as it just had its warranty period end.

RDL2004

Use at least 105 degree rated capacitors as replacements, even if the originals were 85 degrees.

rwgast_logicdesign

Ahh thanks RDL I had my digikey order saved just looked over it and realized my 470uf choice was only 85 degree. I went with panasonic caps that had the same physical deminsions and had either a low ESR or low input impedance rating listed on digikey. I think I should be safe the originall caps were 85degree xunda brand...

xanadu

Here is my logic on not using caps that are higher rated than you are replacing, with the exception of tolerance and lower ESR.

For an over-voltage situation the cap fails open and nothing gets fried, it is like a cheap surge protector. If there is an issue with high voltage the higher voltage cap will no longer fail, something else will. I'd rather have a cap fail.

Same for temperature issues. If it's that hot it there then something else is wrong and it will need to be addressed.

RDL2004

Except that the operating life of an electrolytic capacitor is directly affected by it's temperature rating, the higher the better.

When the capacitor is operated at temperatures other than the maximum rated temperature for the
capacitor the expected life of the capacitor will increase. The rate of increase in expected operating life is
for the life to double for every 10°C decrease in temperature.
The above is expressed mathematically as:

L2 = L1 * (Vr/Vo) * 2^x

Where :

L2= life expected at ambient temperature.

L1= Load life rating of the capacitor.

Vr= Rated voltage of the capacitor.

Vo= applied voltage

X = (Tm-Ta-Tr)/10

Tm= maximum rated temperature of the capacitor.
Ta= ambient temperature.
Tr= temperature rise due to ripple current

from "Reliability of Capacitors", by Illinois Capacitors, Inc.

of course, if it would last long enough for you with the lower rating then all is good anyway.

xanadu

The point was that it may not be desirable for them to last longer.

Don't you think that if you beef up a failed part, and there is a problem other than that part, now that beefed up part will not fail, something else will? Maybe it is just me lol...

To me it is like saying I cannot run 15 amps over a 10 amp fuse, so I'll make it better by putting in a 100 amp fuse. I know a cap isn't a fuse but still...

LoopyByteloose

Using 105 degree rating to replace 85 degree rating and higher voltages are not likely to cause other things to fail PREMATURELY. But something will always end up failing.

Theory about having the cap fail rather than something else is rather dubious. Where is this higher voltage suppose to come from? And does the failed cap always do not harm? Sure, you can always argue lighting strikes, but if the unit is really protected that should not be an issue. If it is an issue, maybe nothing can protect the device unless the manufacturer has actually included the new scheme of MOVs and fuses together.

If the cost is no more, just buy to higher spec replacement. I usually do this with everything I keep on hand. It seems that caps of good quality have been evolving into smaller and smaller packages, so they can fit in where they may not have in years past.

The main point of the upgrades may be that the manufacturer actually creates a warm environment and puts in caps near to failure voltages so the unit has a shorter useful life. Most of the components on a circuit board will just run nearly forever if given a chance - but the electrolytics and the switches are the weakest links and the first items to go due to age.

The only device I've been unable to revive by replacing failed caps has been a regular computer motherboard. I suspect that the complexity of multiple voltages inside the CPU may have gone haywire.

rwgast_logicdesign

i think he was saying higher voltage caps are a good idea as they provide more smoothing when transients and voltages go a stray

hi temp caps arent becuase if the monitor is getting hot enough for the caps at the correct rating to fail something other than the caps needs to be addressed, at the correct raiting caps ideally shouldnt overheat. which raises the question the hige 100uf 400v cap had white epoxy holding it on the boared in a fixed horizontal posistion, was that thermal i see it on some resistors too.. cuz i dont have any thermal epoxy only paste and unless digikey has it for under 5 bucks im not buyin any ill just use the best temp raiting i can get.

heres my outlook if i user higjer caps ill get more lofe if the manufacturer went as tight on the spec as they could (im assuming its so the brand is already bad so they probably didnt up the caps to save a few more cents) uping them will help especially since it gets to 120 here. if something else is wrong and is causing the problem i probably cant fix so might as well make it work till it goes dead!
No

RDL2004

higher voltage caps are a good idea as they provide more smoothing

The voltage rating has nothing to do with their "smoothing" capability.

the hige 100uf 400v cap had white epoxy holding it on the boared

This is done to secure the larger capacitors to the board mechanically. This keeps the stress off the solder joints.



A few things you need to keep in mind...

Electrolytic capacitors have one of the highest failure rates of any electronic component and the primary cause of their failure is heat. Electrolytic capacitors have a relatively high cost for passive components and manufacturers of electronic devices are always looking to lower their costs. Capacitors rated for 85 degrees are cheaper than 105 degree rated capacitors. Many manufacturers only care if their product makes it to the end of the warranty period.

Also, it isn't necessary to run an electrolytic capacitor at or above it's temperature rating to benefit from a higher rating. See post #12 above.

xanadu

Look it's my way, or the highway! Haha. Thanks for the input, let me just say a few more things because I agree with you and it sounds like I don't, here is why.

Basically, I do what I do (replace caps only upgrading ESR) because I am not highly skilled or trained with electronics. I have no idea what is going on in the circuits these caps are attached to. I'm definitely not trying to talk anyone out of experimenting with better caps, by all means do so. If I were to replace caps on my own gear, sure I'd consider making changes. The problem is my stuff never goes bad hahaha.

I have an issue with modifying hardware in people's businesses, I try to keep it as OEM as possible. As bad as it sounds, I'd rather stick to what the manufacturer put in there with the exception of the ESR rating. It's a matter of liability to me. There are too many unknowns. If I were to modify a board that much I'd need to hold it for lots of stress testing before I felt comfortable giving it back.

I hope this doesn't give you an unsettling view of how I do repairs lol. If the new low ESR replacement caps fail again I tell the person there is nothing I can do, issue a 50% refund, and they know all that before any work is done. Works well for me, literally no complaints over 8 years across the board for any repair of that type.

LoopyByteloose

The voltage rating is a failure level. Electrolitic caps are notorious for a very sloppy fit to specification - so if your engineering were to say use one at a 16V rating, I'd use a 25V. It is about the level of insulation and ability to not short out. It doesn't hurt to use a 50V rating to replace a 16V device - but the capcitor might be too large to fit in the space. In a pinch, I have used 400V rated device for a 5v circuit.

Since electrolitics are rather sloppy, a 16V device may barely be able to handle 16V and age faster to something less.

Heat is always the big destroyer of electronic components, so devices that can handle more heat are always better even if they are never exposed to higher levels of heat.

BTW, I am not in the repair business. If I fix it, it is a freebie for someone and no promises that it won't break again rather soon. Old stuff is old and often has more than one problem area. I once replaced a water pump for a girl on her car and soon after her clutch went out and she never believed it wasn't my fault. Repair customer can be impossible at times.

RDL2004

Just to be clear, I'm not suggesting that every cap should be of the highest possible temperature rating. Many devices never get much above ambient temperature and 85 C is 185 F. However, where there is heat being generated (power supplies, monitors, etc.) and there has already been a failure, it just seems like a good idea to me.

LoopyByteloose

I'll stick with my thesis -- if the replacement cost and physical configuration are the same, try to get all the practical improvements you can. These improvements may not be required, but the product has been developed to be more durable.

And yes, 85 degrees centigrade is hot, 105 degrees centigrade is painful hot, maybe melting thermoplastic.