Bad caps often a symptom, not a cause

[dumpystig]

Since joining BadCaps.Net I've read plenty of threads where a device malfunctions, the owner opens it up, spots bloated/bulged caps - in most cases probably the most obvious sign of a faulty component - and automatically replaces said caps. Then after reassembling it all they are surprised/bemused/pissed that it doesn't work and the original fault is still present.

In my experience I think that caps often degrade and break down over time but whilst still serviceable a different fault develops. So a visual check leads to automatic cap replacement but no investigation of any further possible cause(s).

For example I recently replaced 8 caps on a monitor power board (https://www.badcaps.net/forum/showthread.php?t=17913) even though none of them showed any visible signs of damage, but the original fault remained. After further investigation/testing/head-scratching/cat-kicking followed by a total reflow of every device/pad I once again had a working monitor.

So maybe we should not automatically think we have the problem solved once the visibly fried caps have been replaced, but also think about the possibility of more work troubleshooting to get the device fixed.

And the cat's fine. It really is. Honest.

[dumpystig]

Re: Bad caps often a symptom, not a cause

TC, you may want to move this thread to the General Electronics section.

My bad...

[ratdude747]

Re: Bad caps often a symptom, not a cause

well, a bloated cap is never a good cap, so fixing bad brand caps is at the least a start.

[dumpystig]

Re: Bad caps often a symptom, not a cause

Yeah, that's correct ratty, but I think you've maybe missed my point?

[ratdude747]

Re: Bad caps often a symptom, not a cause

Yeah, that's correct ratty, but I think you've maybe missed my point?

well, troubleshooting always applies...

from the thread title, i was under the impression that the idea was that bad caps do not cause issue but are the side effect of issues. Which IMHO, is absurd, since it is well documented that bad caps can and have in the past caused issues.

rereading the OP, yeah, i see the point, which is that bad caps are not the only thing that can cause issues.

now, there are cases where bad caps are both the root cause of failure and a symptom... USFF boxes and imac G5s come to mind... poor cooling and high temp CPUs do not mix... bye-bye lytics!

[dumpystig]

Re: Bad caps often a symptom, not always a cause

rereading the OP, yeah, i see the point, which is that bad caps are not the only thing that can cause issues.

now, there are cases where bad caps are both the root cause of failure and a symptom... USFF boxes and imac G5s come to mind... poor cooling and high temp CPUs do not mix... bye-bye lytics!

You got it now pal.
I've ammended the title to make the topic clearer.

Edit: No I haven't, can't edit the OP now....

[PCBONEZ]

Re: Bad caps often a symptom, not a cause

Since joining BadCaps.Net I've read plenty of threads where a device malfunctions, the owner opens it up, spots bloated/bulged caps - in most cases probably the most obvious sign of a faulty component - and automatically replaces said caps. Then after reassembling it all they are surprised/bemused/pissed that it doesn't work and the original fault is still present.

In my experience I think that caps often degrade and break down over time but whilst still serviceable a different fault develops. So a visual check leads to automatic cap replacement but no investigation of any further possible cause(s).

For example I recently replaced 8 caps on a monitor power board (https://www.badcaps.net/forum/showthread.php?t=17913) even though none of them showed any visible signs of damage, but the original fault remained. After further investigation/testing/head-scratching/cat-kicking followed by a total reflow of every device/pad I once again had a working monitor.

So maybe we should not automatically think we have the problem solved once the visibly fried caps have been replaced, but also think about the possibility of more work troubleshooting to get the device fixed.

And the cat's fine. It really is. Honest.

Sure, other things break too. - DUH!
Sure, other things can break caps. - DUH.
- But more often bad caps break other things..
.
Lytic caps are a roll of foil submersed in a chemical solution that breaks down for any number of reasons and they are far from being any kind of solid state device.
.
Lytic caps are by far the most failure prone device in electronics.
.
- And that's not new news. It's been like that since tubes.
.

[dumpystig]

Re: Bad caps often a symptom, not a cause

Hmm... Yes, I know all that but it seems a lot of other people don't - the first thing they see upon visual inspection may be bloated cap(s) and then think that replacement will surely fix it. Then on reassembly the fault is still there. As the first paragraph says in my OP I'm seeing a lot of threads where this is the case.

[PCBONEZ]

Re: Bad caps often a symptom, not a cause

That's because there are a lot more threads about screens and screens are built to fail.
They want to sell you another one every 2 or 3 years to keep their business growing.
If they don't sell more next year than they did this year their investors won't be happy.
~ It's essentially all about Corporate interests and Wall Street..
.
If you see bloated caps - they need replaced before you do much else.
Caps often ARE the only problem.
But anyone that thinks that's -always- the only problem is simply inexperienced.
.
I see A LOT of new people dabbling in DIY repair.
[I see people replacing caps that don't even own a DMM yet.]
Thinking new caps is the -only- thing -ever- needed is just a naive newbie mistake.
.

[tuk]

Re: Bad caps often a symptom, not a cause

Hmm... Yes, I know all that but it seems a lot of other people don't - the first thing they see upon visual inspection may be bloated cap(s) and then think that replacement will surely fix it. Then on reassembly the fault is still there. As the first paragraph says in my OP I'm seeing a lot of threads where this is the case.

I'm a complete newb when it comes to electronics but I'l throw my 2 cents in anyways ...I bet there are significantly more cases where following the initial advice( replace the caps ) results in a successful repair than not ..veterans give this advice almost as a necessary first step of the diagnostic process to rule out the obvious ..its a numbers game ..electronic equipment is complex by nature and impossible to be 100% sure about anything unless you can swap the part out ....anyone who doesn't understand this fundamental fact should probably not be tinkering with 'lethal voltage' systems to begin with

[PCBONEZ]

Re: Bad caps often a symptom, not a cause

Exactly.
You pretty much HAVE to have good caps or you can't check much of anything else.
.
How you gonna get good voltage readings with open and/or shorted caps on the board?
Why even try?
...
So replace the caps and hope you get lucky.
.

[smason]

Re: Bad caps often a symptom, not a cause

If you see bloated caps - they need replaced before you do much else.
Caps often ARE the only problem.
But anyone that thinks that's -always- the only problem is simply inexperienced.
.
.

Yup. Whenever I fix a monitor, if there are any bad caps, I replace them all.
Then I test, and always have the meter handy as I expect there to be other problems, though I'd say 80% of the time it's just caps.

[Uranium-235]

Re: Bad caps often a symptom, not a cause

yup, caps are a 'wet' component, chemical based, and are prone to failure before other ones. Sometimes they can go out of spec, and fry other components, before completely failing themselfs-cause they're used in power filtering

[dumpystig]

Re: Bad caps often a symptom, not a cause

A lot of these posts are irrelevant though... I was merely making an observation, going off what I see in a lot of threads here. It wasn't intended to be a discussion on the composition of caps.

[severach]

Re: Bad caps often a symptom, not a cause

We get spoiled because so many products spring back to life once the caps are replaced. This does not happen by accident. The SMPS chip designers have made all the application circuits into which they fit then add smarts to the chips to cover for all the components in the circuit that could fail. Not just capacitor failures, but as many components and as many ways as they can break. Then they publish designs and guidelines for adding external parts to detect more faults and custom faults that silicon smarts alone can't. For the application design to be as safe as the chips are designed to be requires that the application circuit designer meet or beat the quality of the sample designs. If they save a few nickels and leave a few components out or uses a suboptimal chip with lots of poorly stress tested custom circuitry like the AL2416W then you get an SMPS chip that burns stuff out when the most likely of parts go bad.

The Acer AL2416 regularly burns out one or two MOSFETs when the supply capacitors go out. Other monitors that use better SMPS P-N or N-N driver chips don't have this problem. Fortunately the Acer problem has been worked out so we know how to fix it. Some bad designs like the Dell GX280 burn out parts like the Southbridge we are unwilling to replace.

There are places where bulged caps are just a symptom. The Scepter X22WG-Gamer power supply gets much hotter than you can touch. It's just bad design. A fan could solve it. Better air flow guidance is probably what it needs. The el-cheapo original caps had no chance. I shouldn't need to use ultra high grade caps but that's what it takes to keep it off the bench every month. Those will be lucky to make their 2000 hour lifespan.

Sometimes poor workmanship converts one problem to another. Caps are fixed but weren't soldered in right or some other part was damaged. The caps aren't at fault here. Newbies don't have the experience to know where to look for problems they caused.

The number of bulged caps that don't cause failure is vanishingly small because very few caps can maintain specs while bulging. Many of us test the failed caps so we know whether they were the cause of failure or not. Failed caps must be replaced or nothing else can be diagnosed, hence, replace the caps is the most common recommendation. It's also easy and cheap.

[dumpystig]

Re: Bad caps often a symptom, not a cause

I can only repeat what I already stated; even though there may be faulty caps on any particular board they are not automatically the cause of a fault - sometimes they are a symptom of another cause. And moreover, also there are a lot of examples amongst the threads here where all caps have been replaced and the original fault remains. Which was the original point of this thread.

[PCBONEZ]

Re: Bad caps often a symptom, not a cause

Yeah,
And there are cases of blown Rubycon.
And there are Fuhjyyu that last 10 years.
.
And, that I know of, -no one- has ever said caps are the 'only' possible problem or the 'only' possible cause.
- So no one disagrees with you.
In fact I think you're revelation has always been blatantly obvious to most people.
IOW: It's not news...
.
.
Fact remains that caps are the highest failure rate part in electronics.
They are always high [if not #1] on the 'usual suspect' list.
And it's been like that since they were invented.
.

[bluerobboman]

Re: Bad caps often a symptom, not a cause

Having read all of the posts on this subject and at the risk of being accused of sitting on the fence basically you are all right! Yes just changing any suspected capacitors and expecting 100% success is foolish. However having been in the industry for almost 40 years the basic principles have not changed since valves or vacuum tubes as some say. I was always taught to repair / establish correct psu voltages before proceeding to the main circuitry this is particularly important in say dc amplifiers, long tailed pairs etc. and as for the "blind replacement of bulging capacitors is the same would you leave a "suspected component in a circuit under repair no of course not! My method is to find / eliminate all the "no brainers" such as dry joints, bulged caps, burnt / heat stressed components etc and as already mentioned this often cures say 80% of all problems without any further investigation. However to the more experienced repairer this is only the first step as after you have "sorted" all the obvious problems you can then move onto, if required, the original fault knowing with more confidence that you are not firstly cutting corners and not going round in circles. Lastly I personally would not like to leave any suspect components just on the edge only to have to go back in a short time to repair the item again. sorry if this is very long winded!

[tom66]

Re: Bad caps often a symptom, not a cause

I had a 32" LCD TV (Hanspree) to repair. User reported it lost picture, then a couple of days later sound too.

I thought it sounded like bad caps (especially losing sound after a while.) This was further supported when I opened it up to find the PSU had some bulging caps (CapXon, of course) so my first step was to replace them ... no dice.

Later found a fuse on the inverter board was dud. And the user had accidentally muted the TV with no picture.

I've also got a Thomson Sky box which works absolutely fine, but has two bulging CapXons on the PSU board. I wonder how long it will last, parents won't let me fix it.