Bad Capacitor?

[Darshevo]

In an effort to make some room in my work area I am wrapping up some of the project I have let lie too long.

This one is the power supply board from an LCD I picked up at the recyclers.

My question is 2 fold. In the picture below the caps in the center have a bulged out top, where the ones on both sides are flat, or maybe even a little convex. Safe to assume they have gone south?

My second question is this, if they are indeed bad, isn't safe to assume something caused them to fail? In which case I should be looking for a deeper issue lest I find myself replacing them immediately after installing the new ones

Sorry to have so many questions, but I am pretty green in electronics. I've read 2 different books on the matter, but have probably learned more here in the last few weeks applying what I have learned both from the responses to my posts as well as the projects of others (both on the forum and in their worklogs/blogs) than I've learned in a year of dabbling and reading.

-Lance

 

[tezza]

My second question is this, if they are indeed bad, isn't safe to assume something caused them to fail? In which case I should be looking for a deeper issue lest I find myself replacing them immediately after installing the new ones

Lance, my understanding is that it's not necessarily an underlying cause. Some caps just go this way after a while.

Those look like they are bulging to me so I'd certainly replace them.

Terry

 

[Vlad]

Safe to assume they have gone south?

Beyond a doubt, they should never be anything but flat.

My second question is this, if they are indeed bad, isn't safe to assume something caused them to fail?

Not necessarily. That can happen with age, bad electrolyte, a lot of things. Happens to older motherboards a lot. That doesn't mean something else hasn't gone bad too though but generally it happens because they were poorly manufactured.

 

[Ole Juul]

The caps in the middle are also snuggled in between those two heat radiating heat sinks. Perhaps they have been a little warmer during operation thus making them fail earlier.

 

[cosam]

Perhaps they have been a little warmer during operation thus making them fail earlier.

That's probably it - the hotter they run, the shorter their lifetime. It's worth looking for a high temperature rating in a replacement part. You should be able to find aluminium electrolytics rated for 105 degrees, maybe even 125.

I don't think CapXon are renowned for quality either. For the few pennies difference it makes, it's worth sticking to well-known brands.

 

[NeXT]

I don't think CapXon are renowned for quality either

In the badcaps.net community, capXon is well known as being a bad brand. Just replace all similar branded caps on the board with caps of similar rating and you should be fine.

 

[Dr_V]

When replacing capacitors on a PSU you can safely use new ones that are of slightly bigger capacity (about 10 to 20% bigger). Many PSU manufacturers usually mount the smallest possible capacitor and often they underestimate the value.

The most common cause for PSU capacitors failure is a bad electric grid (power fluctuations) plus a large consumer on the output side of that PSU.
The real load on any PSU must always be kept under 80%. If you can't do that make sure you replace all capacitors with bigger ones.

 

[channelmaniac]

Luckily you don't need anything drastic for this power supply like "Low ESR" type caps... Just standard aluminum electrolytic capacitors.

You can find many different ones out at mouser.com - I'd personally go with Nichicon in a 105 degree rating. Those were the caps we used when I worked at a grey market repair center fixing old Macintosh systems.

 

[Old Thrashbarg]

That's probably it - the hotter they run, the shorter their lifetime.

Not in the case of CapXon and many of the other cheapo Chinese brands. They will fail after a couple years, invariably, even under ideal conditions. It's due to the cheap, inferior electrolyte formula used. It's a common problem, especially on parts from around 2000-2004.

It's possible something else got fried when the caps went, but most of the time, it's just the caps that are bad. I've repaired dozens of motherboards and PSUs with such issues, and it's generally been a pretty simple matter to get things working again once the capacitors are replaced with good ones.

I'd be a little wary of Nichicon, though. They're probably OK if you get them from a known trustworthy supplier, but there are a lot of fakes out there. I generally use Panasonic, Xicon or United Chemi-Con just to be safe, since I've never seen counterfeits of those.

 

[Chuck(G)]

CapXon and "RulyCon" are the two most-replaced brands in my shop--I've seen them most often in LCD displays, but routers also figure high on the list. With LCDs, one common complaint is that the display just comes on for a few seconds and then powers down or recycles. With routers, the power light comes on and maybe some of the activity lights, but otherwise the thing appears to be bricked.

As replacements, I like Panasonic, Elna, CDE, Sprague and Nichicon. Beware of Chinese fakes, however...

 

[Darshevo]

Thanks for all the excellent replies. I desoldered the suspect caps last night and am going to see if I can find a local supplyhouse that has them. I haven't ever seen anyone other than RS locally, but I got a couple good references last night off google. If it comes down to 'the shack' I'll probably back burner this for a few days and order the parts off line.

CapXon and "RulyCon" are the two most-replaced brands in my shop--I've seen them most often in LCD displays, but routers also figure high on the list. With LCDs, one common complaint is that the display just comes on for a few seconds and then powers down or recycles.

That was just about the problem with this lcd was that it has a flickering red led where there should apparantly be either a green (I;m happy, working, and on) or a yellow (sleeping)

On a side note, I checked out the resistors with my ohmmeter while I have it apart. To make sure I am reading it correctly with the meter set to 2k a 330ohm resistor reads .326 (with the +/- accounting for tolerance). That would make a 1K resistor about 1.0 and a 2k 2.0? I know I have at least 1 bad one as 1 of the 2k resistors measures 1.832 while the other is .956. They are both 5%, so the first one isn't way out of line, but the second seems pretty low. With my limited experience I have never seen one that was bad that wasn't easily recognizable due to being visibly burned.

This is going to be a fun little project - it will be good to stretch my mental legs a little bit

-Lance

 

[channelmaniac]

Not necessarily.

When reading parts in circuit you will be reading the resistance through them AND through other paths.

The only way to truly read the part is to desolder it.

Resistors don't usually change values like that when bad. They tend to be a working or not working part. Yes, it can happen, but is very uncommon.

As for fake parts, buy from reputable sources. That's why I suggested mouser.com

RJ