built to die or bad design?

[souNdguy]

buddy called me at lunch, his lcd monitor died for his desktop computer. turns on for a second, then pops off.

I 'guessed' wildly that it might be a bad cap int he power supply.

he goes online and finds a user group and there were multiple issues of that brand/model monitor doing that. seems 1-5 capacitors ( out of the 6 ) on the power supply daughterboard tend to die prematurely. (2) 1000u / 25v and (3) 220u / 25v. ( rs units were same u but 35v rated.. etc.. no biggie for ps issues.. )

He poped the chassie apart at lunch while I was on my way over.. sure enough.. blown rubbers onthe bottom and dimpled tops on 5 of the 6 caps.

radio shack amazingly had the right value caps in stock, and they were nearly exactly the same size. board was double sides with plenty of surface mount stuff so I took my time to desolder and pul and replace the bad caps.

surgery went well, monitor came right back to life as soon as we pugged it in, despite the fact that a lil 1/4w resistor near one of the caps got hot enough to flake it's enamil off.

now.. here's the deal.. here's why i think bad design. 5 of the 6 caps are situated within 1/8 to 1/4 inch of an aluminum heat sink with the rectifiers and vreg chips sunk to it..

IMHO.. the het sink is radiating too much ir off and cooking the caps.

monitor is less than 2ys old.. they really should last longer.. IMHO.. poor circuit board layout.

I notice it is a daughter board.. I bet they repalce alot of them for warranty service due to this..

oh well.. 3.58$ saved this one.. for now..

soundguy

 

[William Fissell]

good job!

maybe the same compnay manufacturs them as makes CNH's voltage regulators!

 

[souNdguy]

naa.. this monitor worked for a while.. it wasn't DOA out of the box


soundguy

 

[raycole]

My understanding is there was a company that produced a bunch of capacitors a few years back that were manufactured improperly. I have heard 2 stories. One story claims that the founder of the company thought he stole the process from another company he worked for, but what he stole didn't include a vital step. He was able to sell them cheaper than the competition so more got used. Another story claims it was just a quality control breakdown. These capacitors have been used in numerous applications, and for computer motherboards that are a few years old or so the usual cause of failure is from one of these bad capacitors. I found a bad set in a small router recently. Not surprisingly they look an awful lot like the capacitors that went out on a motherboard I had... Whatever the reason, there do appear to be a lot of bad capacitors floating around. My understanding is the issue has been resolved so 'newer' stuff shouldn't have the problem. But...no telling how long it takes some items to get used up that had these bad capacitors.

 

[Teakettle]

If you're going to go to all the trouble of replacing blown aluminum electrolytic caps in a piece of electronics that you expect to keep awhile, it's usually worth the extra money to replace them with tantalum caps.

 

[John Smith8N]

Had a similar problem with my Viewsonic monitor, it made it just past the 2 year warranty period. Found the info online about the capacitors. Opened it up and sure enough, 4 bloated electrolytic caps. Replaced them with almost right ones from Radio Shack and it has worked ok another year now. Seems to be a common problem.

 

[souNdguy]

could be.

I've seen electrolytics pop and dry out before.. but these got hot and .. well.. really hot. there is a plastic shell on the back of the monitor.. 2 of the caps burned 'cigarette' sized marks into the plastic. Wouldn't surprise me a bit if it was a marginal component as 6 of the5 died.. and those 5 were closer to a heat source than the other.

soundguy

 

[souNdguy]

unfortunately.. I don't like to buy in lots of 10 or more.. or pay 9$ shipping on a 35 cent item.. so i made due with radio shack electrolytics that were down the street I could purchase locally... should be fine.

soundguy

 

[souNdguy]

hmm.. this seems to be a pretty common issue then.. different brands too.

must be one common supplier a while back that sold a bunch of marginal caps to a bunch of manufacturers.

Wish I could have read the color codes on that resistor that near burned up .. i'd have replaced it too.. but it's enamil darkened and near burnt off leaving it unidentifiable.. oh well.. the monitor works.. for now.. and was a cheap fix. if he gets another 6mo out of it it will be a good gamble.

soundguy

 

[JMOR]

(quoted from post at 15:36:05 05/13/10) Had a similar problem with my Viewsonic monitor, it made it just past the 2 year warranty period. Found the info online about the capacitors. Opened it up and sure enough, 4 bloated electrolytic caps. Replaced them with almost right ones from Radio Shack and it has worked ok another year now. Seems to be a common problem.

Geo Tracker ECM. Capacitor fixed it. Saved a lot more than cost of typ 'puter monitor. See burnt/leak area, magnified inset, upper left.

 

[Dean]

In a former life I once designed switching regulators for computer equipment. In order to minimize space requirements and cost, most filter capacitors are worked quite hard.

If one gives the capacitor internal impedance short shrift, the capacitor(s) will overheat resulting in a shortened life or worse.

Dean

 

[souNdguy]

yep.. don't take much. the pc board on this daughterboard looke dmucht he same way around that capicitor cluster.

soundguy

 

[souNdguy]

sounds like what happened here. 2 sets of the caps ( 4) were in 2 sets of parallel. IE.. the 2 1000u were paralleled, and 2 of the 3 220u were paralleled.. and all close tot he heat sink. my guess is one or 2 became marginal and died causing a cascade failure of the others...

I bet it saved them a penny per board to underdesign it that way..

soundguy

 

[Bob]

It's called "capacitor plague".

Here's a link to some HEAVY reading about it...
Sick, sick caps

 

[souNdguy]

good article.

soundguy

 

[36 Coupe]

This is an old problem,Ive had caps squirting fluid at me in late model fence chargers.Much crap is being sold now.

 

[souNdguy]

according to that article I read.. as late as 2007 they were still being sold out to manufactureres. figures..

soundguy

 

[Stephen Atkins]

Lowest bidder??

steve

 

[souNdguy]

can't imagine why not


soundguy