Why did the capacitor from my power supply blow up?

Thread Starter

Engibeer28

Joined May 4, 2018
7
A capacitor of my power supply that powers my monitor blew up yesterday. I was just studying at my PC and it suddenly poped. What exactly happened here and why?
Thanks in advance for any helpIMG_20190128_213908.jpg IMG_20190129_005029.jpg IMG_20190129_011305.jpg IMG_20190129_005007.jpg
 

Yaakov

Joined Jan 27, 2019
1,612
The cap saw too much current, heated up, and the pressure blew the can off the seal on the bottom.

Why? Some upstream component(s) failed. Those caps seem to be part of the filter but the layout of that supply seems odd.

It is possible that age and heat damaged something (the transformer?) and let the caps see an over voltage.

The bottom line is, get a new supply. 12V@3A isn’t very special, you should be able to find one.
 

wayneh

Joined Sep 9, 2010
16,400
I agree that you can find a cheap or free replacement - check the recycle dump. But replacing the caps wouldn't cost much and might fix it, if that approach appeals to you. Just be sure to use replacements with temperature and ESR ratings at least as good as the old ones.
 

Yaakov

Joined Jan 27, 2019
1,612
I agree that you can find a cheap or free replacement - check the recycle dump. But replacing the caps wouldn't cost much and might fix it, if that approach appeals to you. Just be sure to use replacements with temperature and ESR ratings at least as good as the old ones.
Before doing that, it would make sense to check the voltage at the caps and be sure there isn’t a dangerous voltage there.

If the transformer shorted, there could be mains at the caps.

Safety first.
 

MrChips

Joined Oct 2, 2009
22,089
Looks like a SMPS and the capacitors are on the low voltage side.
Check the voltage rating of both capacitors and go with higher voltage, i.e. 25V instead of 16V.
 

Thread Starter

Engibeer28

Joined May 4, 2018
7
Thank you for your answers. The capacitor probably failed, it is a 7 years old power supply. I will now check the voltage of the capacitors and try to replace the faulty one and if I find trouble doing this I will just buy a new PSU.
 

kubeek

Joined Sep 20, 2005
5,733
Looking at how cheaply that power supply is made - lots of unpopulated places for components that should be there, but were decided unnecessary to keep the price down - it might be a better idea to look for a new one.
 

recklessrog

Joined May 23, 2013
985
Check the resistor in front of Q2 the transistor on the heat sink. Photo is not too clear, is it R5 or R6? it looks like some of the coating has blown off, it may well be open circuit caused by shorted switching semiconductors.
 

Kjeldgaard

Joined Apr 7, 2016
424
Thank you for your answers. The capacitor probably failed, it is a 7 years old power supply. I will now check the voltage of the capacitors and try to replace the faulty one and if I find trouble doing this I will just buy a new PSU.
The left, of the large electrolyte capacitors, on the first picture also looks sick (Raised top and visible rubber gasket at the bottom).
 

AlbertHall

Joined Jun 4, 2014
10,554
Thank you for your answers. The capacitor probably failed, it is a 7 years old power supply. I will now check the voltage of the capacitors and try to replace the faulty one and if I find trouble doing this I will just buy a new PSU.
If you go for repair, I would replace both capacitors. They've both had the same life - time, temperature, voltage...
 

MrChips

Joined Oct 2, 2009
22,089
The other capacitor will not likely pop. It has already released its pressure by pushing out the bottom plug. It's as good as dead. Replace both capacitors with higher voltage ratings.
 

BobaMosfet

Joined Jul 1, 2009
1,224
A capacitor of my power supply that powers my monitor blew up yesterday. I was just studying at my PC and it suddenly poped. What exactly happened here and why?
Thanks in advance for any helpView attachment 168921 View attachment 168920 View attachment 168923 View attachment 168924
1. it was weak. 2. it was defective. 3. it was a knock-off part (rampant in the capacitor industry) 4. something else failed, and took the cap with it. I'm sure other possibles exist.

As it's an electrolytic, it's easy to replace- slap another like one in and see if the unit operates.
 

ian field

Joined Oct 27, 2012
6,539
A capacitor of my power supply that powers my monitor blew up yesterday. I was just studying at my PC and it suddenly poped. What exactly happened here and why?
Thanks in advance for any helpView attachment 168921 View attachment 168920 View attachment 168923 View attachment 168924
Most likely loss of electrolyte resulting in high ESR. That resistance dissipates/wastes heat when ripple current is flowing..

dodgy electrolytics in SMPSUs can build up a head of steam sufficient to burst violently.

The creases you can see on the tops are to deliberately weaken the can so it vents safely. This was known about since (practically a battery) totally liquid electrolytics were superceded by foil types - there was a steady stream of technicians blinded by high velocity capacitor cans. Don't buy the same brand that didn't fail safely!!!!!

You can't use just any old electrolytics - they have to be special low ESR types.

Its also possible they were over volted by regulation failure. A small capacitor that stores a voltage sample for the regulation section is often the cause, it can also be the resistor divider that sample comes from.

It probably isn't a difficult repair as long as nothing went bang on the primary side, check the secondary side rectifiers (Shottky barrier diodes looking slightly leaky is normal - but not acceptable on fast silicon types). If there's an opto coupler isolating the feedback loop - I'd just replace it because that's easier than the PITA procedure to test it properly. the opto must have a VDU qualification.
 

Thread Starter

Engibeer28

Joined May 4, 2018
7
When I decided to replace both capacitors I noticed that the R11 resistor was blown up too and left a black mark on the board. Do you think that this made the capacitor blow up in the first place?
I think I should just buy a new PSU. IMG_20190202_134617.jpg IMG_20190202_134723.jpg
 

AlbertHall

Joined Jun 4, 2014
10,554
I doubt it is the cause of the problem, more likely another symptom.
It probably makes sense to buy a new one unless prohibitively expensive.
 

Tonyr1084

Joined Sep 24, 2015
5,232
In the US I just go to the nearest Xfinity store and ask if they have any returned equipment and are willing to part with a few 12 volt supplies. They typically are 3 amp devices.

I've opened a few of those things and have found over the years that some of them have ratings they've overstated. Things like "3000 mA" when they are more likely capable of sustaining 2000 mA or even less. Since I know a quick, ready and free source I just go there periodically.

Craig's List is another good hunting ground. I get quite a few used and unwanted printers that come with power supplies. I have one open on my bench right now that pushes 18 volts at 5 amps. I've been thinking of resetting the reference voltage so that it outputs 14 volts for use on things like automotive equipment; or to keep batteries charged. Certainly don't need 5 amps, but it's there. And was free.
 

spinnaker

Joined Oct 29, 2009
7,835
In the US I just go to the nearest Xfinity store and ask if they have any returned equipment and are willing to part with a few 12 volt supplies. They typically are 3 amp devices.

.

Never thought of that. But then again, I have enough wallwarts to last me several life times of projects. ;)
 

davidgreams

Joined Feb 2, 2019
3
It happens, if the seal at the bottom is weaker than the score marks at the top. Solder new ones in and the supply should be good for another 10 years. Caps are the only thing that regularly goes bad in these things.
 
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