Is this capacitor failing

Thread Starter

Avi08

Joined Dec 29, 2021
4
This is the cap(the one on the left) on the power board of my monitor. 4700uf 25V. Since the monitor turns off in a few seconds everytime I power it up I tried to take a look. Since it is not egregiously bloating I was wondering when do caps like these stop working or is it already a goner?IMG_20211229_184906__01.jpg
 

MrChips

Joined Oct 2, 2009
30,806
The X on the top of the can of an electrolytic capacitor is put there intentionally in manufacturing.

When electrolytic capacitors are abused the electrolyte vaporizes and pressure builds up in the can.
The X on the top is a weak spot that allows the can to open up and release the built-up pressure. Otherwise the can will explode in a very dramatic way. Usually a crack appears at the center of the X and brown material starts to appear at that vent (very much like a volcano prior to full eruption).

1640786653991.png


Any electrolytic capacitor that shows evidence of bulging or leaking at the top or base is suspect and should be replaced.
 

MisterBill2

Joined Jan 23, 2018
18,502
The X on the top of the can of an electrolytic capacitor is put there intentionally in manufacturing.

When electrolytic capacitors are abused the electrolyte vaporizes and pressure builds up in the can.
The X on the top is a weak spot that allows the can to open up and release the built-up pressure. Otherwise the can will explode in a very dramatic way. Usually a crack appears at the center of the X and brown material starts to appear at that vent (very much like a volcano prior to full eruption).

View attachment 256323


Any electrolytic capacitor that shows evidence of bulging or leaking at the top or base is suspect and should be replaced.
Actually, any electrolytic capacitor that shows evidence of bulging or leaking at the top or base has failed and should be replaced. Of course they may only be slightly failed, a bit like only being "slightly dead." AND, they can also fail by losing capacitance without any bulging on top.
 

dl324

Joined Mar 30, 2015
16,918
Since the monitor turns off in a few seconds everytime I power it up I tried to take a look. Since it is not egregiously bloating I was wondering when do caps like these stop working or is it already a goner?
The cap is going bad. Since the monitor is turning off, you should just replace it. It's an easy job on a single sided board.
 

MrChips

Joined Oct 2, 2009
30,806
The cap is going bad. Since the monitor is turning off, you should just replace it. It's an easy job on a single sided board.
And a very difficult job on a multi layered board.

I would suggest that you cut away the can of the capacitor while leaving the capacitor legs intact.
It would be easier to solder the legs of the replacement capacitor directly to the legs remaining in the holes.

You can also attempt to remove the legs from holes by applying heat to both sides of the board.
Also cleaning the holes to accommodate the replacement capacitor is not easy. I use steel pins to open up the holes.

It is not uncommon for the POWER and GND planes to be placed on inner PCB layers which makes the repair very difficult.
 

MisterBill2

Joined Jan 23, 2018
18,502
If the capacitor is pulled off, then the stub can be grabbed with pliers on the component side and heated with a decent iron on the other side and it should pull right out. But the soldering iron must be clean enough to supply enough heat to melt the solder all the way through the hole, if it is a plated through hole. That generally means a 30 watt iron. Also, the pliers should not be all the way down to the board surface, because they act like a heat sink and keep the last bit of solder too cool. Don't pull until the solder is completely melted.
 

dl324

Joined Mar 30, 2015
16,918
@Avi08
To clarify. Your board is single sided and you won't have any problems with ground planes or plated through holes. If you can solder at all, the cap won't be difficult to remove.

If you can't solder, ask for pointers.

BTW, welcome to AAC!
 

Thread Starter

Avi08

Joined Dec 29, 2021
4
@Avi08
To clarify. Your board is single sided and you won't have any problems with ground planes or plated through holes. If you can solder at all, the cap won't be difficult to remove.

If you can't solder, ask for pointers.

BTW, welcome to AAC!
Haven't done much of soldering but I guess we all start somewhere.
Thank you! Glad to be a part of the community.
 

dl324

Joined Mar 30, 2015
16,918
Haven't done much of soldering but I guess we all start somewhere.
I'd advise you to practice on something that isn't important.

What is the wattage/temperature and tip style of your soldering iron?

If you intend to use solder wick to remove the solder, you can pull off pads/traces if the solder cools too much before you remove the braid. If you use a solder sucker, you can suck up pads and traces if you get them too hot (the adhesive melts).

This is more of a problem on single sided boards. On boards with 2 or more layers, plated through holes will hold the pads down when the adhesive gets soft, but you can still lift them.

Post a picture of the solder side of the board so we can see the traces for the cap you need to remove.

Thank you! Glad to be a part of the community.
It's traditional for the member who has the honor of replying to a new member's first post to welcome them.
 

panic mode

Joined Oct 10, 2011
2,749
i strongly agree. get any old PCB with similar type of components and practice desoldering. practice makes perfect. common problem is overheating and damaging PCB or components. using braid requires less practice than using solderpump. also with braid there is no kickback at the most important moment (solid grip here can be very important).

the good news is that your PCB is single sided ( all copper traces are at the bottom of the PCB). this means holes are not plated through and there are no other layers to act as a heatsink. if you don't know what i mean, try desoldering things from some old motherboard and you will see how much more heat is needed. and while without plated through holes, traces peel easier... upside is that repair is easier too since everything is in plain sight.
and i would replace ALL of aluminum can caps at once regardless if they show bulge./leak or not. caps are cheap and this is common maintenance issue so better do it right and get new caps in.
 

Thread Starter

Avi08

Joined Dec 29, 2021
4
I'd advise you to practice on something that isn't important.

What is the wattage/temperature and tip style of your soldering iron?

If you intend to use solder wick to remove the solder, you can pull off pads/traces if the solder cools too much before you remove the braid. If you use a solder sucker, you can suck up pads and traces if you get them too hot (the adhesive melts).

This is more of a problem on single sided boards. On boards with 2 or more layers, plated through holes will hold the pads down when the adhesive gets soft, but you can still lift them.

Post a picture of the solder side of the board so we can see the traces for the cap you need to remove.

It's traditional for the member who has the honor of replying to a new member's first post to welcome them.
Thanks for the advice. My iron is 40w. It's a quite simple one.IMG_20211231_154032__01__01.jpgIMG_20211231_152739__01.jpg
 

MisterBill2

Joined Jan 23, 2018
18,502
That soldering iron could work, although using a broader pointed tip will make the job go faster. And 40 watts will be plenty of heat. But the tip needs to be shiny and you will probably need to add a bit of solder to provide adequate heat conduction onto the existing solder . Also. it will help to straighten the wires before trying to pull out the failed capacitor. You will need to do one lead at a time, gently pushing the capacitor sideways so a to pull out the lead with the melted solder, and then the opposite direction as you heat the other lead. The process is tedious but not difficult. And it will take several times back and forth to get the capacitor out, so patience is mandatory.
 
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dl324

Joined Mar 30, 2015
16,918
My iron is 40w. It's a quite simple one.
Do you know what temperature it can reach? You want to be able to get to 700-800F for rework.

As has been mentioned, the tip has a lot of oxidation on it. You can try using solder with a flux core to remove it. If that doesn't work after using several inches of solder wire, you can scrape it very gently with a blade. Whatever you do, you don't want to scratch/gouge the coating.
 

MisterBill2

Joined Jan 23, 2018
18,502
For unsoldering it takes more heat. and it takes having some melted solder to conduct heat onto the joint being unsoldered. That is where the older texts are all wrong, They imply just a point of contact is adequate. It is not adequate. And by the way, it is very possible to do a quite good job of soldering with a much cheaper, non-temperature controlled, soldering pencil. It does require focussed attention and knowing exactly what to do and when to do it.
 

Thread Starter

Avi08

Joined Dec 29, 2021
4
Do you know what temperature it can reach? You want to be able to get to 700-800F for rework.

As has been mentioned, the tip has a lot of oxidation on it. You can try using solder with a flux core to remove it. If that doesn't work after using several inches of solder wire, you can scrape it very gently with a blade. Whatever you do, you don't want to scratch/gouge the coating.
No. The product specifications just mention auto temperature.

Okay. Seems like I was taking this job lightly. Will definitely practice adequately on junk boards before attempting on this one.
 
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