Very tricky capacitor replacement.

[davelectronic]

Not long picked up some old pc hardware, an hp usdt form factor desktop.
It runs fine, even with 4 x bulging electrolytic capacitors. So i know its worth trying a repair.
These capacitors are 6.3 volts 1000uf, but there legs are extremely close to traces of 1mm or less. I was thinking of a mechanical removal from above on the top side of the mobo, then remove each leg independently. I know the board has to be completely discharged of any residual power. But was thinking about cutting the capacitor body with absorbent material around its base, the cut through it and just leave the legs to remove.

This is a very tricky attempt, i would hazard a guess that its a one attempt scenario with regard to heating cycles to replace these capacitors.
Any thoughts appreciated, I've not got a microscope or a desolder station (although will get one soon) I'm really pushed for space at the moment,  and don't have a permanent workshop.
Any fail safe procedure considered. Some might say why bother, i really like the hp dc7700 usdt back in the day.
Thanks for reading.

[andy3055]

Not long picked up some old pc hardware, an hp usdt form factor desktop.
It runs fine, even with 4 x bulging electrolytic capacitors. So i know its worth trying a repair.
These capacitors are 6.3 volts 1000uf, but there legs are extremely close to traces of 1mm or less. I was thinking of a mechanical removal from above on the top side of the mobo, then remove each leg independently. I know the board has to be completely discharged of any residual power. But was thinking about cutting the capacitor body with absorbent material around its base, the cut through it and just leave the legs to remove.

This is a very tricky attempt, i would hazard a guess that its a one attempt scenario with regard to heating cycles to replace these capacitors.
Any thoughts appreciated, I've not got a microscope or a desolder station (although will get one soon) I'm really pushed for space at the moment,  and don't have a permanent workshop.
Any fail safe procedure considered. Some might say why bother, i really like the hp dc7700 usdt back in the day.
Thanks for reading.

Will this help?

[Shock]

If you are talking about through hole capacitors remove the motherboard and desolder them from the rear. Otherwise it might help to show which capacitors you are working on by attaching a clear image of the problem.

[m3vuv]

i did a similat thing on my ts-850,had a 16 pin dil to change without hot air etc,i used s dremel to grind/cut the legs then solder wick,luckily i didnt wreck any tracks,replaced it with a socket!,bit sort of brutal but it worked for me!,M3-VUV

[davelectronic]

Thanks for your replys. MR Carlsons lab, compressed air blast, bit risky in case a lump of solder ends up on neighbouring
Solder joints and i miss it.
Yes i will upload a shot in a bit of the offending components on the mobo. Worst compromise is using to much heat and messing up very fine traces.
Recently i did another capacitor replacement on a different board, had to use a lot of heat as it was on a substantial ground plane sucking the heat away from the the soldered leads. I got away with it, and it works fine. But i think motherboard capacitor replacement is probably one of the most challenging repair attempts.

[davelectronic]

So have a couple of images of the bad capacitors, they don't appear to be on a large ground plane. The capacitors with the black dots on top are the bad ones. And ringed the solder joints on the mobo under side. I don't know if you'd consider these tricky to remove, but one stuff up and its game over.
Looks like evidence of previous capacitor replacement, the yellow capacitor and two polymer capacitors

[davelectronic]

The under side showing the ringed solder joints.

[andy3055]

How about trying a vacuum de-soldering gun?

[mariush]

This is really not a problem to desolder.

The easiest would probably be to just put a big blob of solder between the two leads, basically short them with leaded solder (because it melts at lower temperature)
Then, simply put your iron tip on the blob of solder, hold it there until it's nice and liquid and start to wiggle the capacitor from the other side and then pull it out.

This way you may suck some solder into the holes, but it's not a big deal, it can be fixed with a stainless steel needle ... add blob of solder over the through hole, heat it well, insert stainless needle from other side to push solder out... solder won't stick to the needle.

Alternatively, you can get some pliers or something and just CUT the capacitor above the bottom rubber/plastic bottom. Then, remove the plastic bottom as well.
Turn the motherboard, again apply blob of solder between the soldered leads but when really liquid push the leads from the other side instead of pulling.

Don't be afraid to pump loads of heat into the board, there's copper layers inside the circuit board which will suck up the heat. It's not just copper traces on top and bottom. If you have adjustable temperature, set the iron to around 300-350 degrees Celsius, maybe even more.

The yellow capacitor I think it's also polymer, but in regular electrolytic capacitor case. I'm not 100% sure.

You can probably replace the electrolytic capacitors with 820uF 6.3v polymers (for the 1000uF ones)

And a bit unrelated but I saw a video above... a technique to remove soldered mounted capacitors

Jump to the video at 10:30


 

[TheMG]

they don't appear to be on a large ground plane

They most definitely are, you just can't see it because the ground and power planes are on internal layers of the PCB, which is pretty standard for PC motherboards.

You'll want a good high-wattage temperature regulated soldering iron. It may also help to pre-heat the board a bit to lessen how much heat your soldering iron has to dump into those planes. Adding a bit of lead solder to the joints may also help a bit.

Usually I heat up one pin of the capacitor and rock it sideways, then heat the other pin and rock it the other way, repeating the process until the capacitor is completely removed. Haven't had any luck with solder sucker or braid on these, the rocking technique has worked best I find.

[james_s]

Piece of cake, I did lots of capacitor replacements on motherboards back during the big capacitor plague.

I typically either cranked my soldering station up all the way and used a blob of solder to pass heat to the joint, or used one of those big Weller soldering guns. Heat up one leg at a time and rock the capacitor out. Make sure the solder is fully melted so you don't tear the plating out of the hole. You're overthinking this, it's really not hard.

[davelectronic]

Thanks for the replys. Ok so probably a ground plane, the last capacitor i replaced on a dell optiplex 745 usdt was a nightmare. I started that with 25 watt iron, i just couldn't get the heat in. I've got an Antex 25 watt and Antex 18 watt iron, but ended up using my Antex gascat 120. The amount of heat that can reach is scary  on such small solder joints. I have a couple of tips, a 3.5 chisel flat one side only, and a bigger 6mm chisel tip, i used that on the dell mobo capacitor. Even that took time to get the heat in, its a bit worrying having that much heat for more than a few tens of seconds. I've got an old motherboard, i think i will use it as a sacrificial practice board. When I've reached a decent level of proficiency,  i will go for it.
Thanks for the advice and links posted.

[wraper]

Thanks for the replys. Ok so probably a ground plane, the last capacitor i replaced on a dell optiplex 745 usdt was a nightmare. I started that with 25 watt iron, i just couldn't get the heat in. I've got an Antex 25 watt and Antex 18 watt iron, but ended up using my Antex gascat 120.

All of that are trash firesticks. Get yourself proper temperature regulated soldering station/iron. To make job easier preheat the board. If you don't have anything better, just steal a hair dryer from your wife and blow at area of interest for a few minutes at maximum temperature setting. Then do the soldering rapidly while board is still hot.

[Electro Detective]

FWIW I had a Gigabyte AMD pc board playing games on me     which had bloated electrolytic caps near the main processor,
a real pain to remove without screwing something up, and or napalming adjacent parts. 

Since I was in two minds about a PC upgrade anyway, and no one would see it, I just broke/trashed the dud caps away off the board (top side)
and blob soldered (with repeated attempts ) the new larger sized caps 'bent over' legs on to the old cap leg stubs,

then secured the caps as a group for support with electrical tape and cable ties,
betting myself it was never going to work and or the coldish crusty solder blobs would fail 

Hard to describe, but will admit it was THE most tacky slap up dodgy electroneek! job I've ever done
and strong contender for an EEVblog Repair Shame Award     if there is one.   


But the blobs held up, even though I expected to go back in eventually and sort it out, but never did,
it worked great till I upgraded to a pre-loved faster better PC some 3 years or so later.

i.e. electronics pride and aesthetics aside, one chooses to perform whatever works, what it's worth, 
and compare cost, time, convenience of a 'safely executed' hack job versus other proper repair/replace alternatives.

In my case, that day I needed that particular PC up and running again asap/yesterday
and back in the same spot with everything attached as it was, so I went the medieval route.. 

Would I do it that way in a heated rush job situation again? Probably yes since I got away with this one,
but would try and do a better tacky job of it 

[james_s]

25W is not nearly enough, 80W is probably the minimum I'd consider possibly adequate but more power would be better unless you have a way of preheating the board. A proper temperature controlled soldering station is the way to do it right, but I did have reasonable luck with a 140W soldering gun. Copper is a superb heat conductor, a big copper ground pour makes an excellent heatsink. You have to apply enough heat to the joint to melt it before the heat spreads out and cooks everything around it.

Your idea of clipping the capacitor bodies off is also valid, I've done that using some diagonal cutters on a few occasions and it can make it easier to get the pins out. The electrolyte is a paste so it doesn't just pour out all over.

[davelectronic]

I do have a hot air attachment for the gascat, no idea if that could be used for capacitor replacment. I'm definitely having a practice on an old mobo first, nearly purchased a desolder station a few days ago, but it was an unbranded Amazon special. Looked quite good though, and had reasonable reviews. When ever i buy any used IT stuff, open the hood and see bulging capacitors, my heart sinks. I should stop buying this old toot.

[james_s]

Funny, when I open the lid and see bulged capacitors I think "Ooh, cool! Easy fix!"

It's much nicer than poking around and finding no obvious explanation for the malfunction.

[jogri]

Funny, when I open the lid and see bulged capacitors I think "Ooh, cool! Easy fix!"

That feeling only lasts until you spot a leaking cap

In my experience those desoldering stations struggle quite a lot when it comes to pc mainboards, my 80W unit (a ZD-915) barely manages ground pins. The rocking technique works rather well up to four pins but takes a bit of time to get it out. But you should get yourself a better soldering iron, my suggestion for a good and semi-cheap (50 bucks) soldering iron would be the TS100 if you have a power supply with that plug.

[davelectronic]

Yes i will look into getting a soldering station asap. I've had an idea, bit unconventional, but maybe a viable option.
Drill a small hole in the top of capacitors, say 2mm - 3mm, use a very sharp pair of scissors or suitable cutters. Cut the capacitor can, remove it, remove the stack of dialectric material just leaving the capacitors leads. Trim and clean exposed leads, trim new capacitors leads, allow a clearance of a few millimetres, enough to solder new capacitor leads to old leads. Finish by applying a small amount of selastic or similar for mechanical support. I know it sounds crazy, but it leaves the original components solder joints untouched. Tell me that's a great idea and i will do it.

[mariush]

In some switching power supplies and high frequency voltage regulators, that extra bit of leads can add enough inductance and resistance to affect the operation.
For this reason, it's best to have the leads as short as possible, and for the same reason you will often find capacitors very close to heatsinks or parts that are hot (trying to keep loops as small as possible) when you would think there's enough room to position them a bit further away.

In your particular case, it would probably be fine, but I still think it would be worth using a quality soldering iron to desolder the leads properly.

[davelectronic]

Yes i do understand the need for short leads to deliver the charge and keep power clean. I will almost certainly use the conventional method.
Thanks for all the suggestions and help, much appreciated 

[jmelson]

I did a batch of these a couple years ago (not specific model, but similar mobo).  First, you might cut the old caps apart with wire cutters, I didn't, but it might make it easier.
Or, it might make it harder, depending on whether you can get the base of the cap apart, and then handle each lead separately.

So, get a good, high-power, temperature-controlled soldering iron.  My Weller WSL/WMP set is 65 W.  Heat one solder joint and apply leaded solder.  As this diffuses into the lead-free solder, it reduces the melting point.  Do both leads of one capacitor.  Then, heating one lead, push the cap body sideways to work the lead a little out of the board.  Move to the other lead, and work it out.  After a few cycles of this, the cap will come out of the board.

Now, the hard part.  You have to get the solder out of the holes.  I used one regular soldering iron and one vacuum desoldering tool with a hollow heating element.
I applied the rgular iron to one side and the desoldering tip to the other side, and vacuumed up as much solder as I could.  If the hole was not clear enough to put the new cap lead, I would fill the hole with leaded solder and repeat.  This would usually allow me to get the hole completely cleared.

If you are careful, you will not damage the fine traces on the board.  Be careful when clipping the leads of the new caps that you don't gouge the board.

Jon

[davelectronic]

Yes i do intend to get a soldering station soon. I would imagine clearing the holes completely of solder very difficult. Although a desolder station might work for complete solder removal. My experience of desolder pumps are not fantastic, I'm certain they would be of little use for mobo component replacement.
Well I've done it, and the pc is back together, replaced the old bios battery and it booted, complaining wbout the system time and date.

What i found was a steap angle with the soldering iron minimized possible contact with any of the super fine traces close to the capacitor leads. I thought I'd try the 25 wat Antex first, the csse iron is harder to manipulate on such tiny joints. It was just enough heat to do the job, dwell time was low enough. One glancing slide where i lost concentration for s second, but no damage done. I was thinking, I've got a second had supplier of these mobo boards should i need it lol. But that kind of defeats the bargain purchase factor.

This was the first mobo capacitor replacement for me, never done one before. My description of how it went, that would be quite stressful, and not as therapeutic as i would have liked. Your always aware that disaster is just a gouging slip away, waht worked for me was the rock back and forward method, ony after watching it to death on YouTube,  hoping some wizz youtuber would have a magic method, i did search, but nothing.
That was the pc with the most bad capacitors in it, i have another, but that only has two bad capacitors.
Below is the removed bad capacitors, other than some letters and numbers, they have no name on them. New replacements where same value and rating, and are Nichicon capacitors.
So far so good, pc still working...
Thanks again for all your replys comments and help. 

[jogri]

Below is the removed bad capacitors, other than some letters and numbers, they have no name on them.

They might not have the name of the manufacturer printed on them, but you can identify them by that "fancy rectangle". That is the logo of Chemi-Con; in your case those were manufactured by the US department of Chemi-Con: http://www.paullinebarger.net/DS/Chemi-con/UCC%20%5Bradial%20thru-hole%5D%20KZG%20series.pdf

[mariush]

United Chemi-Con / Nippon Chemi-Con / whatever it's called in general makes very good capacitors.

The KZG is just one of their series that was faulty, had a somewhat unstable formula and some motherboards had capacitors from this series that went bad without ever powering the board, just sitting on shelves.
It's an ultra low esr series, and other manufacturers of capacitors also had "ultra low esr" series that went bad more often than others.