Hello,
I've got a couple of Intel boards (D865PERL) that have one bad electrolytic capacitor each. One board stopped working; the other still works, but has a bulging cap close to the CPU area. (Pics not yet available.)
Is desoldering these caps straightforward? Any special precautions re: multi-layered PCB traces? Any special gotchas to keep in mind when ordering replacement caps from say Mouser?
Thanks,
Michael
I fully recapped a pair of Dell Optoplex GX-280 mother boards. About 15 or so caps per board.
Using a vacuum desoldering tool is the best method, but you can remove the caps but using a wide enough tip to hit both leads at the same time, then go back and clean the solder out of the holes with a piece of stainless steel like a dental pick. Melt, stuff, let cool and remove.
On the caps look for "low esr" and 105C temperature range. I try to buy Nichicon caps by default. At $1 or so apiece, it's not worth saving a few cents to get a crap cap that won't last.
Jeff
If you can clamp to the cap and pull at the same time it helps, I use a surgical instrument like arterial forceps but longer opening arms and full gripping teeth (retraction clamp?). For the cleaning out of holes I made up a set of needle probes from different sized st/st sewing needles glued into ballpoint pen barrels or into drilled dowel
No 16 of part of my tool kit is the specific clamp
goggling , probably Baby-Allis forceps
My experience is that if you have the usual 8-10 identical capacitors on the motherboard, and one is visibly defective, then the others are highly likely to fail very soon. I replace *ALL* the caps of a specific type. In particular, the caps around the CPU tend to die, because of the heat and the high ripple current. Typically, I'll replace 10 to 15 caps.
It varies. Some boards are very easy to unsolder. Others have smaller holes for the leaded parts and are more difficult. A vacuum desoldering station is best. Use plenty of heat and some liquid flux so that you don't pull the plated thru hole out with the capacitor. If you see a copper colored ring around a capacitor lead, you've probably killed the board.
If you don't have a tip that will heat both leads at the same time, or don't have 3 arms so that you can use two soldering irons, all is not lost. I heat up one lead, and rock the capacitor in the opposite direction. After it moves a little, I heat the other lead, and rock it in the opposite direction. Don't use brute force or you'll rip out the plated through holes. Eventually, it comes out.
One lead is usually grounded where the large copper area acts as an effective heat sink. This lead will be more difficult to unsolder than the hot lead (usually +). I use a big, wide (1/4"), hot (850C), chisel tip. Plenty of heat, and work fast. This will take some practice. Find an old PCB and practice a little before attacking the Intel motherboard.
105C Low-ESR. Watch the case dimensions and lead spacing. If it will fit, try to buy the next higher voltage rating. I'm partial to Panasonic but will use Rubycon. Digikey, Mouser, and eBay (in that order). I sometimes use polymer caps as replacements, when the motherboard is worth fixing and the customer doesn't care about the cost. Also, think about buying an ESR tester if you're going to make a habit of this.-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
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Ok, thanks to everyone who replied. Seems doable... looks like I'm going shopping for a vacuum desolderer.
Michael
For a one-off project, desoldering braid (it sucks up solder like a sponge) is almost as good, and doesn't have the sticker-shock effect.
Practice on a scrap board or two FIRST. It's easy to damage things while the iron is hot and the polymers are soft.
I've done this on motherboards; it's tedious, but practical. The suggestions from others are good. Here's a few things I discovered.
While vacuum desoldering tools work well, you have to heat the board to the point where the solder on the ground lead melts all the way through the board. The vacuum desoldering tools aren't real efficient at transfereing heat unless you add a little solder or flux to each lead you are going to unsolder.
The technique I settled on was to use a 40 watt soldering iron with a chisel tip. Heat up one leg, add a dab of Chip-Quik, rock the cap toward the opposite side. Heat up the other leg, add Chip-Quik, rock cap to other side. Repeat with the heating and rocking until the cap drops out. While it's still hot, push an iron or stanless steel needle through the hole (I use a dissecting pick I got in the '60's). Remove the pick when the solder has cooled; reheat the other hole and use the needle.
Make sure you keep a chart identifying which cap goes where. Patience is necessary. Make sure you clean up all stray solder.
PlainBill
Good advise and also make sure you take note of the polarity.
While a proper vacuum desoldering station is nice, you can get away with using a solder sucker.
It requires some practice at both using and cleaning. I use one when I'm too lazy to fire up the desoldering station.
Someone suggested using solder braid. I disagree. I've lifted so many traces and pads from the board with solder braid, that I won't use it unless I'm depserate.
Don't forget the stainless steel needle or pin for cleaning the hole.
-- # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060 # 831-336-2558 # http://802.11junk.com jeffl@cruzio.com # http://www.LearnByDestroying.com AE6KS
About the only thing solder braid is good for is phenolic PC boards with brass rivets for the through holes.
That and lifting traces.
Jeff (the other other one)
And cleaning the solder off the pins of Octal tubes. :(
-- Politicians should only get paid if the budget is balanced, and there is enough left over to pay them.
I recently restored and fully recapped two Kenwood KA-9100 amps. All the boards are phenolic and I used solder braid on them. Surprisingly they held very good, not a single lifted trace. I do have all the usual soldering stuff--hot air, vacuum desoldering station etc.--but braid was the best one for the job. It even allowed me to remove all the switches and pots for cleaning (I disassemble all of them and clean all the contacts with silver cleaner occasionally replating some with new silver coat and replating severely oxidized hardware with new yellow zinc coat.) It is not an easy task to do on modern boards because some of those switches have too many pins... Kudos to Kenwood for using such a good material for their boards...
BTW I do remove all those wire-wrap studs, drill bigger holes, and install turrets instead. Eyelets installed in those holes where interconnection wires go.
Those KA-9100 BTW look very very good for their 30+ years age. All solder joints look like they just came from the factory. If not that horrible design flaw in phono preamp section that makes them fail I would say it is an engineering gem and an example how such things should be manufactured.
-- ****************************************************************** * KSI@home KOI8 Net < > The impossible we do immediately. * * Las Vegas NV, USA < > Miracles require 24-hour notice. * ******************************************************************
t e
Yes... I was having visions of getting the cap out then wondering, which way is negative... :-D
Thanks y'all
Michael
And they are not multi layer boards with 0.010" traces.
Jeff
They are not. There is no such thing as _phenolic_ multi layer boards with
0.010" traces.BTW, solder braid is very useful on _ANY_ board, including multilayer ones with 0.010" traces. It requires some skills of course but everything does. I do use it all the time.
It is not the rifle that shoots way off the target, it is the shooter.
-- ****************************************************************** * KSI@home KOI8 Net < > The impossible we do immediately. * * Las Vegas NV, USA < > Miracles require 24-hour notice. * ******************************************************************
Usually there's a circle printed on the board under each electrolytic capacitor, and the negative side is filled in, but Asus and Asrock boards are marked the opposite way, so the filled area indicates the positive lead instead.
There are YouTube videos about soldering and desoldering, and BadCaps.net has a lot of information and also sells high-quality caps. I think they also have a YouTube video.
In my novice opinion, a mainboard made with leaded solder needs a 40W iron to solder it, a 50W iron to desolder it, and lead-free boards need even more power. But a regular 50W iron can overheat its tip and turn it blue or oxidize it, which really hurts heat conduction. There are adjustable power irons for as little as $10, but I've found that cheap irons don't last long or don't deliver as much heat to the tip as good irons of the same power rating. BTW if you buy one off Ebay, check the voltage because many are made only for 220VAC. If you're going to spend much at all on an iron, consider getting a temperature- controlled, 70W Goot PX-201, about $50, which should be able to handle about anything, and Goot is a quality brand. Temperature-controlled is better than adjustable power. With any iron, a chisel tip, about
2mm - 2.5mm wide, works better than a conical tip, and tips are best cleaned with curly brass hair or a damp paper towel, not a sponge.Manual desoldering vacuums work best if you can hold them on one side of the board and the iron on the other side and see both sides at once. Vacuum bulbs don't suck nearly as well as spring plungers do, but the latter can strike and damage board at the moment the spring is released. Addng a short length of rubber tubing can prevent the damage.
Copper desoldering braid works if it's the right width (enough to soak up all the solder from the hole in one try but not more, generally
2-3mm and the iron puts out plenty of heat. Cut off the used portion immediately after use so it won't absorb heat from the next joint. Don't pull out a lead unless all of the solder from the hole has been removed, and test by wiggling the lead side to side. Generally if all the solder doesn't come out in one try, it's best to fill the hole with 60/40 or 63/37 solder and start all over.Chip Quik may be the easiest and safest way to desolder because it melts at under 150F, but it costs about $1 per inch.
Radio Shack sells an $11 desoldering iron with a vacuum bulb, and other sources have a similar tool that has a spring-loaded plunger vacuum instead. The Radio Shack iron doesn't seem to deliver quite enough heat to the tip for multilayer boards, but people have modified it with a better vacuum pump or by wrapping heat insulation above the tip.
Not yet. Some experiments in printed semiconductors and 3D circuits use multilayer boards. However they don't use solder. They're stapled together. They're also intended to be throw away assemblies, so I wouldn't worry about repair.
I've been soldering for about 50 years, so I suspect I'm sufficiently experienced to have made all the usual mistakes (several times). It's not the lack of skill. I have no problem using braid on large objects with small heat sinks. I have nothing but problems using braid on small objects attached to large heat sinks. I this case, there's a small leaded capacitor, connected to a rather large copper heat sink of the power bus inside the PCB. You can see the effect when unsoldering the capacitor leads. The ungrounded hot lead comes out easily. The grounded lead is far more difficult. If the capacitors are near the CPU and on a power bus, then both leads are difficult. Braid is also quite suitable for unsolder connections where the solder is easily accessible and exposed to the braid, such as large xformer pins, terminal strips, wire terminals, some IC sockets, tube sockets, etc.
Also remember that this is for what appears to be a beginner at repair. It's easier to explain how to operate a solder sucker than braid.
I forgot to mention the desoldering bulb, another device that barely works:
The only good part is that it's great finger exercise (I play piano).
I recently purchased one of the contrivances:
It's a solder sucker hung on the back end of a hollow soldering iron. It took a while to discover what was wrong with this idea. The amount of vacuum generated is dependent on the unsuck to suck ratio of air volumes. With an ordinary solder sucker, where the tip is close to the piston, the ratio is rather large, thus offering a good vacuum. Not so with this contrivance, as the volume of the hollow tube adds to both volumes and results in much less vacuum. A larger diameter piston or shorter soldering iron barrel would have made it work better, but as it stands, the design sucks. 30 watts also seems underpowered, the tip is too big, and it takes 10 minutes to warm up. I haven't used it much, but I suspect that it will clog with dross near the entrance to the solder sucker.
True. However, I would rather use a guided missile (fancy desoldering station) than to go off plinking at the target (solder braid).
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
My first "job" in electronics was in the back room of my barber's shop who had a little hobby business repairing electronics odds and ends. It was where I learned how to solder. Especially after being told by one of the barber's friends that I soldered like his grandmother :) That was in
1971. I was 16.-- Live Fast, Die Young and Leave a Pretty Corpse
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