Caps on multilayer boards

Assuming they're radial (or you wouldn't be asking), bend and wiggle until the legs fatigue, then solder to the pads?

Or drill in from the top wearing eye protection?

Cut (Dremel?) the can all the way round near the bottom?

Cheers

layer boards so the remaining legs can be soldered to? I have some kit I do n't want to extract from where it's fitted, with bad caps. Only the through hole component side is accessible.

Two soldering irons and a helper to pull it? (or push it out with a gravit y assist.)

George H.

Pliers, blowtourch?

I don't know what I'd do with the blowtorch, I only have access to the topside. I assumed pulling with pliers might kill the PCB, but I may easily be wrong there.

NT

It sure might. If wiggling doesn't work, can-opening sounds like the ticket. If you have a board that's known to be dead anyway, you could try out a few techniques.

Cheers

Phil Hobbs

tilayer boards so the remaining legs can be soldered to? I have some kit I don't want to extract from where it's fitted, with bad caps. Only the throu gh hole component side is accessible.

ity assist.)

What would I do with the soldering irons? Heat the capacitor can? I'm assum ing you understood the question.

NT

It's running but shuts down often, and I want to avoid risking the board. Cutting the can open with cutters is probably the best bet, I can't see soldering irons being useful.

NT

This seems like a mistake. Use a soldering iron with lots of copper in the tip, for good heat conduction. Apply tin-lead solder to the joint to dilute the (presumably) lead-free solder. You can then use a solder sucker to remove as much old solder as you can, and re-apply tin-lead solder. You need solder in the joint to conduct heat. Then, heat the joint and work the cap to pull the lead back a little from that hole. Go to the other lead and do the same. Each time, you can pull the lead farther, it only takes 3 cycles to completely remove the component. Then, apply tin-lead solder, and you may have to use TWO soldering irons, one on each side of the board, and you can clear the solder from the holes. Then, solder in the replacement.

I've done this on a number of PC motherboards. It is fairly tedious, but only takes 5-10 minutes per cap.

Jon

ultilayer boards so the remaining legs can be soldered to? I have some kit I don't want to extract from where it's fitted, with bad caps. Only the thr ough hole component side is accessible.

avity assist.)

uming you understood the question.

Sorry I did not understand. If wiggling doesn't work harden and break the leads, then as per Phil, de-cap it. (Dremmel, grinding wheel and eye proection)

George H.

I trimmed all the solder-side suggestions :-). Way back when I was first learning how to solder onto pcb's I did some destructive testing on dead stuff just to find out how delicate things were, including ripping some radial electrolytic caps off of boards. Now, these boards were 1970's vintage, 2 layer, definitely thicker than 1/16", with nice thick, wide copper traces and through hole plating. I just pushed sideways on the top of the cap perpendicular to the line connecting the leads, to maximize the leverage. Most times the leads started pulling through the capacitor body to give me 1/8-1/4" of slack, and then I could either reach in with little diagonal cutters or bend back and forth until the leads broke. If it is working but you have the cap past maybe 30 degrees from vertical and still need to pull more lead out of the cap, stop and put a small screwdriver or other wedge under the cap on the side you are pushing towards and then push some more. That keeps the leads as straight as possible so they come out of the cap with minimal force. Some were tight to the board or wouldn't loosen up, and some of those I still managed to wiggle enough to break the leads but some did rip traces and through-hole plating off of the boards. Naturally since this was a test I'm sure the success rate was much higher than it would have been if I needed to save the boards :-). You will have to look at your board and decide how rugged you think it is. Multilayer is probably a good thing, since the plated through holes should be longer and thus more rugged. Otherwise I think your only other option is to start cutting with a Dremel because I don't think you could gnaw through with wire cutters. Practice on a free cap to see how bad it will be. If you have room beside the cap I would use a cut off disc and cut maybe 1/16-1/8" above the board, just cutting the side wall all the way around if you can. Then you should be able to pull up on the cap and start the foil unraveling inside until you can reach in with small dikes and cut it free. If you have access to one side cut a line across the top and down one side to split the can open, and then start peeling. You're going to make a mess with electrolyte and little metal bits on the board so cleanup will be critical and may be more effort than just giving in and dismounting the board. Oh, the caps I was successfully destroying were in the 1/4-1/2" diameter range, rated maybe 6.3 to 35VDC. I tried a couple of big AC caps, over 1" diameter and rated at least 125 VAC, and the leads and cap construction were way too much for the pcb so no joy at all with them. I ripped maybe a dozen little caps off of a couple of scrapped TV boards, so more than one but not a huge sample size; it was a few minutes of good fun while I was supposed to be throwing away some junk :-).

----- Regards, Carl Ijames

Try this video. This guy is pretty good at repair.

e topside. I assumed pulling with pliers might kill the PCB, but I may easi ly be wrong there.

Cutting the can open with cutters is probably the best bet, I can't see so ldering irons being useful.

Is this a computer motherboard? If so a half fast repair technique isn't wo rth the bother. Just chuck it out. BUT To repair it you need a GOOD solderi ng iron and quite possibly a hot air soldering tool to to help your solderi ng iron. If the board has an internal power or ground plane without thermal reliefs, you won't be able to get enough heat through the lead to melt the solder all the way through. The hot air tool will help immensely. I've don e it this way several times with 100 % success.

Looks like you actually read the question, unlike a lot of replies. But most times isn't good enough here. I'll just do what I initially thought of and chew up the cap. Thanks everyone.

NT

Here's one method for removing SMT electrolytics that requires no soldering: (8:33) Fast forward to 4:00 if you're in a hurry.

They're through hole caps. I'll just chop them up.

NT

I just knew that would be too easy.

I do quite a bit of "recapping" of motherboards with bulging caps. These are the result of alternately heating each lead and "rocking" the electrolytic away from the PCB: However, that requires access to the PCB circuit side, which you indicate is inaccessible.

These days, I chop off the can and pull out the leads one at a time, with a little help from an antique desoldering station: Again, this requires access to the PCB circuit side.

Occasionally, I try to extract the leads from the component side. The desoldering tool will not transfer enough heat through the PCB to melt much of the solder on the circuit side. To get decent heat transfer, I have to add additional solder from the component side, which hopefully will transfer enough heat to the circuit side to allow extracting the leads. Even if that works, there's usually some solder splatter or dripping on the circuit side that needs touchup.

Also difficult is soldering a radial lead electrolytic to the PCB from the component side. You have to get the soldering iron tip under the can of the electrolytic, which implies that the electrolytic is elevated from the PCB at least the diameter of the soldering iron tip. If you can do it without melting the covering on the electrolytic, and nobody complain about the elevated capacitor and the aesthetics of crappy soldering on the circuit side, you might get away with it.

If I'm really desperate, and don't care what it looks like, I leave the remains of the original two wire leads soldered into the PCB and just tack solder the replacement electrolytic to wherever it will fit. I commonly do this when I don't have the proper can size or lead spacing. It's ugly, but works.

My apologies to John S. for posting the same URL. I messed up the read before write ritual.

I've done that last one at times. As long as it works. I tie the cap down so it's not unreliable mechanically.

NT

long nose pliers: crush and pull

tilayer boards so the remaining legs can be soldered to? I have some kit I don't want to extract from where it's fitted, with bad caps. Only the throu gh hole component side is accessible.

Too risky to the board.

I found chopping the cap up not effective, by the time I was down to the bo ttom its leads had snapped off from fatigue. The PCB pads are then so small , and their visibility so obscured by soldering iron & surrounding parts th at I can't solder anything onto them. Fwiw the thing works just as well wit h the bad caps missing.

It looks like I have little option but to dismantle where this thing is and get it out. Ah well. When I have yet another tuit.

NT