# de-soldering advice



## MTN REMODEL LLC (Sep 11, 2010)

I have no idea how to do that board/electronic work....

I had a relay go out on an oven... I ran it up to the local computer store and he resoldered it for $10 and 5 minutes.


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## Bud9051 (Nov 11, 2015)

Well, I'm extremely experienced in soldering and desoldering so you are in the right place. 
Are these caps mounted horizontally or vertically, sounds like horizontally if you can see the leads. But, one approach is to cut the leads leaving as much wire as possible and remove the cap. Then back to the solder sucker, but don't burn the lands. 

I use forceps and clamp then to the remaining wire and hold the board so when the opposite side is heated the weight of the forceps will fall away taking the remaining lead segment with it. If you don't have forceps a second person with needle nose pliers can gently pull while you heat. Don't pull too hard as you don't want to remove the land.

Pictures would help.

If vertical caps we use another approach.

Bud


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## TinyFargo (Jul 19, 2018)

They are vertical. I can't get either my solder sucker or my iron sufficiently under the caps to touch the joint at all... they're just mounted so close to the board. I've sucked the solder off from the underside but just don't seem to be making sufficient progress.

If I could get in there, I'd just clip the leads to caps to get the cap body out of the way and then desolder to pull out the wire, but the other components you can only kind of see in the photo are restricting my access.


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## Bud9051 (Nov 11, 2015)

Ok, now that we know what we are dealing with we move to plan B.
If you have sucked all of the solder off the leads and lands on the back side, put some back. Much easier to transfer the heat to the lead if you have some solder to touch with your iron. Then choose one and heat one lead while tipping the cap away from that lead. It should move slightly. Then tip it the other way while heating the other lead. Repeat and you will walk the cap right out of the holes. Then the solder sucker can pull the excess solder out and that one is done.

Tip for the solder sucker is it likes to have some excess solder to help suck it clean.

If that fails we do have a plan C but a bit more involved.

Bud

PS, bad caps usually swell at the top and sometimes shrink the blue plastic down the sides, I'm not seeing either. But you have new caps so proceed. Also note the polarity on those caps so you install the new ones correctly.


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## BrownEyedGuy (Oct 2, 2018)

TinyFargo said:


> They are vertical.


When you said they were tight, I assumed you couldn't move them, but those are easy to do. 

You heat the solder from the underside, and apply sideways pressure to the cap until the cap lead pops loose. Work back and forth, as necessary, until both leads are free.

Solder is very thermally conductive (obviously), so simply heating the underside of the board will also heat the top-side. 

Don't use your solder extractor until after the capacitor is removed. You need that only to open the via (hole) so you can insert the new capacitor into the board.

Keep in mind that the absolute worst thing you can do to the board is overheat it to the point that the wire traces delaminate. If you have a very low-power iron, make sure you heat the solder enough to fully flow both top and bottom puddles, and conversely, if it is a high-power iron, make sure you don't dwell too long before letting it cool back down.


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## BrownEyedGuy (Oct 2, 2018)

Bud9051 said:


> Ok, now that we know what we are dealing with we move to plan B.
> If you have sucked all of the solder off the leads and lands on the back side, put some back. Much easier to transfer the heat to the lead if you have some solder to touch with your iron. Then choose one and heat one lead while tipping the cap away from that lead. It should move slightly. Then tip it the other way while heating the other lead. Repeat and you will walk the cap right out of the holes. Then the solder sucker can pull the excess solder out and that one is done.


We were posting at the same time, but this is the same reason why I said to not use the desolder sucker until the cap is removed. 

Sorry for duplicating the same info.


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## BrownEyedGuy (Oct 2, 2018)

Bud9051 said:


> PS, bad caps usually swell at the top and sometimes shrink the blue plastic down the sides, I'm not seeing either. But you have new caps so proceed. Also note the polarity on those caps so you install the new ones correctly.


Yeah, I was also going to say the same thing too. I doubt that replacing these caps will correct the problem. 

What's the frequency of this "heatbeat"?


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## TinyFargo (Jul 19, 2018)

BrownEyedGuy said:


> Yeah, I was also going to say the same thing too. I doubt that replacing these caps will correct the problem.
> 
> What's the frequency of this "heatbeat"?


It was at exactly 1 Hz. I agree that the caps don't look bad, but there are a few other threads that I saw that indicated that these were the culprit for such an issue. I figured that I had nothing to lose by trying! A few bucks at Digikey and an adventure... :wink2:


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## BrownEyedGuy (Oct 2, 2018)

TinyFargo said:


> It was at exactly 1 Hz. I agree that the caps don't look bad, but there are a few other threads that I saw that indicated that these were the culprit for such an issue. I figured that I had nothing to lose by trying! A few bucks at Digikey and an adventure... :wink2:


OK, at 1 Hz, it's a resonance or discharge issue. Because these are powered subwoofers, I'd be looking for problems closer to (or at) the speaker. 

Play around with just touching different sized capacitors across the speaker and see how it affects the "heartbeat". 

============================
I never did figure it out, but back in college, when I would play one particular Pink Floyd intro that had a very deep frequency intro, my roommates speakers would "backfire" like all getout (but my speakers were unaffected). Every second or so, they would "pop" like a gunshot when they were fed this low frequency......I never bothered to fix it because they weren't my speakers....plus....it was fun as hell to hear. :devil3:


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## BrownEyedGuy (Oct 2, 2018)

Ooooohhhh! Now I remember why that story sticks with me after so many decades beyond college. My roommate's speakers were tuned for very low frequency, and they were sitting on the top shelf of the built-in wardrobe cabinets of the dorm. 

They created such massive resonance throughout the whole twin-tower dormitory building (the same building that the MN Vikings used to sleep in for spring training), that when we played that long-forgotten Pink Floyd song......


Engineering students on the far end of MY floor (1st floor) came running out of their rooms thinking there was an Earthquake. (SERIOUSLY, they did)
Students on the 2nd, 3rd, and even 4th floor called the front desk to complain.
Administrative staff on the concourse between the buildings (also 1 level below us), heard it and sent several security personnel up to our floor to find out who was doing it....we shut it off before they got there. :vs_laugh:
Our Resident Advisor was pretty cool, and knew exactly who did it, but all he ever said to us was, "don't do that again, or I'll tell them who it was." :vs_cool:


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## Bud9051 (Nov 11, 2015)

I was going to (at 3:30 am) look around at the board to see I could spot any other caps or other hi risk components but don't see the picture any more. I have no idea why. Can you repost that picture and maybe one of the underside, assuming the problem remains.

To trouble shoot "motor boating" I would be using an oscilloscope. Can you get or do you have a schematic of that board? Searching for something online but no luck.

Bud


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## TinyFargo (Jul 19, 2018)

Bud9051 said:


> I was going to (at 3:30 am) look around at the board to see I could spot any other caps or other hi risk components but don't see the picture any more. I have no idea why. Can you repost that picture and maybe one of the underside, assuming the problem remains.
> 
> To trouble shoot "motor boating" I would be using an oscilloscope. Can you get or do you have a schematic of that board? Searching for something online but no luck.
> 
> Bud


I haven't used a scope in ages... my home electronics usually aren't worth this much to not just replace them when stuff goes south. I chose to replace these caps because of many threads on the net, such as:
http://mrfxr.com/polk-subwoofer/

Nothing like shotgunning some parts!

If I don't get it working replacing those two caps I'll start posting pics and seeing if I can borrow a scope from somewhere.


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## Bud9051 (Nov 11, 2015)

Electrolytic capacitor are definitely a good place to start, I've replaced hundreds of them. Their primary problem is heat. If any are mounted next to power resistors or heat sinks their failure rate goes up.

Back in the big company days we had all Techtronic scopes. Out on my own all I could justify at the time was an inexpensive generic one, but it sure has served it purpose. I don't get much bench time anymore, retired, but do enjoy it when I can.

Let us know how the new caps do.

Bud


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## TinyFargo (Jul 19, 2018)

I used to be a software engineer in the aerospace industry and have used all sorts of really nice equipment over the years... but since I was software and not EE, I only sort of understood the stuff I was looking at.

Anyway, making progress... got the existing caps off. Having trouble cleaning up the pads enough to slip the leads on the new caps through the through-holes. I have tried using the desoldering pump to remove all the solder and I've also tried just gently pushing on the new cap's leads while heating from either side with the iron to try to get the leads through the solder that's there. Neither approach is working. How would you do this?

Like always, I find myself wishing I had some nicer tools...I used to work at a place that had solder vacs where the vac and the heat was all a single tool. The people who worked there were real artists.


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## BrownEyedGuy (Oct 2, 2018)

Heat the solder, and quickly tap the circuit board on your desk before the solder can cool.


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## bmwmerchant (Jan 6, 2019)

I use desoldering braid and flux.









Sent from my SM-A530W using Tapatalk


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## TinyFargo (Jul 19, 2018)

I GOT IT!

I switched to the thinnest tip on my iron - one that actually fit inside the through hole. I turned the iron down to a low temp that would barely make the solder flow and pressed gently on the hole from the bottom of the board. Meanwhile, I had the solder sucker ready to go held tightly against the surface on the top side (way easier since the caps aren't there anymore!)

As soon as I felt the iron start to slide into the hole, I pressed the button to suck the solder out from the other side. As soon as I popped the sucker, I immediately pulled the iron away from the board.

On a few of the holes it took a few goes at it, but I could tell it was taking a drip or two each time.

Now just need to solder it back together and hopefully it works again! :biggrin2:


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## TinyFargo (Jul 19, 2018)

IT WORKS!

:biggrin2::vs_OMG::biggrin2:

Replaced the 2 47uF caps only and it sounds AWESOME. I did not even realize how much I have missed the thump of a subwoofer!

The caps I used to replace are rated for a higher temperature and longer life than the ones I took off, so hopefully they'll last longer than the last set.

Thanks to all for your input and assistance!


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## Bud9051 (Nov 11, 2015)

The board you are working on is a multi layer board, at least top and bottom. To connect the layers they plate copper through the holes so they conduct electricity as well as heat, but be careful that little cylinder of copper can come out with too much heat.

When the solder puller can't seem to suck out the last little bit of solder, then add a puddle to each side, not too much. Then the flow when you hit the button on the sucker will pull the hole and land area cleaner. You'll also need to clean the solder puller more often do to added solder.

Good job,
And thanks BrownEyedGuy as well 

Bud


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## bmwmerchant (Jan 6, 2019)

Congrats. I do a lot of soldering and really enjoy it very relaxing. Make sure you have small fan to blow fumes away very toxic dont want to breath that in. An old computer fan works perfect. 

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## FrodoOne (Mar 4, 2016)

It is a bit late for this thread but using a fine pointed dental tool (such as some in this kit https://www.ebay.com/itm/Profession...m56aba58427:g:X5AAAOSwnwpcZih4&frcectupt=true)
is often a great help in de-soldering the "holes" in circuit boards, after a component has been removed.

Use a fine pointed tool, don't use too much force, apply the point to the centre of the hole, apply heat and allow the stainless steel tool to slide through the hole. Of course, solder does not stick to stainless steel.

(A dental mirror, such as in this kit can also come in handy!)


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