Desoldering Woes

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Drone
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Desoldering Woes

Post by Drone » Sun Jul 09, 2017 11:51 am

So, I got the replacement faders for my mixer, and set about replacing them, but I had a heck of a time with getting the old ones out.

Normally on a multi-pin part, if I don't need to keep it, I'll carefully cut the part out with snips and then desolder each pin. This time round I had one pin that just would not come out. I tried it all, flowing in more solder, using the braid, and the suction tool, trying to get it out with tweezers and my iron point, trying to poke it out with the old pin while applying the iron, it would not release. I checked it with my kids pocket microscope and it looked like a tiny bit of pin, but I wouldn't force it lest I damaged the board.

I had my desolder braid, a variable temp iron, a probe and some tweezers, but I could not get one pin out to the point where I put it back together with that pin bent out the way on the new part, in the hope it was unused (stereo fader on a mono channel).

Things I don't have are a little bottle of flux and a desoldering station, you think either of them would have helped? The thru holes were too close together on the fader for me to think of getting out a pin vise and drilling and 'landing' the hole with a rivet.

The mixer is back together, and working so far, but I worry I may need to go in and get this damn piece out. The other channel I replaced came out just fine.
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Post by Scodiddly » Sun Jul 09, 2017 4:21 pm

It's a challenge sometimes. My usual toughest customer is anything made by Aviom, who favor tight holes and mucho ground planes.

One time I finally gave up and just drilled out the offending gunk in one hole. Careful inspection can show whether you need to account for through-hole plating or not.

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Post by Drone » Sun Jul 09, 2017 4:27 pm

I was a tech for the first half of my working life, so you think I'd know, they were 60mm stereo ALPS faders (10k) and there are 4 pins at one end, and so dang close. Like I said I daren't drill it out, I used to have a little pinvise drill for this kind of thing, but the pitch of the holes is so close.

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Post by kslight » Sun Jul 09, 2017 7:12 pm

Did you try a solder sucking pump? Not the most precise tool, but I've had good luck making these work when everything else fails.

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Post by Drone » Mon Jul 10, 2017 9:40 am

Yes, sorry, I had the pump too. Just one of those button press one shot ones.

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Post by Snarl 12/8 » Tue Jul 11, 2017 10:52 am

I have two of those pumps and one of them works way better than the other. The one that looks like the one in your picture is the worser. The more plasticky one that I got, ages ago, from Rad Shack works way better. YMMV.
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Post by vvv » Wed Jul 12, 2017 9:24 am

I have one like that pictured; I've been considering modding it into a zip-gun. :twisted:
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Post by The Scum » Thu Jul 13, 2017 3:33 pm

So is the solder joint in question melting reasonably well?

One thing that can trip desoldering up is pads on ground pours, or other metal features that just absorb the heat, and keep the solder from flowing.

In that case, preheating with a heatgun can help - if the surrounding areas aren't cool, they won't draw the heat away so quickly.

Sometimes a dab of flux helps...if the solder is oxidized, the oxide prevents heat transfer, and flux clears the oxide. If you're soldering very much, a flux pen is worth having around.

Cheap springloaded solder suckers are junk. The good ones come from "Soldapullt" - get the big one.

http://www.edsyn.com/product/DHT/DS017.html

I've got a Pace desoldering setup with a vacuum pump. It's even better than a Soldapullt, though also 50x the price.
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Post by Jim Williams » Fri Jul 14, 2017 8:20 am

If you can't swing a Hakko pump, buy some 'Chip-Quik" desoldering low temp solder. That melts at around 250 degrees so it will wet the old solder and lossen all of it up for easy extraction.
Digi-Key sells the kit for about $14.
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Post by Drone » Fri Jul 14, 2017 8:34 am

Yeah, that was what got me, the solder would melt fine, but the piece was like caught somehow, I could get it to wiggle in the hole, but couldn't get it out in either direction.
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Post by The Scum » Sun Jul 16, 2017 12:44 pm

So if part of the problem is that it's hard to get the pin out because there's a bunch of solder making it hard to tell how to get it out, by all means remove that solder.

Depending on how much solder that amounts to, bigger & stronger tools might be required. Small job = wick, medium job = big sucker, big job = industrial heat gun (or blowtorch) & a sharp whack.

And I can vouch for Chip Quik. It does what they claim.
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