Thruhole cap desoldering advice (multilayer PCB)

[mcinque]

In some cases, even with a good desoldering gun, you won't be able to pull out easily the pins soldered to groundplanes.
Try to preheat the spot with a hot air gun, like in smd.

[Phaedrus]

I grip the cap from the bottom with a pair of pliers. Then I apply a solder ball to my iron and wick it back and forth between the solder points in question. I get both molten at the same time, wicking back and forth with the iron, while pulling down with the pliers, rocking the cap back and forth a bit. It usually pops right out. Then I pick up the solder with solder wick and clean with isopropyl. Don't do this if you want the cap to still be usable; the pliers usually dent them. Practice on a board you don't care about first, because if your heat is too high you can scorch the PCB or lift a trace.

I've recapped several PSUs that way, including some 4 layer DC-DC boards with solid ground layers. Never done it on a GPU or motherboard though.

[lpc32]

Hot air gun! It's gone the whole spectrum from flux all the way to that.

Anyway, I broke off the cap (hopefully no damage to the via) with repeated tilting in opposite directions. Pushing with a needle, and with some extra added solder, I was ultimately able to get the remains of the leads out. Then wicking, and more needle pushing, to try to get the hole clean. While I was sometimes able to see the beginning of a hole, it's doesn't clean well and mostly remains clogged.

I'll get a solder sucker and see how that goes. Maybe also some flux (any eBay suggestions?). How likely is it to find alternative tips for a generic iron with a two-sided screw holding the tip (not threading near the handle)? A chisel shaped one might be more practical.

[GiskardReventlov]

+1 on cutting the cap off and leaving the leads and soldering the new cap onto the leads. If I liked the graphics card I would not want to disturb, mechanically or thermally, what's there. Repeated heating seems like a bad idea to me. So I guess it depends on how much you like the board.

[lpc32]

For future's sake, and in expectation of fishy capacitors or just side effects due to changing the type, instead of soldering directly I'm going to try using this:

[Monkeh]

Those have a tendency to eject round leads..

[mariush]

Also, switching power supplies (including DC-DC converters like the ones in video cards) are often designed to put capacitors with as little wire as possible. More than a few mm of extra lead is not recommended, because those leads act like an inductor in series with the capacitor.  That's why capacitors are often very close to heatsinks and switching ICs, to minimize current loops, reduce EMI etc etc.

Those headers also introduce other problems.. additional resistance, poor contact, longer leads, issues with two different metals... etc

[chibiace]

id use a cheap solder sucker to get all/most of the solder out of the holes then if needed heat both leads and wiggle from the other side.
to clean up the holes probably reapply solder and suck out.

[lpc32]

Monkeh, they seem to grip quite well, at least the ones I have.

mariush, I suppose it's slightly less ideal than direct soldering, but any idea if it matters in practice? Assuming it *seems* okay, what latent side effects should I be looking for?

chibiace, yeah, will try a sucker. It's occured to me, and maybe was alluded to earlier, that it's probably also more difficult to desolder with 30W because it's lead-free.

[Monkeh]

This is what happens with most of the methods described here, sooner or later:


Especially when you have a little 30W iron. I strongly suggest getting a more suitable iron and preferably a high power desoldering iron if you plan to do this sort of thing.

[lpc32]

The plan is to get a better iron once US logistics allow.