First shot at MB recap. Ugh!

[bobbyrae]

I have done some recapping in the past (power supplies and old stereos) and thought I was pretty good at it so am thinking of recapping an ASUS A7N8X motherboard. I've got one of these that's worthless and one that can probably be recapped, so I thought I would try removing some on the bad one. Just to see how it goes. Per the advice here.

My soldering station is a Hakko 936, which is 65W, and I figured it would work fine. It seems not!

If these caps have pads they are so small as to be almost invisible. At one point I became convinced there was no actual pad, just solder in the via. Is that possible?

Anyway, it was surprisingly hard to get the negative lead out on all three that I tried, but the pos one came out pretty easy. Weird, huh? I found myself holding the tip on there for almost a minute waiting for the thing to finally get loose, and then the lead seemed to be so tight in hole that I really had to pull. And yes, I know that it not advised, but it seemed the only way.

I must have spent about 15 minutes getting each one out, and then later trying to get the hole opened enough to put a new one in seemed like near impossible.

Basically, these holes seem impossibly tight. I was noticing the old cap had leads that were slightly thinner than a new one of the same value. I am talking about just a few thousandths of an inch (I measured) and it was making a difference!

So I am wondering if you experts have seen holes being this tight, and if there's some trick I haven't found in the FAQ here, or should just I just give up?

[clearchris]

Re: First shot at MB recap. Ugh!

The large ground plane wicks heat away from the hole. Lead free solder doesn't help.

If I'm having a hard time, Ill preheat the area with my 858d hot air station.

[mariushm]

Re: First shot at MB recap. Ugh!

Gently twist the capacitor at the top back and forth (by just a few degrees) until the leads weaken and they break. It can take up to 30-50 small twists back and forth, patience is key. Alternatively, just use some pliers to cut the old capacitor body close to the leads.
In both cases, you'll end up with a few mm of leads above the pcb.

This way, the leads and the aluminum foil inside the capacitor will not absorb as much heat so desoldering the leads will be slightly easier.

Get some leaded solder and ADD leaded solder to the bottom of the board where you have the tiny pads and leads - by adding leaded solder you decrease the melting temperature of the lead free solder they used, and you increase the surface area that your tip touches, so heat will transfer better to the through hole and the lead.

When you feel is right, grab some tweezers and from the other side, grab the lead and PUSH it through the hole. As the wire goes though, the lead will wick the solder on it so the hole should stay relatively clean.

[momaka]

Re: First shot at MB recap. Ugh!

The key to making desoldering easier: flux. Either gel or liquid will work. Radio Shack should have some if you really need it fast. Avoid plumber's fluxes, though - those are too "aggressive" and may corrode the board traces.

What you to is first put flux on all of the joints you want to desolder. Next, heat up your iron well and put a big blob of solder on the tip. Finally, use this method (commonly known as the "rocking" or "walking method) to remove the caps as you heat each leg.

Once you're done removing the caps, there are many ways to put the new caps in. Some people prefer to clear the holes clearly either with wick or desolder braid, vacuum pump, or just a plain needle (stainless-steel coated or completely made of stainless-steel a must). I prefer the cheap cork board tacks/pins that you hang posters with. Basically, I hold the board vertically, heat the pad/via I want to clear with the soldering iron, and poke through on the other side with the cork board tack. I don't fully clear the hole - just enough to make indentations in the solder. After this, I pre-cut the leads on the new caps so that they are trimmed to proper length before being installed on the board. Then I position the cap over the spot it needs to go (with the half-cleared holes on the board) and use the "walk" method sort of in reverse - i.e. just push the cap on top and heat the legs one by one to slowly "walk" it in its spot.

Once the new cap is soldered, I then apply flux again on its solder joints and retouch them with the soldering iron again to make sure they look nice and not too blobby.

With your iron, you should probably have the temperature set between 350 and 400C. Or may need to bump it a little higher, I don't know exactly. I've only used cheap 936 "clones" and variants, and those need lots of cranking up to keep the tip hot enough for motherboard work.

[ron350]

Re: First shot at MB recap. Ugh!

Willawakes tutorial also works.

https://www.badcaps.net/forum/showthread.php?t=485

The brand and part # of the electronic solder you use can make all the difference in the world.

[larrymoencurly]

Re: First shot at MB recap. Ugh!

The key to making desoldering easier: flux. Either gel or liquid will work. Radio Shack should have some if you really need it fast. Avoid plumber's fluxes, though - those are too "aggressive" and may corrode the board traces.

I once found regular non-corrosive rosin flux in the plumbing dept. of Home Depot. It was cheaper than local electronics supplies.

[momaka]

Re: First shot at MB recap. Ugh!

I once found regular non-corrosive rosin flux in the plumbing dept. of Home Depot. It was cheaper than local electronics supplies.

It's possible.
The reason I never recommend Home Depot is because many of the fluxes there are active ones (i.e. the kind you don't want). Easy for someone new to grab the wrong one and hose their board. But yes, now that you mention it, I think I have seen rosin RMA flux in Home Depot as well.

[Agent24]

Re: First shot at MB recap. Ugh!

I have done some recapping in the past (power supplies and old stereos) and thought I was pretty good at it so am thinking of recapping an ASUS A7N8X motherboard. I've got one of these that's worthless and one that can probably be recapped, so I thought I would try removing some on the bad one. Just to see how it goes. Per the advice here.

My soldering station is a Hakko 936, which is 65W, and I figured it would work fine. It seems not!

The Hakko 936 is a little old now and there are some better irons available from JBC and Metal etc but the problem is not so much the iron but the board itself and method used.

Motherboards and any other multi-layer board are much harder to work on than single layer PSUs etc, because they suck the heat out if your iron very easily. Preheating such boards either in a small reflow oven or with an IR or hot air preheating machine can help a lot.

If you have a SMD rework station you can use that for preheating as clearchris suggested. Use a big nozzle and move it around so you don't overheat anything and you don't just heat in one place which won't help much. If you don't have a hot air tool, a hairdryer can work quite well too. Avoid using a heat gun like you would for paint stripping unless you can adjust the temperature down to something sensible as these are pretty much overkill - unless you want to quickly remove something like a CPU socket from a board and you don't care if you toast the PCB....

Adding leaded solder if it's a lead-free board can also help. It can help if you use a solder sucker (with low suction!) or solder wick to remove some of the lead-free solder and then add more leaded. Chipquick solder is even better but this is expensive.

My current method uses a Den-On SC-5000 (Similar to Hakko 808) powered desoldering tool and on multilayer boards I add extra leaded solder and preheat with hot air.

Previously on motherboards I used an iron with a conical tip to get right in the hole (you can feel it go in when the solder melts) and a manual desolder pump on the other side to suck the solder through and out. Preheating would likely also help. This only works once you remove the capacitor first with the "heat each lead and wiggle it out" method.

If these caps have pads they are so small as to be almost invisible. At one point I became convinced there was no actual pad, just solder in the via. Is that possible?

Yes, some are very small. Not non-existent, but very small, especially compared to boards in power supplies etc.