[Coco] Sort of OT: Recapping

[Dave Philipsen]

The problem is evident from looking at the photos. Your board has huge sections of ground plane around the capacitor pins that are sinking the heat away as you’re trying to desolder them. The key is patience. The soldering iron will have to stay on the pin for a much longer time because the copper ground plane must be heated up sufficiently enough to get the pad up to the temperature where the solder will melt. If you’re really having a hard time with it, one trick would be to cut the pad free from the ground plane by circumscribing it with something like an Exacto knife being sure to cut through the copper ground plane to the fiberglass board below. This will detach the huge ‘heat sink’ from the capacitor pad allowing it to be easily removed. After replacing the capacitor, remove some of the solder mask on each side of the cut, drop a piece of small diameter copper wire into the valley created by the cut, and flow solder over it reattaching the heat sink/ground-plane to the capacitor pin. 

Also, the rosin from the solder is not permanently staining your board. When the job is all finished, use some flux remover to get it off. If you’re using “no-clean” solder then that’s not even necessary as the flux poses no long-term danger by staying on the board (doesn’t look pretty but won’t hurt anything). 

-Dave Philipsen

> On Nov 27, 2020, at 3:11 PM, Salvador Garcia via Coco <coco at maltedmedia.com> wrote:
> 
> I am trying to recap a motherboard which is not from a CoCo, but I thought this subject might be of interest to the CoCo community since recapping seems to be a fairly common occurrence in the vintage computer community.
> 
> I noticed three bad caps on the MB. I have done recapping before, so no big deal, or so I thought. My soldering irons, 25, 30 watts, would not melt the MB's solder.
> I got a Weller 1010 (70W) and this helped. I managed to remove the caps, but I still had a hard time melting the solder and two of them came apart and pieces of the pins (3 to be exact) are still in the through hole. Suggestions included applying clean solder and flux which I did. The clean solder helped, but the flux only left a dark stain on the PCB, so I discontinued its use.
> I can't melt the solder from three of the through holes where the pins are located. I've provided links to pictures. One of the cap's pins can clearly be seen sticking out of the MB for the cap in front of the choke (or inductor, not sure). The fat cap behind the choke is the one that I managed to successfully replace.
> I applied heat to the solder pad and tried to push the stuck pin with a fabric pin (the kind used in new clothing to hold the folds), was unsuccessful. I thought about grasping the protruding pin on the solder side, but did not because I figured that the pliers used would dissipate heat and make it harder for the solder to melt.
> In one case, I ended up using a very fine hand drill bit to remove the last remnants of solder from the through hole. This won't work where the cap's pins are still stuck in the through hole.
> At this point I've used up my options (and patience). Does anyone have any recommendations on how to get the stuck pins out? Hopefully this discussion will be fruitful to other recapping their CoCos and other computers.
> Links to pics follow, thanks much, Salvador
> 
> Caps. I am replacing three caps. The fat one in the back (behind the choke or inductor), which is already replaced, the smaller one in front of the choke, and the front left. The MB did not have a cap at the front right location. Note the cap's pin still soldered to the MB (in front of choke).https://drive.google.com/file/d/1heHQ3TfpMVcubUvvcUYxxFCOvEn9woKl/view
> Solder side, The dark spots are from the flux that I applied to determine if this would help to melt the solder.https://drive.google.com/file/d/1bLeOGqPTrGhhm3Xiyt7DGKq3Av_4BZ9O/view
> 
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