[Coco] Sort of OT: Recapping

[Richard Lorbieski]

Based on the photos, this is a multi layer IBM clone PCB with possible 
internal ground and power planes.

The problem is that the heat is being dispersed onto the ground (or 
power) plane and not enough heat is being applied to the solder.

This kind of rework requires more than a 70W soldering iron.

You will need a rework station with a heat gun and possibly a variable 
convection type oven.  A conventional oven could damage components on 
the PCB or melt some of the plastic parts. You will also need a 
soldering iron that is capable of reaching 900F and use a proper solder 
tip. Most consumer soldering irons usually reach 600F-650F.

I also recommend NOT to sharp knives or force the leads out of the PCB. 
This could damage the internal connections on the PCB.

The dark (baked) flux can easily to removed with a good flux remover.

On 11/27/2020 3:09 PM, Salvador Garcia via Coco 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
>