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Wrecked Pad Recapping on a Macintosh Portable

raoulduke

Experienced Member
Joined
Jan 14, 2015
Messages
356
Location
New Jersey
I apologize for posting this so soon after the other Portable restoration thread. I've had mine sitting around for a few years. I recapped all but one capacitor a year or two ago, and then I let it sit. At the time, it didn't seem to work it all.

When I broke it out recently, it definitely turned on and I got a display response, but no response to the floppy I inserted. I am hoping that - if the issue is a capacitor problem, that the culprit is (only) certainly C4, which I thought I had gotten to stay in place, but which has a serious problem with its + pad (I don't think I caused the problem).

I couldn't think of a better place to post this question, but I was hoping people have opinions about how to best bypass or fix this? Personally - because the space is very very tight and difficult to deal with - I was thinking of attacking a wire at least to the exposed copper where the dead pad is, and possibly to the other pad also to make it easier to work with. Does that sound make sense? Thanks.
 

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Just scrape away some of the trace that goes to the lifted pad and put the capacitor across that and the remaining good pad. It looks like there's plenty of space to do that.

You could also run a bodge wire, but the capacitor won't sit flat, which may lead to connection issues.
 
I considered the scraping possibility - in fact the dead trace is itself basically exposed copper anyway, but I can't get anything to stay on it, and it's such an enclosed space I don't think I can expose and then actually work on it. But I agree the bodge wire idea presents concerns. I might probably tape the capacitor somewhere(?).
 
You generally need to scrape the copper trace with the end of the soldering iron for a bit to get rid of oxides and other contaminants before the solder will stick. You can relocate if you really want to, but I wouldn't put it too far away to avoid interference.
 
I'll post a pic of my attempt. At this point, it's been sitting on a table in my room for months, so I need to just try something. But I was thinking of maybe 1" of wire - because getting the wire to stick will be much easier than seating the capacitor. I'll do some cleanup (and maybe scraping) first. Thanks again
 
What did you take the photo with a gameboy camera? Just kidding.. you got to clean the sludge off to get a good view of whats left underneath. I do plenty of Destroyed mac board repairs. Even if the pad is gone you can find where the trace goes to a via or another component and run a small bodge. I would wash the board in the dishwasher first. ITs good at taking off corrosive gunk. Rubbing alcohol and a toohbrush goes along way too.
 
There's no sludge. I tried to take it using a tripod setup, but I do not have a great setup for taking very high-quality pictures. I did wash the board before I first recapped it years ago - most likely first with scrubbing bubbles on select spots and then in the dishwasher.

I can't get the solder to stick on the broken pad... I currently have three wires hanging off each of the other pads (for the 2 cap spots) but i cannot get the fourth to stick on or near the broken pad (which should still be conductive, since the copper is exposed). I'll wipe it off with rubbing alcohol, but I don't think that will help the solder to stick.

Any suggestions?
 
the picture looks like there is sludge but the picture is terrible. I think you best best is flush cutters at the base of the can and use flux and a soldering iron to remove the legs (which may just tweak off on thier own due to corrosion). Use flux and braid to clean up the pads, new solder can be applied as well.
 
When surface mount electrolytic capacitors leak, they cause to soldering to oxidize heavily to a grey compound. The oxides are thermal insulators that make it very difficult to apply heat to the solder join and melt the residual solder.

So the first move, before attempting anything, is to scrape off as much of the grey oxide as possible. Once bare solder starts to appear then apply a liberal amount of fresh solder to each of the terminals one at a time. Once that is done it then requires two soldering irons, one in each hand to simultaneously melt both of the capacitors solder terminals, then manipulating the soldering iron tips, apply a small amount of torque (turning force) and the capacitor will separate from the board without damaging the tracks.

There is all sorts of poor advice on the internet about on how to remove surface mount components, typically IC's but sometimes capacitors. While it is reasonable to cut the pins on a DIL IC for pin at a time removal, it is a disaster for surface mount parts.

Cutting the surface mount part's pins, or cutting up the surface mount capacitor for removal, is very bad idea for both capacitors and surface mount IC's and risks lifting tracks from the pcb.

For example in the case of surface mount IC's, for removal without track damage, it requires one of two things, either the correct size de-soldering tool for the particular size IC (which most people don't have on hand) or there is only one other method safe for the IC which pushes the tracks toward the pcb surface when the solder is melted, using enameled copper wire (see attached picture) It is good for this method to use grade 2 enameled copper wire, not poylsol or self fluxing wire. Heat guns in my opinion are a disaster and generally fry everything in the surrounding areas and should be avoided.

In cases where I have repaired missing or damaged tracks I generally use very thin shim brass, or the stick down copper pcb repair foil.

One reason I don't tend to buy repaired or refurbished vintage gear is I always get horribly disappointed with the poor de-soldering & soldering skills and the track damage from people that have previously done repairs, it drives me up the wall. I like it when nobody has touched the pcb and I can do it myself without adding any track damage.
 

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There are also low-temp solutions, such as Chip-Quik for component removal. Basically a low-temp fusible alloy that reduces the melting point of solder to something less harmful to the PCB. I use the technique to remove TQFP ICs.
 
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