Should I fix/replace this Apple Power Adapter cord?
January 11, 2014 3:21 AM   Subscribe

Having successfully pried open my 85W PA-1850-02 Magsafe brick in order to fix (or possibly replace) the power cord, it doesn't look like the various repair tutorials/videos: the inside is full of a kind of white mastic/gunk. Is this perhaps melted plastic (from too much charging heat)? Is this a situation where the only (or the wiser) option is to shell out for a new brick?
posted by progosk to Computers & Internet (10 answers total) 1 user marked this as a favorite
Best answer: Looks like it's sticky at this point, right?

If so: not melted plastic, but some goo they added to your particular model to hold everything together. Just work around it.
Melted plastic most of the time gets discolored, and it would be brittle.

[and yay for you to take the effort!]
posted by Namlit at 3:59 AM on January 11, 2014

Response by poster: It's not brittle, and it's really the same white as the case's plastic; it's pasty/sticky, but doesn't really seem like glue. It just seems odd that it's not mentioned at all in other takings-apart...
posted by progosk at 4:06 AM on January 11, 2014

Best answer: I once bricked a Macbook (not just the DC-IN board but some part of the motherboard) during an attempt to repair the power-brick, I wouldn't do it again.
posted by lenehan at 4:12 AM on January 11, 2014 [2 favorites]

Yeah, I guess that the assembly of these things is spread out over a bunch of facilities and thus perhaps deviations happen. Otherwise it could have been a fleeting thing, about which the Apple repair people complained, or conversely, it's a new feature and the tutorials are older. But is seems like you're fine.
posted by Namlit at 4:13 AM on January 11, 2014

That white stuff looks like thermal grease.
posted by jmsta at 4:33 AM on January 11, 2014 [2 favorites]

Best answer: The material is a potting compound. Like an epoxy of sorts that is used to stabilize flimsy parts of an assembly, usually to prevent vibration fractures, etc. It's not heat sink compound, which is used sparingly and it usually the same stuff as old school sunblock (zinc oxide in mineral oil base). Heat sink compound would appear as a white, oily paint that never dries. It would have no volume... just be a film. Too much is worse than none, so your quantities are clearly not that. Potting compound is chemically inert to electronics, non-conductive and has documented thermal specs, but they are incidental to its main function.

Potting compound is usually on cables, caps, and anything where the leads and other mechanical parts are too weak to prevent vibration inducted failures. It is not intended to be easily removable, and in the case of these very dense switching supplies, they are not intended or designed for service. If they were, they'd be larger, more accessible, and would have other means of securing the parts.

It's not melted plastic. Anything that would melt it would melt the case. The case looks fine.

I don't bother fixing Mac bricks. Not economic to repair, generally. You really have to spend some time inside those things to appreciate how much Apple gets in those little boxes, all in the name of fashion. Impressive hardware. Not the most reliable part of the mac experience, though.
posted by FauxScot at 7:47 AM on January 11, 2014 [2 favorites]

I've replaced the cord on a Mac adapter before. In fact I'm using it right now. It's easy if you're good at desoldering and soldering; it's just two relatively thick wires. Just get the polarity right of course. The replacement cord should have metal connectors on the end on that should pop in the holes and take lots of solder for a good solid connection. Just make sure the holes are clean (I prefer solder wick to a solder sucker). Getting the shell back together is kind of tricky, though. I wound up with a combination of super glue around the edges and clear packing tape for reinforcement. However if you don't consider yourself good at soldering, maybe this is a project to skip.
posted by zsazsa at 9:12 AM on January 11, 2014 [1 favorite]

I've seen stuff like that inside quite a lot of things that were obviously never meant to be taken apart after initial assembly.

Given that you've got this far and that all you actually need to do to it is replace a cable, you might as well go ahead with that. When you're done, pick out as much of the gunk as you need to in order to make the case fit neatly back together, and replace it with a few good squirts of neutral-cure silicone bathroom sealant (must be neutral-cure, don't use the kind that smells of vinegar). A few drops of superglue (cyanoacrylate) in the case seam will stick the halves back together about as well as the original ultrasonic welds did.
posted by flabdablet at 10:21 AM on January 11, 2014

Best answer: Yep, ignore that stuff. Solder sucker/wick on the leads, solder the new cord on(look closely at that one you linked, the wires are the wrong colors. it might still be fine though). Note that there's 5 leads in the connector. And although only two main wires come out, i'm pretty sure the "shield" wire goes to the center pin. I forget exactly how it connects, but i'm fairly certain that's for signaling.

Reassemble the case with plastic-specific epoxy, like the gorilla stuff. Superglue or anything more "brittle" will just fall apart and not stand up well to the heat that comes out of these things.

By the way, i favorited the comment about fixing these things and slightly bumping something or there being slightly too much resistance, etc, and it burning out the PMU in the macbook. These bricks are under $30 on ebay, why not just buy a new/used one? Macsales has them for $49 too.

I decided these are never, ever worth repairing. I just throw them in the "to the pc recycling shop" bin at my work and order a new one for ~$25.

$5+ship for the cable plus your time. What is your time worth? more importantly, what is the risk of damaging the system worth?

When a new cord shows up, just slide over and epoxy some 2-3in long springs over the cord at both ends. It'll last the rest of your life.
posted by emptythought at 4:07 PM on January 11, 2014

Response by poster: Given lenehan's warning, the fact that the replacement cord can't be shipped to Europe, and the presence of an unopenable hard plastic white inner cylinder that the white and black wires are run through in my specific model of power brick (you can make it out here), I've decided not to tempt my fate. Thanks for the collective advice all the same.
posted by progosk at 9:08 AM on January 12, 2014

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