Solving 50Hz buzz/vibration/shock on Macbooks. 10

Apple has definitely dropped the ball, literally everyone I know with a Macbook complains about the “buzzing” or “vibration” and “pinching” or constant electric shocks they receive when using the device. I’m not sure how this happened, considering how well built and thought out their products are in general. While many an armchair-expert will probably scoff at this solution, this is a very widespread problem that Apple has failed to address and I needed a solution that gets the job done in the real world.

Apple AC/DC adapters are a double insulated floating output design, but they also come with an earth connection and in the longer cable that comes with Macbooks the earth is indeed connected and there’s no issue. If you unclip the longer cable and use the wall-wart style attachment (that also comes with the Macbook) instead, the adapter will no longer be earthed, and you’ll start getting receiving shocks.

I verified what this was by using a multimeter to measure the frequency from the case to the ground, and it is indeed 50Hz. While this is not necessarily due to a lack of earthing per se (in theory these power supplies don’t need to be earthed, which raises the question of why Apple decided to earth them on the longer cable), if the adapter is earthed the problem disappears, which is better than being shocked all the time.

While the longer cable that came with my Macbook had the earth connected, the smaller one did not, so I connected it to stop the issues.

Apple’s Macbook line come with two options for connecting the machine to a power supply. The first is a long extension cable:

The second is a smaller plug (plug type will vary depending on your location, this one is for Hong Kong):

The long extension cable has a proper earth socket which is connected and works, the second smaller plug however does not. It does have the earth pin, but this isn’t connected to anything inside the plug. When using the second smaller plug, users will experience a “buzz” or “current flow” when using their Macbook. This is actually a 50hz signal which is being earthed through the user’s body instead of through the electrical outlet. It can also add a 50hz hum to recorded audio, or audio played through the 3.5mm audio socket.

You’ll notice that the Macbook power adapter has a shiny metal disc as here:

That metal disc is the earth connection for the AC/DC power supply. You’ll also notice that the longer power plug has a metal contact where the metal disc slides into the plug:

The smaller plugs do not have this extra connection and are not earthed, which is why your body becomes the defacto earth connection.

You could play it safe by always using the longer power cable which is earthed, but when travelling etc it can be far more convenient to use the smaller plug, it’s unfortunate that doing so means your body becomes the earth connection. Fortunately, this can easily be fixed by any mildly technical person without even using a soldering iron. This mod will ground the Macbook, and current will no longer use your body for grounding.

Warning: if you aren’t confident about doing this, don’t. Mains electricity is dangerous and if you do something wrong, it will kill you. I do not accept any responsibility for any consequences of following this guide, I’m simply sharing how I chose to solve this problem.

1. Drill a hole through the power plug directly behind the earth pin.

When you do this, you’ll notice that the earth pin is not connected to anything. They could have made it from plastic and had the same effect. Use something strong and relatively sharp to scrape/scratch the back of the earth pin (for a better connection). I used a screwdriver. It’s better to go overboard with this step, look into the hole with a light and make sure you can see shiny scratches all over the top of the earth pin.

2.Drill down from the top of the plug, into the slot where the earth disc from the AC/DC converter section slides in.

3. Take some aluminium foil (not a good choice of conductor under usual circumstances but will work for our purposes) and wind it around the inner part of a ball point pen, make sure it’s tight. Be generous with the amount of foil you use, it would be difficult to use too much. Slide it off the pen, and twist up very tightly. It needs to be around 4cm long. Then fold it over to make a “V” shape as in the picture below:

 

4. Get some stiff, uncoated wire. Coat-hangers are too thick for this, a very thick paperclip will work, or some gardening wire. Poke it through the hole in the earth slot, all the way out the top of the plug. Put a small 0.5cm long bend at the tip of the ‘slot’ end. This is the part that will make contact with the earth disc.  Pull the wire through from the top of the plug so that only the 0.5cm section is visible in the slot.

 

Pull the wire fairly tight and bend it over the top of the plug to keep it in place.

 

5. Take the aluminium “V” and push it over the wire as shown here:

Push it all the way in so it is flush with the surface. Keep the wire tight while you do this.

6. Use tinsnips to cut the wire at the top of the plug as close to the exit hole as possible. Then use something solid to ram the aluminium foil down directly into the earth pin. Ram it in as hard as you can, you need a good connection. When you do this, it will pull the remaining wire from the top of the plug as you can see in the picture below:

 

I used the tip of some needle nosed pliers to ram the aluminium foil into the plug, but anything strong and blunt will do.

Notice how the wire is now down inside the plug, not directly across the hole as it was before. Note that the smaller hole visible in this picture between the slot and the large hole is not needed, this was an exploratory drill hole only.

 

7. Test the continuity of the connection with a multimeter, or any kind of circuit tester. Simply connect one probe to the earth pin, and the other to the earth slot where the 0.5cm of wire is sticking out. If you don’t get a connection, try ramming the aluminium foil harder or taking it out and repeat step 3 with more foil.

8. Fill all the holes in with putty. Get as much putty in there as possible to hold everything in tight. When I pushed putty into the big hole it started squeezing through the small hole in the top, that’s how hard much force you want on the putty. I used this Selleys “Knead It” because I had some at home, but any two part putty will work.

 

The final result:

 

If only Apple would just earth all of their plugs. I get it, you want a nice internally earthed power supply, but considering how many people are affected by this, and have been so for a number of years through many iterations of the Macbook, couldn’t you just bite the bullet and use a traditional earthed power supply instead?

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10 thoughts on “Solving 50Hz buzz/vibration/shock on Macbooks.

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  4. Reply Bernie H Nov 1, 2014 5:15 pm

    Sometimes adding mass to an object will change its resonance frequency which could stop the buzzing. I found that coils and transformers vibrate mechanically at 50 or 60 Hz due to changing magnetic flux. I found that putting conformal coating between the coil and core will minimize the sound. This works well on switching type power supplies.

    • Reply Martin Nov 27, 2015 8:28 am

      This is no accoustic hum. It is a small current from the mains voltage, which is coupled through the filter capacitors. So the only solution is to drain it through earth ground.
      But having already drilled so many holes, I would have used some proper copper wire to make the connection. When aluminium oxidises, the oxide is a perfect isolator. Copper does not oxidise so readily and its oxide is still somewhat (semi)conductive.

  5. Reply cghera Nov 1, 2014 10:04 pm

    Finally an article that references this issue, that made me think I am the only one having it. Interesting hack-solution applying only to UK plugs however and not the rest european without ground (the short ones). On the long one I also observe sometimes a spark when I plug in to the outlet as well as some wear on the pins because of this. Furthermore in case someone (like me) buys a Macbook in ths US and is in need for a European extension cable (earthed) Apple does not sell a separate one and you have to find it on Ebay or other eshops.

  6. Reply j Feb 4, 2015 2:16 am

    Hi, came across your article. Some of the images are not loading, could you fix it? I have this same issue with my new mbp UK plugs and it is super annoying. The static/hum is too strong to use the laptop and I know the design is crap. How is your experience so far? Any issues? Stable? Will there be any damage to the laptop or user? =)

    • Reply gareth Feb 22, 2015 4:52 am

      I haven’t had any issues, and there shouldn’t be any considering that the longer power cables (rather than just the interchangeable adapter part) already have earth connected. There are some theoretical differences due to the cable length but in practice these are swamped by the need to avoid being shocked etc. I’ll check out what’s happening with the images, I moved servers so may have broken something, thanks for letting me know :)

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