My wifi drops when I plug in an external monitor through the thunderbolt port

Ok this issue has been driving me insane!

My setup is as follows:

2012 15" rMBP

OSX 10.8.2

External Dell U2410 display (1920 x 1200)

MDP-DVI adapater from Monoprice

DVI to DVI cable connecting to display (3ft long if that matters)

Full size Apple keyboard (wired) connected via USB hub in display

External Apple Magic Trackpad (connected via BT).

I am 99.9% convinced this has nothing to do with the el cheapo Monoprice adapter and here is why:

MBP sleeping with lid closed. Wake by using keyboard. Wifi connects with full signal (according to icon on menu bar - this never changes). speedtest.net shows speeds at 1 - 1.5 Mbps.

Unplug adapter and plug back in immediately so the MBP doesn't sleep.

speedtest.net shows speeds of 15-16Mbps. This is the speed I should be getting and the same speed that I get when not using my external display.

Speed maintains until the next time my MBP goes to sleep. This can be for hours at a time the speed is maintained!

Wake and the same thing happens again. Speeds back to 1 - 1.5Mbps. {aside: It is almost like the speed is being throttled because it is always darn near exactly the same speed when performing poorly.}

Unplug MDP and replug... excellent speeds again.

Note that I can NOT perform this workaround when using the MDP next to the power adapter. This ONLY works with the MDP next to the USB.

The fact that I can get consistent speed after unplugging / plugging back in tells me this has absolutely nothing to do with interference as what many people have discussed. How could it possibly be related to interference when it works fine after unplugging / plugging back in for hours at a time?

This issue has been around for a long time (ie as far back at 2010) and really needs to be addressed by Apple.

this is ridiculous, if I use any other screen resolution than the default the internet works, if I return to default the wifi craps out... how is this happening in 2013 after so many macbook iterations ? my MBA is 8 months old, there were three osx updates... this *****

I agree. I have a late 2011 11" MacBook Air that I am trying to connect to a 23" Cinema HD display. As soon as I do, it kills my wireless. It still shows that I have full bars but I have no speed at all. As soon as I unhook the monitor, wireless opperates as it should.

I am using this in a work environment so making a change to the router channel is not as simple as if I was at home.

Any other help anyone can lend would be great.

I am relatively certain that the WiFi channel has absolutely nothing to do with it.

choots79 you are the first person to mention issues with a Cinema display. I am very surprised to hear that an Apple display doesn't work with the MBP. Unfortunately this lends more evidence to the fact that there are issues with the Thunderbolt port. I have to believe that it is a software issue so here is hoping that Apple actually fixes it.

I thought it was an issue with the mini Display port to DVI adapter I was using so I bought a new one from Apple today and it still does exactly the same thing.

Very disappointed.

It is a Cinema display but, it is an older model the has an DVI connection. I am using the minidisplay port to DVI adaptor. I am using the rocketfish adaptor sold at Besy Buy. I tried one from Monoprice today and that seemed to make a small difference.

I am going to trade out the rocket fish for the apple adaptor tomorrow and see if that makes a difference. I'm also going to talk to the guys in the network operations center and see if they can make a channel change.

I'm trying to use mine in a enterprise environment so changing the channel on the access point is not that easy. I just broke down and bought the USB to ethernet since I have drops at my desk. Obviously works like a champ now.

So far so good!

Changed my router channel to 1 a few days ago and haven't had any issues since!

Not the best situation for people in enterprise environments but it seems to be a solution for me at this point.

I had same issue connecting Early 2011 MBP via off-brand mini-displayport -> HDMI -> DVI on an older model Samsung LCD.

It was working fine, then I was playing with Mac Settings for the Display Resolution. Changed from 'best for display' to 'scaled' and my network dropped off. Changed back to 'best for display' and still didn't come back. But then changed from 75 hertz to 60 hertz and instantly my wifi network works again!

Hope this helps someone else out there...

OK

ready for some real Voodoo?

It seems that changing the display preferences is critical

I have had this set up:

2012 MBA -> Generic Thunberbolt to DVI Adapter -> Apple Cinema Display 23" from 2005

Wireless has been working flawlessly on Channel 11 for weeks, with the lid closed.

A friend came over with his 2012 MBA and I said "hey, take a look at how it looks on a bigger screen"

We plugged it in, had to open display preferences on HIS machine and do arrangement and the like. Didn't actually use the net.

Later that day I plugged in my MBA and .... slow to no wirless.

Wondered about new interference, put in an old Airport Express to boost the signal.

Nothing worked.

Have now changed the channel to 5 and am getting about 10Mbps

Go figure!

I'm one more user experiencing this problem, which was largely solved by switching my router to channel 1.

I've got a mid-2012 MacBook Air with great wifi speeds (50/25 Verizon service testing at those speeds or better) until I plug in my Dell 2007FP 23" monitor through a Apple Thunderbolt to DVI connector. It then drops to 10-20% of those speeds, especially the download rate. Changing the Dell monitor resolution also largely fixes the problem.

BTW even after fixing the problem by using channel 1, when the MB Air lid is open the speeds are 20% higher. Turning off bluetooth also speeds things up incrementally.

Thanks for everyone's posts.

keywords: Verizon FIOS wifi slow MacBook Air Dell external monitor Thunderbolt port

If hooking up a thunderbolt output for a display and your wifi stops working try the following.

If your using an apple airport express go to the finder.

1. Type in airport, then open airport utility.

2. Click on Base Station.

3. Click Edit.

4. Click Wireless.

5. Open Wireless Options tab.

6. Where you see the 2.4GHz Channel listed change it to 4.

7. where you see 5GHz Channel Change it to 149

8. Click save and apply.

That should do the trick.

Hey.. same issue here.. as one user more

Apple should take care of this..

MB Retina 13 late 2012-->2 apple original minidisplay to DVI-d adapters ----> 2 hpLP2465 monitors -->lid close or open.. (for 3 screens)

3 screens working perfect, Internet Access, Total Play 200/50 full access testing, screens 50 cms away from MBP

Change one minidisplay with one DVI-d to HDMI for same display Works great (still 2 monitors, trying to work with three exterrnals.. lately)

Working great 1 week, 1 day broke the wifi, disconnect and reboot anything..

next week working great, 1 day broke again..

i`ve tried changing channels -- works great as solution

after....

Using multicontact for energy for monitors on the same conection.. plus a laptop (VAIO)adapter, we disconnect the laptop adapter--- works great..

So far so good..

Next week I approach a cellular alcatel phone under the monitor and again.. the WIFI presents problems..

Seems that the protection from radiation offered by MBP is deficient.. when many technology devices are near..

Apple should fix this.. as its hardware issue.. should make a repair recall. as many users having this issue..

I had exactly the same issue with MBP Retina 13 and Dell 2408 DVI2mini-display and what helped here was to pull out the dvi-cable completely (as i tried to move away as far as possible from the monitor (aprox. 3 meters) and then moved closer to see what distance might work.) At the end I was 30-40cm away but with straight cable and now WiFi still works having the MBP and the 24" monitor side by side.

I too changed wireless router channel from "Auto" cannel to "1" and back to normal. I had this issue a few months back but it was affected by Bluetooth mouse. I turned off Bluetooth and wi-fi worked. Now it seems to be affected by the wireless channel. Weird stuff. What's next?

I had the same problem with external Dell monitor. I've solved with following:

I've changed display hertz rate from 75 to 60.(System preferences -> Display)

And no problem after that.

Also I dont see the difference between 75 and 60.