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

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.

Just found out about that problem. The only solution now is Channel 1. Apple Support guy said that it should be fixed with Yosemite. Thanks for your help guys.

I am having the same issue with Yosemite, but so far changing the control channel on my 5G router to 149 as suggested in an earlier post is working.

I had this issue with a new MBP retina. I have two external Dell monitors hooked up to adapters that go to their DVI-D connectors. Each adapter takes up a Thunderbolt and a USB port, so it maxes them out. Having the adapters plugged into the MBP dropped the wifi by x10. I solved this by reading this thread: Macbook pro retina drops wifi when usb 3.0 stick connected

I moved the cables and the adapters as far away from the back hinge as I could. They had been about 4" away. The wifi went up to almost the same strength and throughput as when the adapters were not plugged in. Hope this helps.

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?

Try this, go to system preferences then network preferences. Select Thunderbolt Ethernet and "make service inactive" (click sprocket icon at the bottom)

This improved my WiFi connection speed. My thought being that Thunderbolt is a multipurpose port also used for ethernet and may be taking priority when it is plugged into any device. If you are using WiFi Thunderbolt ethernet is obviously not needed.

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.

This same problem appeared for me after months of using the exact same hardware and software setup (MacBook Pro 10,1 + Yosemite + 3rd part Thunderbolt display adapter + Dell monitor).

After trying 5 or 6 suggested fixes, I found that disabling my AirPort Express's AirPlay feature fixed the problem. Obviously this makes it hard to use AirPlay :-(

rodsab wrote:

Try this, go to system preferences then network preferences. Select Thunderbolt Ethernet and "make service inactive" (click sprocket icon at the bottom)

This improved my WiFi connection speed. My thought being that Thunderbolt is a multipurpose port also used for ethernet and may be taking priority when it is plugged into any device. If you are using WiFi Thunderbolt ethernet is obviously not needed.

This tripled my speed on WiFi with a displayport monitor connected. I did not have this issue previously, but today I was using a different cable and my WiFi would not connect at all. After some troubleshooting I discovered that it was only when my 4K Dell displayport monitor was connected. I switched to a different cable where I could negotiate a WiFi connection, but my transfer speeds were about 1/3 of my actual bandwidth with heavy packet loss. After making the Thunderbolt Ethernet service inactive I ran another speed test and had full bandwidth available with no packet loss. This is a pretty messed up problem, Apple. I'm on a 2014 MacBook Pro maxed out running Yosemite 10.10.4.

Thank you for posting this… it worked for me!! 🙂