I’m sharing this as a historical record for myself and to help anyone facing the nebulous wifi connectivity issues that have irritated Macbook Pro owners for several years.
The short summary of the problem is that since I bought my MBP last year, the wifi has been spotty. With Lion, anything with internet connectivity would fail to load, and I would restart the router to get back online. After I upgraded to Mountain Lion, anything with internet connectivity would stop responding entirely. Force quitting failed, and even Terminal became useless, forcing a hard restart of the entire machine. Bad news.
After an archive and install last week, which rewrote all the OS and system files, my wifi cleared up nicely. I ran without issue until I connected my external display. Almost immediately after that, the wifi failed, leading me to suspect something with the Thunderbolt port was interfering with the wifi receiver.
Certain external monitors and LCD displays: Certain displays may emit harmonic interference, especially in the 2.4GHz band between channels 11 and 14. This interference may be at its worst if you have a portable computer with the lid closed and an external monitor connected to it. Try changing your access point to use 5 Ghz or a lower 2.4 GHz channel.
Several people reported success from setting their router’s 2.4 GHz channel to a lower number and from switching to the 5.0 GHz band on a dual-band router.
In the past, I’ve had little success staying connected to my router’s 5.0 GHz band, due to its weak strength in my office, but that was with my old Netgear router. Since then, I’ve ponied up for the more expense, less-featured Airport Extreme, hoping that alone would fix my wifi problem. I hadn’t bothered to use the 5.0 GHz band, given my past experience, but faced with the effort of a clean install of OS X, the last resort, I gave it a go.
I decided to try this first, before manually lowering the 2.4 GHz channel, and it worked really well, getting full down/upload speeds, at least when disconnected from the external display.
When I connected the display however, the bandwidth fell by 75%. On a hunch, I turned the laptop 45 degrees to match the angle it had before I connected it to the display, and voila, full bandwidth returned.
I’ve had steady connectivity since then, and the bandwidth speeds have stayed high.
After trying so many things, it’s difficult to identify the root cause or the string of fixes that resolved the issue, fingers crossed. What’s odd is that neither Apple Care nor the Genius Bar asked about an external display, which seems to be a contributing factor. I’m not blaming them, just saying.
Assuming this finally closes the book, the lesson learned here is an old one. This stuff is difficult.
Anyway, if you have this same wifi connectivity issue with your MBP, I hope these tips help.
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Update: Turns out it’s not fixed. Wifi locked up again, requiring a hard restart. Annoying. Maybe one bright spot, the frequency of these occurrences may be lower now, every few days vs. several times a day. We’ll see. Unfortunately, I’m looking at a clean install of OS X as the next step, before I beg Apple for a replacement machine.