I had exactly the same problems with all my alu iMac's 27" since 2009, and finally i solved the problem
I got the problem on all ver. of snowleopard and Lion.
Now im running OS X Lion 10.7.4
1. WiFi suddenly drops with no reason
2. WiFi drops when timecapsule start backing up
3. WiFi drops right after wake up from sleep mode (more than 15 min.)
Only thing to do is restarting computer before i got my WiFi back!
After serval days in cooperation with a apple techinal engineer, i found the solution.
1. Go to PREFERENCES / ENERGY SAVER / COMPUTER SLEEP
2. Set the parameter "computer sleep" to anything you like EXCEPT of 15 min.
(If you set "computer sleep" back to 15 min. the problem returns)
I have spend serval months on this problem and tried everything from:
making new account
power supply reset
clear all network locations
You name it...
No matter what i did, it was only my imac who lost WiFi connection.
My iPhone and Macbook have been connected all the time without problems.
Hope it works for all of you?
Please let me know?
Message was edited by: Thomazb
Okay after almost 2 months of testing (and receiving a call from Apple Support offering to help) here are the things I have observed:
1) Assigning a dedicated channel for my Wifi network (through Airport Utility) did not help with the problem. In fact it took mere minutes after I restarted my iMac to experience another connection drop!
2) Assigning a separate SSIDs for the 2.4GHz and 5Ghz channels (e.g. "blah" and "blah 5Ghz") and connecting to only one of the SSIDs does help with the WiFi dropout. I tested with the 2.4GHz SSID for 2 weeks and another 2 weeks on the 5GHz and I have not experienced a WiFi dropout that required a computer restart to fix.
3) However using approach (2) above the WiFi connection would suddenly slow down to a grinding halt while doing something network-related (e.g. Time Machine backup, Diablo III, YouTube, Facebook etc), and would resume after up to half a minute or so. Didn't need to restart the iMac during this connection slowdown though.
Based on the above observations my theory is that (a) the network code for switching between 2.4GHz and 5GHz channels under the same SSID is buggy under 10.7.4 and (b) the WiFi connection would sometimes slow down to a halt that the OS is able to recover from.
Let's hope that they fix this in Mountain Lion and (hopefully) in 10.7.5...
I'm 4 years into Apple/OSX. Until Lion it's been a very good experience. The Lion wifi experience reminds me a lot of Windows and the reasons that I left a Windows environment. It seems Apple wasn't thing clean or easy with Lion. It seemed to be thinking the more wholesale changes the better -- just make everything different. The notion a pad and desktop that have similar looks and feels makes liittle sense. I suggest Apple rethink the Lion direction and take another look at Snow Leopard.
FYI, we have been experiecing the same issues for quite some time. I kept attributing it to the Mindstormes online game my kids are always playing, but as this has continued to keep happening, I have finally begun to search the Support posts to see what I could find. So glad I came across this.
Model: Late 2009 27" iMac
Problem: Drops WiFi & Ethernet
Upon turning off computer, rebooting, then rebooting our DSL (ATT&T) sometimes it will recognize our WiFi/Ethernet, but mostly it will not. Currently, NOT Working again.
Also, when we try to click on the Network Connecting, it just spins and freezes, never allowing me to click on anything to make any changes. I never realized these problems coincided with the 10.7.4 update.
We have several other Apple prodects in the house which also use the DSL, they never have had an issue, including out 2006 iMac. This has strictly been a probem with the newer iMac so I new it was not a DSL related issue. In the past with I've had trouble with an iPod connectig to WiFi, I did give it a static address and that solved the issue.
From reading these posts, it sounds like channel changing or dedicating a static address or going backwords onthe OSX update may be temporary fixes unitl ML or 10.7.5 comes out? Before I finished reading all of these posts, I went ahead and began redownloading OSX Lion, only have another 1/2 or so to wait and see if it's a temp. fix for us.
This has been such a time waste and irritation!
Thanks all for posting your comments that may help others!
Well, before I installed Lion 10.7.4, my imac wifi was perfect. After I installed Lion 10.7.4 package, I turned on my Imac 2011 and it didnt connect to my wifi signal. Wifi is ON, but not connect to my wifi signal automatically. I reinstall many times old version 10.7.3 but now I have the same problem.
My conclusion is that something on OS Lion is not working fine, because I have installed Windows 7 on my Imac too, and never I have problem with wifi signal, never lost my signal, and after sleep work perfect!. On OS Lion after 5 Sleeps mode, 4 didnt get wifi signal and 1 worked.
So, I hope Apple could found a solution for this problem, please.
Have a nice day.