Wifi/ethernet works only for a short time then crashes?

[James Whitehouse]

Hi, I have a strange problem with my iMac's connection to wifi internet (as well as the ethernet when cabled direct to the modem).
I am experiencing the same pattern each time. My iMac (late 2012) connects well to the internet (>10mbps) for a short time after being switched on. However, a few minutes, maybe 20 minutes max thereafter, the connection slows to an almost frozen state with barely any connection (<1mbps). The problem can be solved either by me (a) switching off my iMac and restarting; OR (b) switching off my modem and re-booting it (leaving iMac on). However, the problem then repeats and after a few minutes I'm back to square one.
I thought it must be the ISP or a line fault, because when I experience the freeze it applies to all my devices (iPhone, iPad, MacBook Air) as well. However, after numerous tests my ISP confirms that the stream to my flat is good and there is no fault. Since the fault is corrected when I shut down my iMac and restart it (and the problem is then immediately corrected for all other devices too), I'm wondering is there a system problem within the mac itself which is causing this?
It's weird as for the last four years I haven't really had a problem with the internet, and certainly never experienced this before.
My software (OS X 10.9.1) is all up to date and I don't have an Airport. Connecting via ethernet or wifi seems to make no difference.
Anyone got any ideas?

 

[oldscribe]

Hi,

As a simple test take your MBA or iPad out to a public WiFi and test the connection continuity. As I suspect this is defiantly an ISP or Modem hardware issue.

1) Make sure your modem software is up to date.
2) Also you could try deleting the network setting and reinstalling.
In the Preference Pane, try deleting it ("-"), hit the Apply Button, then Add it back ("+"), and Apply

 

[James Whitehouse]

Hey oldscribe,

Thanks for the advice! Have taken my devices out and have no problem connecting with the portable devices elsewhere, so definitely not them. However, since writing I think I may have zeroed in on the problem, or at least the source of the problem... I think it's my iMac! I noticed today that when I turn my iMac's wifi connection off, but leave the others connected (MBA, iPhone etc), the internet works fine for them for a consistent period. I hadn't noticed this before as my iMac is my main system and the one I principally use, the others being satellites.
So maybe there is something with the iMac's settings which is messing with the whole flat's wifi generally (when it's on), which would explain why it constantly needs a reboot. Is there a suggestion for returning the iMac to its native default wifi/internet settings? Perhaps that will simply clear up the problem.

Thanks!

James

 

[oldscribe]

Hi,

1) Delete home network from the list of preferred networks with the ( - ) in the Network Preferences, click OK, and then click Apply?
2) Check KeyChain Access for the network listing?
Macintosh HD > Applications > Utilities > KeyChain Access
Look for a listing with the network name, click to highlight, then delete the entry.
3) Restart iMac and renter your network settings.