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AC66U 2.4ghz band suddenly crawling

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rmb43

Occasional Visitor
I've owned the Asus AC66U router for a couple years now, running John's fork 374.43 V17E5. Have had no issues other than the random reboots (which seems to be common for these routers).

Now, we recently moved back from Germany (where the router was purchased). After moving into our new house and getting internet setup with the ISP, we bought a cheap TP Link Router to hold us over until the Asus showed up in our household goods shipment. The TP Link worked great and gave consistent speeds throughout the house on 2.4ghz. We have 100/10 internet and the TP Link was showing 40-80 mbps speeds depending on which room you were in. Perfectly acceptable, but I figured the Asus would easily out perform it.

Well, our shipment arrived yesterday and I quickly hooked up the Asus. I first had trouble establishing the internet connection (because I forgot to turn off the IPTV settings that were required for our internet in Germany) but once I sorted that, it was working great for a couple hours. Getting consistently higher speeds than the TP Link throughout the house at about 55-95 mbps depending on the room.

However, by the end of the day something had gone wrong and the 2.4ghz band is now crawling at roughly 1-4 mbps but never going above 5. This has been tested on speedtest.net as well as the ISP's speed tester. This is consistent on several devices (phone, laptop, and PC). If I connect to 5 ghz, I can be in ANY room and it will show roughly 100 mbps every single time.

Things I have tried:
-using different channels (1,6,11, auto)
- switching between 20, 20/40, and auto
-NAT acceleration on/off
-tried different combinations wireless modes (N Only, Legacy, Auto)
-Toggling "Optimize for Xbox"
-Factory Reset using the reset button
-Disconnecting every client except for one (trying to determine if a specific client was slowing down the entire band)
-Flashing latest firmware from Asus' website followed by another factory reset

It seems like something is limiting the link speed on the 2.4ghz band to 5.5mbps but I can't figure it out. QoS is turned off as well. There are several wifi networks visible in the neighborhood, BUT I can hook up the TP Link router and get the normal 2.4ghz speeds I was seeing before, so it doesn't seem related to congestion or interference.

Is this a sign of a dying 2.4ghz radio? Or is there anything else I should try?

EDIT: I have attached a photo showing a TX rate of 5mbps on all of the clients connected to the 2.4ghz band.
 

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Just flashed the latest stock firmware, and reset the router again. Didn't help at all unfortunately. Clients on the 2.4ghz band are still all connecting at 5.5 mbps, no matter how close they are to the router.
 
try changing wireless mode to n-only.
Use wifi analyzer on phone or Acrylic Wifi on PC to see channel usage of other networks in 2G.

Had this due to interferences whan one router got 1+5 and other 9+13 what should be fine, but not in real live as it seems for me they have bad filters with too broad shoulders in 2G.
Or filters are made for DSSS modulation to be compatible with b-mode >20MHz where they need broader spectrum while OFDM (g-/n-mode) could have much nearer spectrum of ~16MHz.
Nobody uses b-mode, but limits of old standard still limits our lifes!!!
 
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Thanks, I tried "N only" as well with no luck.

The fact that it was working great for the first few hours after hooking it up AND my other router works fine on the 2.4ghz band makes it seem like it's related to something other than interference.

The only thing that changed between the time it worked and time it didn't work was that I setup my Xbox One and PC (both of which are not new to this router). But I have tried disconnecting both of those devices from the network and rebooting the router to see if one of them was causing an issue but that didn't seem to be the case.
 
have you done a factory reset? with WPS button pressed while powering on and release 20s later when LEDs blinking slowly

And a firmware update may help too!
 
Yes, ive done both. I did a factory reset by pressing the reset button for 5 seconds. That was one of the first things I tried but it didn't help.

Next thing I tried was flashing the latest stock firmware (was using John's fork up until that point) followed by another factory reset. I thought if anything would fix it, that would be it but I was wrong.

I'll do some more tests tomorrow but at this point I'm not sure what else to check.
 
Yes, ive done both. I did a factory reset by pressing the reset button for 5 seconds. That was one of the first things I tried but it didn't help.

Next thing I tried was flashing the latest stock firmware (was using John's fork up until that point) followed by another factory reset. I thought if anything would fix it, that would be it but I was wrong.

I'll do some more tests tomorrow but at this point I'm not sure what else to check.
Change from Johns fork to stock or Merlin or back would require loading firmware with Asus restauration tool or Mini-Web upload to avoid troubles and factory reset behind with 5s power cycle.
 
According to the readme file included with Johns fork "You can revert back to an original Asus firmware at any time just by flashing a firmware downloaded from Asus's website". I didn't have any trouble doing exactly that. Is there something else I am missing?
 
I see you dont or didnt have troubles, so what, use your perfectly running router ...
Only wanted to help sort out things with possible workarounds.
 
No need to get snippy. I was genuinely asking if there was something I wasn't aware of, like perhaps documented issues when going from Merlin/John's fork back to stock firmware without using the restoration tool? I was only stating that flashing the stock firmware without the tool appears to have been successful (albeit it didn't solve my issue) so we can cross that off the list of things to try.
 

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