I'm having the same problem where my 2.4Ghz signal is on port 64 and the 5Ghz-band-1 is not working. I tried your steps Texas, it did not work for me.

It's nuts that is issue has been around for 3 months with no resolve...

I was able to "fix" this issue (for me) -- it's not a perm solution since I believe the firmware needs correcting -- TP-Link engineers, we're looking at you.

Here is what I did - it's been working fine** so far

1 - Downgrade to firmware: 1.2.0 Build 20170630 rel.49653(5553)
2 - Reset everything to Factory Default
3 - Set everything up as I wanted it (Parental Controls, DHCP server settings, etc etc). Note: 5GHz-band-1 was still disabled. This was painful.
4 - Logged on via the Tether app and configured my 5Ghz-band-1
5 - Hard reboot of the router: I pushed the button in the back, turned it off - then pulled the plug for about 10 seconds.

>>
6 - Don't touch it.
7 - If any settings updates are needed, I will hard-reboot the router after they are set because the 5Ghz-1 signal will disappear ...

Notes**:
- After the router was plugged back in 5ghz-1 signal re-appeared and I was able to connect to it.
- _IF_ I do any settings modification, the 5Ghz-1 signal disappears, and I'm forced to hard-reboot this router to make it re-appear. I disabled the LED control settings to turn them off during certain times, since I _think_ (don't know) if this will cause an issue -- and it's a silly feature imho.
- I don't know if the latest Firmware (the one released in sept) will work with this approach
- All my wireless security settings use TKIP (2.4,5-1,5-2 and 2.4-Guest)
- This device is being RMA'd, so I have no intentions to upgrade firmware.
- I wasn't able to downgrade the firmware any further back ...

thanks for your input and the "fix", digitalintruder! Unfortunately, it didn't work. Doing so, I was about to get 2.4 and 5-1 connected to a channel again but it won't Broadcast. The replacement will be RMA'd. Will be sending both unit back this week. no more upgrading the firmware this time around. Good luck!

JaysTPLINK wrote

thanks for your input and the "fix", digitalintruder! Unfortunately, it didn't work. Doing so, I was about to get 2.4 and 5-1 connected to a channel again but it won't Broadcast. The replacement will be RMA'd. Will be sending both unit back this week. no more upgrading the firmware this time around. Good luck!

Sorry to hear that - after my 'fix' my wife/daughter who connected to the 2.4GHz said it was incredibly slow - so I ran a speed test - less than 20K up/down speeds ... I'm in the process of RMAing this device too -- I still think it's a firmware issue ...

digitalintruder wrote

Sorry to hear that - after my 'fix' my wife/daughter who connected to the 2.4GHz said it was incredibly slow - so I ran a speed test - less than 20K up/down speeds ... I'm in the process of RMAing this device too -- I still think it's a firmware issue ...

The question is why can't TP-LINK programmers release a firmware that works? I am on 1.0.9 Build 20170406 rel.53986 and refuse to upgrade beyond that. Mine unit works fine and no need to go through the drama of installing buggy software.

Ok,.. about 3 weeks of operating perfectly I have lost the 2.4GHz radio. This HAS to be a hardware issue. Firmware can't magically just change things like this.

I RMA'd two C5400 routers and the last one has been stable for around eight weeks. Firmware version 1.2.2 build 20170912, rel 56240.

That's good to hear. I ended up RMA'ing the one that seemed to break - then upgraded to 1.2.0 Build 20170630 rel.49653(5553) (without skipping any versions in between -- and following the directions of each upgrade to the letter). It's working like a champ so far - but I'm worried about the version you upgraded to. Any special steps - or did you just upgrade to the lastest version as soon as you got it?

One of the odd things, I'm not sure how to repro it - but after I setup the RMA'd unit (thankfully it was brand new), a popup happened while I was browsing asking me to upgrade the router -- i dismissed it - I just hope that it requires authentication if someone in my house accepts it...