[FS#1248] On Asus RT N56U changing the wifi channel for 5ghz from anything but auto prevents wifi from working

[LEDE Bugs]

The following task has a new comment added:

FS#1248 - On Asus RT N56U changing the wifi channel for 5ghz from anything but auto prevents wifi from working
User who did this - tomas muehlhoff (targa)

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I do have 2 RT-N56U Units, so far I never used 5GHz, so this didn't appear to me. Now that my neighbors decided to really fill up all 2.4GHz channels I wanted to try 5G, with no luck. It came up eventually, but now it doesn't. Tried all of the above hints. (LEDE 17.01.4 r3560-79f57e422d)

"Reading the Internet" it seems obvious that this is not necessarily a LEDE problem, but problems arise with Asus FW as well.

I was reading on Padavan release notes and he states that he did some backporting and in the forums it says that 5GHz problems (which are still in ASUS fw and WERE in Padavan FW) are fixed now.

Release notes say: 3.X.3.6-069:
​https://rt-n56u.soulblader.com/files/README

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    Fixed broken 5GHz TxPower adjust w/o clients connected (backport from 2.6.x.x driver). 

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Latest FW bins are stored here:
​https://bitbucket.org/padavan/rt-n56u/src/dff9a3421d1da8f6678829a05fb7131997b51e67/trunk/vendors/Ralink/RT3883/?at=master

I tried to replace the firmware binaries, but obviously it requires a Lede Image build which is a bit time consuming if you don't do that regularly.
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More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=1248#comment4063