Cannot Update 802.11ac BIOS

Any ideas of what to try next short of resetting the entire device?

Reset is likely necessary but there is no need to lose your current setup.. Go to the TC and simply export its configuration.. do the factory reset and then import it again.

Plug the TC directly to the modem by ethernet if it isn't already..

Do the very simplest setup you can and then try again.

7.7.1 has the security weakness.. and that is the main reason Apple wants you to update it.. it is not actually a huge update otherwise but once you go to 7.7.3 you cannot go backwards.

Do you have an apple store nearby where you could book a genius appointment and take it in and let them do the update for you.. or see if the issue is the TC itself.

Something is wrong for it not to be able to update.. I do not trust the Yosemite version airport utility at all, but the iOS version should work ok.

Is there something unusual happening.. ie you bought the TC overseas and trying to flash it from the wrong server.

Apple has made firmware upgrades automated but once you download the firmware to a computer it is stored there.. So if you know anyone who has an AC version TC that has been upgraded.. ask them to upgrade yours.. and it can use the upgrade firmware they have already stored.. in

~/Library/Application Support/Apple/AirPort/Firmware

Check what is available because it might give you the download location of the file.

http://reverseengineering.stackexchange.com/questions/3371/reversing-apple-airpo rt-express-firmware-updates

This shows you the structure of the file that helps the airport download the correct firmware.

There is a bit here. .on manually downloading the firmware.. take great care with this sort of thing.

Where I can find AirPort Base Station Firmware Update 7.7.3

I bought the unit from Apple (US) but I don't have a Apple store within 50 miles of me unfortunately. The next time I will be near one, I'll pack the unit up and take it with me.

They were never made for manually downloading and upgrading.. but I wanted you to try that to ensure you could actually access the download firmware store.

The US one should be ME177LL/A

This model is 119 in the database.. and so the firmware should be 7,883,160 bytes

Make sure you don't have the firmware for the Airport Extreme AC model. which is slightly smaller.. and is 120 in the database.

Anyway.. important thing to notice is that firmware update is almost purely to fix the security issue. And although it is a major bug from the point of view of most end users.. a hacker would need to already be in your network to take advantage of it.. ie your security has already failed.

So I would not be over concerned unless you are using unsafe network practices.

I never know how much I can get away with here.. I guess since other people have posted it I can ..

http://apsu.apple.com/data/119/031-01135.20140418.Lfrf4/7.7.3.basebinary

My post might get deleted..

There should be a file called version.xml in your directory as I showed above.. where exactly it will be I am not sure but if it isn't there, maybe that is part of the trouble.

Does the user you have logged in have full admin rights? If not please try using a full admin user?

My email is in my profile.. so if you want to talk to me direct that is fine.

My replacement AC version TC should turn up today and I can test it some more.. but it was already at the latest firmware.. or at least the first one I bought was.. maybe this one will need an update.

Ok.. well done.

I wonder if Yosemite version of the airport utility is the issue... version.xml has been there for ages.. as I have used it in the past.. well since Snow Leopard when I got into Macs.

There is a couple of major bugs in Yosemite.. have a go at exporting and importing the configuration file of the TC. According to some people posting it crashes the utility so something is far from good there.