How to downgrade your AirPort device's firmware
Reader Glen Green had some difficulty with a solution I recently offered. He writes:
In your recent article “Troubleshooting a ‘Busy’ Time Machine Backup” you discussed upgrading an AirPort Time Capsule’s firmware. I decided to follow these instructions and discovered that my Time Capsule was running firmware version 7.5.2 so promptly updated. Now the front light just keeps flashing yellow and in the Airport Utility under Status, it says “No DNS Servers.” What do I do now?
The first thing to try is resetting your network. To do that you’d follow the steps I outlined in that article. First, power down your broadband modem as well as the Time Capsule. Then plug in the modem until all the correct lights appear. And finally plug in the Time Capsule. When it fully boots it should get the proper information from the modem.
If not you could try resetting the modem—they generally have a Reset button on the back or bottom. The modem, once restarted, will look back to your ISP to pick up the proper settings and then relay them to your Time Capsule. (Check with your ISP before doing this, however, as some have more complicated procedures for resetting their modems.)
Or—and this is really the point of this article—go back to the version you were using before. If I understand your situation correctly, the firmware you previously had on your Time Capsule worked perfectly well. It might again, and thus solve the problem.
Unlike with iOS devices where you’re stuck when you upgrade the device’s software, you can roll back the firmware on AirPort devices. And there are two ways to go about it.
On your Mac, launch AirPort Utility. In the window that appears select your Time Capsule. Hold down the Option key and click on the version number entry. When you do a menu appears that lists previous firmware versions. Choose the one that worked for you (in your case, 7.5.2). You’ll be asked to confirm that you want to do this by clicking a Continue button. Do that and your Time Capsule’s firmware will be downgraded (and, I hope, solve your problem).
You can also roll back firmware on AirPort devices from within the iOS version of AirPort Utility. Just download AirPort Utility to your device, launch it, tap your Time Capsule, tap Version, and then tap Older Versions (see image at the top of the page). Tap on the one you wish to use and—just like with AirPort Utility on your Mac—your Time Capsule’s firmware goes back in time.