Like many people I was desperate to update my Noikia Lumia 7.5 to 7.8. I kept reading all gadget websites everyday to see if ATT would send out the update. Some sites suggested using an update software by an enthusiast but it came with several warnings, so I decided not to go that route. I my quest for other information, I bumped into this forum which talked about some weird Zune bug to force an update. This seemed much safer to me as it was still Zune which was doing your update. So I tried it. I am glad to report that it works great!
1. Disable Wifi and Cellular Data
2. Connect to PC, open zune, settings, then phone, then update. It won’t find any, but you NEED to do this.
3. Change the tab (navigate away from Update). Now click on Update again, but disconnect your internet connection after 2 seconds. BAM an Update is available after waiting a few seconds!
4. Hook up internet and proceed!
1. I had a tough time doing STEP 3. You had to be really quick to disconnect the internet after you hit UPDATE. I dragged Zune to my lower right corner, so that my mouse has lesser distance to travel. I guess if there is a Keyboard shortcut to disconnect the internet, it would be advisable.
2. I also had to do this whole thing twice. I think first update just preps it and second actually does the 7.8 update.