Microsoft Provides Windows 10 Technical Preview Fix For Lumia 520, 521 Smartphones (Updated)

Last week, reports began to surface that the latest build of Windows 10 for phones was bricking Nokia Lumia 520, 525 and 526 devices. The failure reared its head when users were trying to roll their phone back to Windows Phone 8.1 by using the Windows Phone Recovery Tool. Microsoft halted the Windows 10 rollout for those specific models and began a thorough investigation of the issue.

On Monday, Microsoft provided an update focused on the Nokia Lumia 520 and 521 devices. The company said that users experiencing problems either see a red Nokia logo or the phone has a black screen and can no longer reboot. For those who have a bricked device, the company said it's still investigating the problem.

The company provided a few tips for customers facing the red logo. First, you can grab the latest Windows Phone Recovery Tool (1.2.4) by closing the tool and re-opening it. Also make sure the phone has a good power source and then re-flash the phone once the new tool is installed. If you see an error stating that the device was not detected, you're encouraged to proceed anyway.

Customers with a black or blank screen are encouraged to follow these steps as well. However, these affected devices are "in a different state" and will take longer to recover, if they're even recoverable at all.

So what is happening on Lumia 520 and 521 devices? The good news is that only a small portion of these Lumia phones are having issues.

"It was discovered that some devices are having trouble accepting the recovery image data being flashed," Microsoft's update said. "The blocks of data were too large for some devices to handle, and the memory on the device was having trouble with the speed at which the data was being written. In short, devices were getting too much data, too quickly. This would cause the failure as the new software is corrupted."

To fix the issue, Microsoft has reduced both the size of the data blocks and the data writing speed so that the phones deal with smaller chunks of data at a slower rate. This "fix" will be added to a new version of the Windows Phone Recovery Tool, which is now a mandatory install. To get this update, close and re-launch the Recovery Tool; the client will automatically offer the latest build.

Microsoft's report added that the company plans to contact users with the Lumia problems in order to perform "additional real-world testing." If these phones show great results, the company will turn the Windows 10 update back on for all Lumia 520 and 521 phones. The update didn't say anything about the Nokia Lumia 525 and 526 devices, which are also seeing recovery errors.

If you want to get into the Windows Insiders Program and test Windows 10 for phones, you can peek at the list of supported phones here. Potential testers can download the Windows Insider app here. Testers must also be a member of the Windows Insider Program in order to update to the technical preview build.

Update, 4/20/15, 12:40pm PT: Microsoft Insider's Gabriel Aul confirmed via Twitter that Microsoft has paused the distribution of Windows 10 Technical Preview for the Lumia 52x series. He said the problem has been resolved and the company will resume offering Windows 10 Technical Preview to the Lumia 52x line late April 21 (tomorrow).

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