This tip helped me access a broken Win10 hdd that was stuck in readonly mode ..

How to remove 'Read-Only' error from hard drive/USB/SD card/external hard drive?If your storage device such as USB drive, SD card or external hard drive are write-protected now with 'Read Only' mark, don't worry. Here in the below, you'll find an effective method to remove write-protection and get rid of 'Read Only' error from your storage device ... 

Step A. Run CMD to remove 'Read Only' from hard disk/USB/SD card/external hard driveIt's quite simple to remove and fix storage device 'Read Only' error by applying CMD command. 
The only thing that you need to keep in mind is to be very careful while following the CMD guide steps to remove the ”Read Only” error from an SD card, USB drive, hard disk or external hard drive. 

• Connect the ”Read Only” storage device such as an SD card, USB, external hard drive  to your PC
• Open a Command Prompt by typing: command in the Search tab, click Command Prompt
• Type: diskpart and hit Enter
• Type: list disk and hit Enter
• Type: select disk 0 and hit Enter (0 will be the drive letter of your read-only hard drive/USB/SD card, etc.)
• Type: attributes disk clear readonly and hit Enter
• Type: exit and hit Enter to finish the process

Step B: After this, your storage device will be accessible again and you will be able to read and use the saved data on your SD card, USB or external hard drive. If you still cannot access the saved data on your storage devices or have lost some saved files/documents, don't worry.
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​source: easeus.com/storage-media-recovery/fix-read-only-error-on-hard-drive.html