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What to do when can't format a Micro SDXC card on Mac?

I am trying to format a SanDisk Ultra 64GB micros SDXC card using an adapter with my 2015 iMac running 10.12 The card will be used in an Android tablet and it was previously formatted inside the tablet, however, it was formatted in someway that it will not allow me to copy media to it, so I am trying to re-format it on the Mac. Using Disk Utility, I tried all of the different options in the formatting drop-down menu and receive the same error message that it failed when clicking on details it states: Unmounting disk Couldn't modify partition map. Operation failed… Does anyone have any ideas about what I can do? Thanks.

Best Answered by

iBoysoft author Anna Yuan

Anna Yuan

Answered on Thursday, March 9, 2023

The error prompt showing "Couldn't modify partition map." may appear when you are formatting the external drive, USB flash drive, SD card, etc in Mac's Disk Utility app. Generally, the common reason for an SD card showing the "Couldn't modify partition map" error on Mac is that it is physically locked. Therefore, check if the physical SDXC card lock is toggled down to protect it from being written first.

Basically, you can find the physical write protection switch on all standard SD cards. The same applies to your SD card reader or adapter. To disable the write protection on your micro SDXC card or SD card adapter, do the following:

Step 1. Find the lock button on the SD card adapter that is inserted by your micro SDXC card.

Step 2. To disable the SD card write protection, slide the SD card lock up to the unlock position.

Step 3. Connect the micro SD card reader to your Mac. Try to format the SD card on Mac now.

Please be noted that if you haven't backed up the important files on this SanDisk SDXC card, back up them first before formatting. If you still can't write to your SDXC card, you'd better go to the SD card manufacturer for professional help since it may suffer some physical damage.


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