SD card corrupted by Etcher & subsequent boot in non-UEFI bios

I started with a 64Gb Verbatim SDXC which always worked okay (as a non-booted disk) in my Sony VAIO. Etcher 1.4.4 indicated success at flashing a 1.76Gb disk ISO (Linux Mint 19 xcfe install/live DVD) onto said SD card.

Then I went into the VIAO BIOS and enabled ‘external drive’ as a boot device. Reboot yielded black screen with top left blinking underline. I waited a few minutes before re-entering BIOS & restoring to HDD (Windows) boot.

Now, the 64Gb SDXC shows as 2.25Mb. I can re-format it, device manager says ‘device is working okay’. I tried putting it into my Camera, but it just says ‘SD Card Error’ or some such.

Funny(?) though, I ran Etcher again, and when I select the drive it reports it as 62.56Gb. I re-etched the same ISO file, Etcher ran again with no errors, but Windows 7 64 bit still says a capacity of 2.25Mb.

Is there any way to recover the full capacity of the SDXC card? Probably I should give up trying to boot UEFI on this PC; I was not sure if it would work but I figured it couldn’t break anything. Obviously I was wrong and lucky I didn’t brick the whole damned PC.

In the old says, there were DOS diskettes one could boot which would then boot from a CD if the BIOS could not do so directly. Is there perhaps something similar to that which can boot UEFI devices from within a running Windows sytem? (I suspect the VAIO bios more than Etcher of corrupting the SD card.)

FWIW, I recovered the stick by burning the ISO to a DVD, booting it (ugh, slow…), opening a command terminal window, then:

$ sudo su

sfdisk -l (then looking at the output to determine the block device)

dd if=/dev/zero of=/dev/mmcblk1 ibs=1M obs=1M

It took a while. I’m not sure really how long because I left it running while I ran some errands and there was apparently a power fail in my house during my absence (TV off, oven clock flashing 12:00, Linux Mint in the shutdown screen, etc.).

But apparently the MBR had been flushed okay. I suspect my BIOS as I said in the original post had put a volume type identifying it as a floppy diskette when I attempted to boot it. After re-booting Windows this time, it saw an unformatted 58.2Gb drive. It is formatting now as I write this follow-up.

When done, I will re-boot the DVD and tell Linux mint to install to the stick. Hopefully it will give me the choice of BIOS vs. UEFI. Perhaps that is a function you can add to Etcher.