If the conventional method of copying to card doesn't work [because the unit's not booting far enough], there is another method using a modified boot bin flashed via updater.exe as an rgn file to execute the txt file. It's a little more complicated that the method in Post #22 as it requires a hex editor to replace a specific string in the boot.bin file. The patching and flashing methods are described in Post #33 here: [Only registered and activated users can see links. ]. Try that if the sd pack in 22 above doesn't work.

PS: I've intentially bricked a 1390 by loading a TTS3 voice to it as the only vpm file. Result endless boot loop and unable to read from or write to microSD by usual method of using ldr.bin with update.txt file in 0972 folder. Removed ldr.bin, patched it, saved it as an .rgn and flashed it to the nuvi with the card inserted. Result, backup_41.bin on card and success shown in update log:
Code:
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Changed update.txt to 'copy,0:/.System/Voice/English_Australian_Karen.vpm,1:/Backup/English_Australian_Karen.vpm' flashed the boot rgn again and my miscreant Voice, the incompatible 1390-bricking TTS3 file, was in the Backup folder on the card. So you maybe can at least backup your files too, even if you can't save the nuvi.

Another flash to delete the voice file [del,0:/Voice/English_Australian_Karen.vpm] then the nuvi was accessible to rename my original voices file folder Poice back to to Voice and it boots up and works fine. Flashed the full original v6.20 fw again. You may have to delete the nuvi's entire directory unless you know what may have bricked it, i.e. a map or other file which was recently loaded.

PPS: Full credit to kunix for this, as i'd actually forgotten about it.