Managed to solve this after a lot of trial and error.....
I did not think that pre-bott mode was working but I discovered that I could actually perform firmware updates with update.exe desipte the fact that the pre-boot mode kept cutting off the USB!
- Downloaded previous version of firmware from Garmin website (5.30)
- Dumped this into RGN tool and checed Hardware ID (in my case 0972) matched the one from GarminDevice.xml from a backup of the unit I made when I got it (this is VERY useful thing to do!)
- I saved this as rgd then used XVI32 to initially invalidate all file extensions and programmed this to the unit but I still could not get it working as a USB device
I then did a bit more reading and found
- Did a bit more reading and found [Only registered and activated users can see links. ]
- I then created a script file in notepad which was a combination of the example script from the above link plus also the additional changes to get round the issue of USB not being seen on the PC. All cudos to the posters of this info but here it is in combined form
REPLACEALL 30 00 30 00 36 00 42 00 BY 30 00 30 00 42 00 36 00
REPLACEALL 00 00 42 00 30 00 BY 00 00 30 00 42 00
REPLACEALL 67 00 6D 00 61 00 70 00 BY 6D 00 67 00 61 00 70 00
REPLACEALL 30 00 3A 00 2F BY 00 00 3A 00 2F
REPLACEALL 31 00 3A 00 2F BY 00 00 3A 00 2F
REPLACEALL 30 3A 2F BY 00 3A 2F
REPLACEALL 31 3A 2F BY 00 3A 2F
- I then went back to the downloaded firware and dragged this into RGN tool again. This time I only exported the boot.bin and boot_fw.bin sections to the rgn file
- Next, I opened the newly created .rgn in XVI32 and then copied the above scripts into the XViscript window and executed the script.
- Finally, I saved this modified .rgn and programmed it to the unit
- Sucess, I could then talk to the unit via USB!
There were some corrupted files on the unit that were empty but locked.
- I took the bold step of re-formatting the Nuvi USB drive (remember I had a backup of the original firmware) and copied the original firmware back to the unit. CAUTION - This seems to have caused me to loose my maps.... I guess they are hidden files that I did not back up - DOH. I have new maps on SD card anyway but pls don't do what I did and format your USB drive without ensuring you have the maps backed up
- Next, I took the firmware that I downloaded form garmin, converted it to .rgn and programmed this into the Nuvi via update.exe
- I then ran webupdate and updated the unit to the latest firmware.
- Finally, turned the unit off, removed the USB cable and re-booted.
SUCCESS - Unit is now working and I will NEVER use the "my dashboard" update again!
Thanks to all who provided various snippets on info on this website! Hopefully this may be useful for someone!