If you recive message that no update available for your unit then this mean that you have MTK chipset.
Here is for MTK:
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p.s.
click Like button and you will see link.You have all that you need in this pack.
I dont know if you know procedure for repair but here it is:
First flash with what is inside folder cure
When you in mass storage create backup of your nuvi if you dont have it (dont forget on hidden .System folder)
Format your device to FAT32
Add back your files from backup but dont add maps (gmapsupp.img,gmapbmap.img,etc)
Flash with what is inside folder original if all go ok your nuvi now work.
You can add back gmapbmap.img,gmapsupp.img etc.