Thread: Nüvi 3790

One problem that is often experienced with Garmin devices that have been 'cross-flashed' (converted to a different but similar device) is that there can be device-specific data written to it's nonvol memory. In your case you've experimented with 3790 US/EU to both 3790 SG and 3490 EU/US and now an attempted re-conversion to 3790 US/EU.

As to the use of the word "deleting", i try to avoid using it in regard to nonvol because it might be thought to have two quite separate meanings - i.e. clearing or erasing. "Clearing" (*see below) nonvol both before and after flashing fw helps by removing recently written albeit non-essential data which might conflict with its 'new identity' and be poisonous to it. Some deeply corrupting data if not removed by "clearing" might need to be removed by "erasing" ALL data from the nonvol (#again, fully explained below). That could have possible unintended consequences involving other losses, depending on the state of the device at the time.

If there is some corrupting data remaining following cross-flashing which isn't removed by CLEARING non-vol before and after the flash, it's quite possible the device will be fine ... at least for a while and maybe even forever. However even a few bytes of bad data can potentially cause the device to crash and turn off, freeze, spontaneously reboot, boot-loop, or worse, die completely with no reaction to the power button. So not clearing nonvol might have no consequences, or result in a minor inconvenience, or prove fatal... i.e. a "dead" (as in "never-turn-on-again") device.

It's pretty hard to kill a 37x0, most can be resurrected if they aren't "dead" and yours isn't because the backlight still works. Not being able to see the screen is highly inconvenient because of the way it attains preboot, whereas for most device it's easy being the left-hand top corner is the magic spot. Probably you can still attain preboot if you can work out where the "G" in GARMIN would be if you could see it, and so the pics behind the Spoiler below shows is where it is so break out the ruler:

Spoiler: Images

[Only registered and activated users can see links. ]
Of course you now can't be sure whether it thinks it's a 3790 or a 3490 so a short-cut is to use your left thumb and hope that works:

[Only registered and activated users can see links. ]

Another way we might get it going is via SD card text commands if it can still recognise a media card, but let's see if you can get it into preboot first. You can be sure it's in preboot by following this:

• Try to use a Windows desktop PC for this rather than a laptop and plug a 'known-good' USB cable into a rear USB2 port (no hubs and avoid USB3 or front ports)
• Hold the power button down while in a dark place until you're sure the nuvi's fully OFF (no backlight)
• Load the 37x0 RGN file into Updater.exe and select the Radio Button next to "USB Device" (don't use safe-naming, naming it just off.rgn will do then it won't matter whether the device is presently a 34xx or 37xx or half-converted whatever)
• Place the mouse cursor over Updater's "OK" button
• Hold the device in your left hand with your thumb on the screen, fingers behind to firmly hold the device while you plug the cable into its microUSB port (whiuch will power it back on)
• Watch the window next to "USB Device" and immediately you see it populate either click OK or hit your keyboard's Enter key
• Keep holding the screen firmly until Updater shows a message, hopefully it'll be "success" and the device will now be a 37xx again then we can go further to fix it after you've cleared nonvol again.

*Clearing nonvol is done via the hidden memory onboard as you'll already aware and it simply removes any recently written data from the nonvol region.
#Erasing nonvol is a far more radical and risky procedure which involves removing all data from the region and that relies on the device being able to then successfully re-boot during which it re-writes the (now completely empty) nonvol memory region from scratch. If that goes wrong or doesn't happen the device may either be toast or may not perform as designed ever again. If it goes right you'll have a fully working 3790 again. Erasing is done by using the command "ergn" but it's an absolute last resort tactic so don't try it until we've exhausted all other possibilities.

Originally Posted by Neil

If there is some corrupting data remaining following cross-flashing which isn't removed by CLEARING non-vol before and after the flash, it's quite possible the device will be fine ... at least for a while and maybe even forever. However even a few bytes of bad data can potentially cause the device to crash and turn off, freeze, spontaneously reboot, boot-loop, or worse, die completely with no reaction to the power button. So not clearing nonvol might have no consequences, or result in a minor inconvenience, or prove fatal... i.e. a "dead" (as in "never-turn-on-again") device.

Today I took a trip with the route programmed in the nüvi and there was a moment when it turned off and restarted by itself. The curious thing is that it has continued with the planned route it had.

Can this also happen again if I convert it to a 34xx?

Originally Posted by Neil

Try this: Select the Locale/Language then take it outside to get a satellite fix to see if it then goes to normal boot when re-started. It might take a while to get a good fix after a comprehensive re-set even if it was not fully executed.

Yes that's how it is. Last night I was inside the house and I had no satellite reception, it seems that was it.

Originally Posted by Neil

No, unfortunately that's not possible. The visible file system (contained in region 48) can be re-formatted of course but that won't help anything with this problem, it's not caused by what can been browsed and removed in Mass Storage Mode. The actual OS is a close-held propriety secret, it was loosely based on Linux but is far removed from that now and there's no install media available like with other operating systems.

I am learning more every day about this curious operating system. Also, to my sadness, I am assuming and getting the idea that my nüvi 3790 will never be the same again. Damn the time I updated it.

Originally Posted by Neil

Ah well, it's a 3700 forever now or convert to 3490 and suffer the inherent problems. If the corruption in region 41 cannot be removed then it's over sorry.

Neil, it is true that we cannot do a complete erase of region 41, the tests carried out confirm it, can we do a format of that region? For example, in Ms-dos, a command (del), (deltree) or (format) is not the same as having different operations and results as far as write elimination is concerned.

Neil, would it be possible to transform to 34xx in terms of recovering voice commands, bluethoo, DEM maps, 3D maps, real view (JVC) but with the satellite controller (GPS) (PCB controller?) of the model 37xx? I mention this, because if the 37xx model's radar controllers could be used, we would possibly avoid the car's jumps and the inaccuracy of the GPS.