I had a TomTom One unit which although being quite old now still works, however the DC charging socket on it was broken so once the battery ran out it was impossible to charge it up again, thus rendering an otherwise working unit useless.
Originally I tried replacing the internal DC socket with an external one, and although this worked the connection was a little temperamental and would only charge if the plug was in a certain position and looked a little ugly with wires hanging out of the unit, this wasn't really that useful either.
After a bit of head scratching while thinking of the best way to proceed I suddenly thought of the mini USB connector which is used to connect the unit to a PC to transfer data to / from the SD card. Mini USB plugs are readily available and provide an excellent electrical connection once they are plugged in and USB car chargers can be found on ebay for under £3 each. Initially I intended to remove the PC functionality from the unit (as I had an SD card reader), but I found that the unit can charge the battery and still works as it should when connected to a PC even on the 500mA a PC USB port provides.
The modification is very easy, involving soldering a single wire inside the device and means I now have a fully functional GPS unit again.
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Step 1: Tools / Materials
TomTom One GPS unit
Automatic centre punch
2mm Allen Key / screwdriver
Basic soldering skills & equipment
Step 2: Defeating the Anti-Tamper Security Measures
The case is secured by 4 anti tamper screws on the back, these are standard 2mm Hex scews with a spike in the middle to prevent normal screwdriver bits or allen keys being used, however, as the spike is fairly thin it can be snapped off fairly easily. Using an automatic centre punch repeatedly "hammer" the spike from one side until it either snaps off or bends out of the way. You can then remove the screws using a 2mm hex screwdriver or allen key.
Step 3: Bridging the Gap
Once the unit is open the modification is easy, you just need to solder a wire between the 5volt track from the USB connector and the 5volt track from the DC charging socket.
There is a large solder pad you can use for the DC charging side, but for the USB track you will have to scratch some of the green insulation coating off the track to expose the copper underneath to solder the wire to.
I have highlighted the 2 tracks you need to bridge in orange in the second picture.
Step 4: Finish
Just re-assemble the unit and plug in a USB cable, you should see the green charging light come on on top of the unit, congratulations you have successfully modded your unit.