I killed my GPS receiver! :-(

[stewed]

I wanted to place the GPS receiver in the back of the car and needed a longer cable. However, I accidentally used a telephone extension cable which turned out to be crossed (switching the power and ground pins) and this seems to have killed my Tomtom Navigator II GPS receiver!



The LED doesn't light up anymore, and Navigator II can't communicate with it.



So be careful, people! If you need a longer cable, make sure you're using the correct type of extension cable!

[DavidW]

Oh dear. Unless hardware is specifically protected from reverse polarity, applying incorrect power polarity normally does catastrophic damage.



If you can open up the GPS module, you may be able to figure out what has happened. However, unless there's any protection circuitry (look for diodes or a bridge rectifier, possibly with one or more fuses), the chances are that your GPS module is ruined.





The problem with using diodes to protect against reverse polarity is that if you run the incoming power through diodes (or a bridge rectifier) to ensure correctly polarised power, you suffer a voltage drop. An alternative would be to use a diode that conducts if reverse polarity is applied and blows a fuse or temporarily opens a self-resetting fuse, but that may not act quickly enough to save chips and other semiconductors.





Hopefully you can get hold of a new receiver cheaply enough. Maybe a hunt for a 'raw' Leadtek 9532 - that is one with no cable other than the RJ11 - will succeed and get you back in business. It won't have the TomTom casing, unless you can move that across, but I'm sure what matters most is having a working solution.



If you open up the dead GPS module, you could post pictures of it for anyone that wants them - though I appreciate that is very scant consolation.







David

[Dave]

We've had several forum members that have used a modem extension cable from PC-World (5 metres), and this works well. Maybe the telephone cables cross pins over, I would think the modem cables would be okay otherwise you would see something similar happening to the modem like you experienced with the Leadtek mouse.

[stewed]

DavidW, I managed to get hold of a "raw" Leadtek 9532 with an RJ11 cable rather cheaply, so I'm back in business!



Dave, my description of what I did was rather sloppy. The phone cable wasn't crossed, it was a female-RJ11-to-female-RJ11 adapter I used to connect the GPS reciver cable and the phone cable together that had its wires crossed. I can't figure out what the point is of having the wires crossed in the adapter, though... When do you need that? Oh well, I guess I have learnt my lesson: always check the connections BEFORE plugging it in.

[DavidW]

Glad you're back in business! You could still open up the blown receiver - there's pictures on this site of the inside of a 9531, but not a 9532.



The adapter sounds as if it could have been a crossover adapter for use with RJ45 Ethernet connectors (to link two MDIX or two MDI ends together - in particular, two twisted pair network cards together). That assumes, though, that it's RJ45 (8 way connectors). If it truly is RJ11 (6 way connectors with only the centre four pins populated), then I haven't got any explanation.



If it was an RJ45 crossover adapter - and if the TomTom connector really is an RJ11 (not an RJ12, which has six ways and six populated pins) I am stumped - as an RJ45 crossover wires 1 to 3, 2 to 6, 3 to 1 and 6 to 2. On RJ11 (only 3, 4, 5 and 6), this wouldn't wire anything up - but on RJ12 (2 to 7) this would wire 2 to 6 and 6 to 2.







David

[stewed]

DavidW, the adapter truly is RJ11 (centre 4 pins populated), and so is the Tomtom receiver's connector.



I will do an "autopsy" on the dead Tomtom GPS receiver and take pictures of its "guts" as soon as I get some spare time.



I'll post back here when I have some pictures to share.

[DavidW]

I guess I should say:



stewed's TomTom 9532 - Rest In Peace (or should that be Rest In Pieces?)



It'll be interesting to see if the internals are any different to the 9531 already pictured on the site.





Meanwhile, I wonder what the wiring was in that coupler and why it wasn't wired straight through. Some questions just aren't answerable, though.







David

[stewed]

I took some shots of the dead Tomtom GPS receiver and uploaded them here.



Dave, please feel free to copy them and use them in any way you want.

[Dave]

Thanks Stewed, I'll grab these and put them into an inside article.

[Jtonline]

As I understand it, RJ-11 cables and adapters tend to come in two types:



Straight through for data applications



1-1

2-2

3-3

4-4



and reversed for telephone applications



1-4

2-3

3-2

4-1



So you have to be careful what combination of RJ-11 cables and adapters you use.



If you have a cable terminated with clear plastic RJ-11 connectors, hold the ends of the cable with the metal contacts facing you. Make sure both ends are pointing in the same direction. Look at the order of the coloured wires inside the connectors. If the colours are the same in each, it is a "straight" cable. If the colours in one are the opposite way around in the other, then it's "reversed".



With the solid plastic adapters you're probably going to have to look carefully for any tech specs on the packaging or test with a multimeter to be on the safe side.
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