Car/Auto charger dissected...
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 16 years
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I tried to use my Garmin car charger for the first time only to discover it didn't work. I have had it since Xmas, but until this past weekend, always ran it off batteries. SO I called Garmin last night and they are sending out a new one (about 18 minutes on hold). Great.
But the reason for this post. Since they didn't ask for this one back, today became dissect the charger day and see if I can fix it. Well I now know how the charger works and it turns out the circuit itself is fine. Where is the issue lies is there is a short between power and ground in the USB cable itself. After spending some time with the charger will still together, just opened, it seemed broken at the circuit board. So I desoldered the wires to remove the USB cable side and tah dah! The thing started working. So checking the other side, the cable itself has a short in it. I assume when they added the resistor inside the molded plastic USB end, a short got created, likely from the multistrand shield of the cable having a strand or two hanging loose and got molded against the power wire connection.
I am going to attach it with an Exacto knife later and see what the root cause is. I am can probably splice in a generic USB cable, cutting of the large side of a USB to Mini-USB connector, tack in a resistor at the charger circuit board and soldering in the connector.
I can post back later what I find.
For any techie types who know electronics and are interested in a few details. The charger uses a General Instruments Step Down Switching regulator part number GL2575 (which may no longer be in production. GI is now owned by Vishay.) and also a LM358 Op-Amp to monitor the voltages and shut down the regulator if needed. Only the +5V and Ground wires come from the USB cable. The two data lines are not carried through the cable. The reported 17k resistor used on the normally unused (pin 'x') pin of the Mini-B USB connector appears to be connected at the USB connector and is molded into the connector. As I said above, I will open her up later and see what is really in there.
That is all,
PT
pictures are worth a thousand words
How about some pictures just like the guy who dissected the Nuvi 350
Garmin 38 - Magellan Gold - Garmin Yellow eTrex - Nuvi 260 - Nuvi 2460LMT - Google Nexus 7 - Toyota Entune NAV
Dissected Nuvi 350 Where?
How about some pictures just like the guy who dissected the Nuvi 350
I can't seem to get a hit on this using the search. Can you please post a link? I'd like to open up my 350 to see if I can get a brighter backlight going.
Nice
. . . I can post back later what I find.
Great post. Pls do post what you find.
Nuvi 660 -- and not upgrading it or maps until Garmin fixes long-standing bugs/problems, and get maps to where they are much more current, AND corrected on a more timely basis when advised of mistakes.
Hope the cable carries the X pin on a wire
If you do cut a generic USB cable, please let us know if the X pin is actually connected to a wire on the cable, so that adding the 17K ohm resistor on the regulator end is possible.
Gleam Microelectronics seems to 2nd source the part:
http://www.gleammicro.com/GL2575-V1.0.pdf
I suppose the LM358 was added as an added measure of safety.
.
The charger uses a General Instruments Step Down Switching regulator part number GL2575 and also a LM358 Op-Amp
Interestingly different set of components, to the ones I found in my Nüvi 310 'Vehicle Power Cable' (010-10723-06), detailed at the end of Page 1 of this thread:
http://www.poi-factory.com/node/11120
------------------------ Phil Hornby, Stockport, England ---------------------- http://GeePeeEx.com - Garmin POI Creation made easy »
Link
How about some pictures just like the guy who dissected the Nuvi 350
I can't seem to get a hit on this using the search. Can you please post a link? I'd like to open up my 350 to see if I can get a brighter backlight going.
http://www.poi-factory.com/node/16159
Garmin 38 - Magellan Gold - Garmin Yellow eTrex - Nuvi 260 - Nuvi 2460LMT - Google Nexus 7 - Toyota Entune NAV
The mysterious Pin "X"
If you do cut a generic USB cable, please let us know if the X pin is actually connected to a wire on the cable
Pin "X" as pinouts.ru calls it (or Pin 4 as the USB spec refers to it!) doesn't seem to be accessible in any 'standard' USB cable or mini-USB plug. I'd love to be proved wrong on this - but I've spent quite a while looking (and chopped up a few cables!), and haven't found one yet
------------------------ Phil Hornby, Stockport, England ---------------------- http://GeePeeEx.com - Garmin POI Creation made easy »
Further info...
Gleam Microelectronics seems to 2nd source the part:
http://www.gleammicro.com/GL2575-V1.0.pdf
I suppose the LM358 was added as an added measure of safety.
Ya it is the circuit shown for the adjustable output and then the output goes to the Op-amp which monitors both the feedback voltage and the output voltage. The Op-Amp outputs are tied to the GL2575's ON/OFF pin so if either Op-Amp senses trouble, the ON/OFF pin is driven high and turns off the regulator.
In my case, since the output was shorted at the USB connector, the OP Amp kept the regulator off so it wouldn't destroy itself from over current (possible fire hazard).
Interestingly different set of components, to the ones I found in my Nüvi 310 'Vehicle Power Cable' (010-10723-06), detailed at the end of Page 1 of this thread:
http://www.poi-factory.com/node/11120
I suspect that Garmin simply buys their chargers from different vendors using whatever design they offer and Garmin just orders them with their right angle connector with the 17k resistor added before molding. So you got one charger and when I got mine they had switched vendors or the 200's just came with the other vendor's version.
Well I cut it open and sure enough, there is a 17.4k resistor connected from ground to the 'X' pin. From here on out I will refer to it as "Pin Is Near Ground" or PING pin.
After all, it does ping the Nuvi to tell it to go to navigation mode. Or just looking at the letters PIN is next to G. Yuck Yuck!
OK anyway, I doubt there is anything magical about the exact value. Standard resistor values go 16.9, 17.4, 17.8, etc. So the value was picked from that chart and likely any value in the ballpark of that will work (15k-22k for example).
As already mentioned, the PING pin likely is not normally populated with a wire in standard USB cables, especially if they use twisted pair cables which come in even numbers of conductors. So 4 wires covers the standard, 6 would be required to carry the PING line and I am sure cable manufacturers do not bother.
PT
Garmin nüvi 200 (my first GPS), 780, & 3700 Series. And a Mac user.