Monday, April 13, 2015

Garmin 765 Loss of Power Fix

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Back in 2011, my wife bought me a GPS to help me find my way around the countryside.  I needed it.  I get lost easily, it seems.  I shopped around and found what I wanted, a Garmin nüvi 765T.  You can read all about it here, and in later postings called out below, under "Previous GPS Postings." 


The device has been fine, mostly, but the power connection has been troublesome.  I was frequently getting this message while en route. 


Fiddling with the power connection in the back sometimes made it recover, but finally, there was no amount of wiggling that would make the power come back on...and the internal battery only runs the unit for 10 or 15 minutes, so that is not an option.  This type of failure has happened twice now. 

Frustrating. 

Others have had this trouble too, and have written about it:
GeekDad66 even tried to fix the problem. 


I decided to do some first-hand investigation on how to remedy this nuisance. 

CAUTION
DO NOT attempt repairs if you are not familiar with safe mechanical or electrical work practices, or if you don't know how to properly solder electrical circuitry.  
I take no responsibility for anything in this posting used by others.  There is a possibility that something described here or misinterpreted from my description could cause the GPS or other electrical systems, including the vehicle in which it is used, to malfunction.   

It turns out that there is a component called the cradle (Garmin Model: 010-10823-07) that attaches to the back of the GPS and contains the 18-position receptacle that, among other things routes 12 volt power to the GPS itself.


It is that receptacle that usually fails.


Here is how I found out.  Lets look inside the cradle.

Remove the single Phillips-head screw.   


The two halves of the cradle still won't come apart because there are four latches inside around its periphery. 

I couldn't force the halves apart with my hands, so I used a small wood chisel applied adjacent to the pushbutton that unlatches the cradle from the main body of the GPS.  It only takes a light bump with the palm of your hand on the chisel to pop open the cradle.  Be very careful not to cut yourself. 


There are two springs inside that will pop out if you are not careful as you open the case.

There are four latches around the inside of the halves of the cradle.  One of them is circled.  One of the springs is visible, too. 



There are two more latches down here.


The inside story:


The 18-position connector:


The body of the receptacle breaks right off the board due to the stresses of the power cable, and not long afterward the tiny wires connecting it fracture too. Mine just fell out when I opened the cradle. 


In most cases, that would mean that the cradle is junk, but a new one costs at least $21, and I am on my third one, counting the original.  This is getting expensive, and I'm a tightwad.

I decided to press onward with a fix.  

The circuit board is marked with the polarity of the 12 volt supply, and there are large enough holes in the board centered in the Positive and Negative pads that can accept wires. 


 The polarity is even marked!


The plug on the power cable I use on the bike (Garmin Model 010-10747-03), and that mates with the 18-position receptacle, has only four active terminals, two for the positive and two for the negative feed from the 12-volt source.  I suppose they use two to make the connections more reliable.  They are what are called bifurcated connections. 



I decided to engineer a two-wire cable connection using 1/8" (3.5mm) miniature phone plugs and jacks (sockets).  The cradle circuit DOES NOT change the input voltage.  It is a simple pass through -- 12 volts in, 12 volts out.   

I went to Radio Shack and bought a mono (2 conductor) audio cable with male plugs on both ends.  Since the cable has two male ends, it is enough to fix two cradles -- just the number I have that need fixing.  This plug will provide the 12-volt source.

Radio Shack
Model: 42-2420
Catalog #: 420242
One cable, two usable plugs

I also bought two in-line jacks, and two more plugs.

Radio Shack
Model: 274-333
Catalog #: 2740333
Radio Shack
Model: 274-287
Catalog #: 2740287



The idea is to cut my Garmin power cable near the plug that mates with the 18-position receptacle, and attach a jack there. 

A plug that I will add to the GPS cradle will mate with it, eliminating the troublesome receptacle.

Since I have a functioning cradle with the receptacle intact, I will also attach a male plug to the end of the power cable I cut off, so it functions as it did originally.  Pictures later. 

First I cut off about five inches of the Radio Shack audio cable, stripped the center conductor, and separated the shield foil and wire, so I can attach it to the circuit board inside the cradle.


Then I prepare a hole just to the right of the receptacle slot for the new cable to exit the cradle. 


It will look like this when assembled. 


The wires in the new cable are attached to the positive and negative holes in the circuit board.  The center conductor is positive, the shield is negative. 


The shield wire, being soldered very close to the circuit board helps prevent the cable from pulling out of the cradle when we are all done.  The undersize hole that was added in the side of the cradle also helps this.  

The positive (+) side is connected to the tip of the phone plug.  The negative (-) to the sleeve.  The ones I used are all mono, two-conductor plugs and jacks, not stereo, three-conductor. 


A thorough description of phone connectors can be found here


I put the parts back inside the cradle, routing the new cable through the new hole.  I glued a small piece of felt over the old receptacle slot to keep the mud daubers and dust out. 

Don't forget the springs.  If you lost one or both of them, you can make new ones from shortened ball-point pen springs.  (I know this from first-hand experience.) 



This is how the cradle looks with the new cable sticking out. 



By the way, the power comes out of the cradle and enters the GPS unit using the following pins in the other connector of the cradle:


More bifurcated connections there. 

Now, to attach the female jack to the cord that I cut the plug off of. 

The opening for the cable in the jack housing is too big for this cable diameter, so I put some layers of heat-shrink tubing over the cable to make it fit snugly in the housing. 


Ready to solder.  Don't forget to put on the heat-shrink tubing and the jack housing onto the cable before soldering!  Correct polarity is red to center (tip), black to sleeve. 


 Soldered connections and heat shrink tubing visible. 


Buttoned up. 




Now, to make the end I cut off the power cable functional again.  It would be used with a cradle where the 18-position receptacle is still intact.




This plugs into the female jack we put on the power cable and converts it to mate with the 18-position receptacle, just like the original power cable worked. 

So here are all the pieces:


The red and the black male plugs mate with the black female jack so you can use the power cable either way -- with the newly-added cable on the cradle or with the plug for a cradle with a functional 18-position receptacle.

Whew.  Did you get all that?  

Rear view of the new cable coming out of the cradle, on bike. 


And a rider's-eye view:


The jack is wiretied to the handlebar clamp. 

This ought to last a lot longer than the troublesome receptacle that came in the cradle.


Notes:
  • If you leave the 18-position receptacle on the board in the cradle, and if it is still functional, DO NOT connect a power cable to the cradle through the 18-position receptacle.  That will make the tip of the added phone plug have a positive 12 volts on it.  If the tip touches something grounded in the vehicle, a fuse will blow, probably in the power cable.  If you need to connect power to the functional 18-position receptacle, then the added phone plug MUST be insulated.  A jack with no cable attached to it could achieve this.   
     
  • The traffic function of the 765T ("T" stands for traffic option), will not work except with the original power cable (Garmin GTM 20) plugged into the functioning 18-position receptacle in the cradle.  That cable has a skinny rectangular receiver in it (at right, below) that mates with other terminals in the cradle. 


    The power cable I use on the bike does not have the traffic receiver, only the power connections. 


Previous GPS Postings:

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Let me know if you find this fix to be useful in solving the power problem on your GPS. 
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1 comment:

Stewie said...

Absolutely great and detailed tutorial. Thank you for this excellent illustrated step-by-step guide!