Introduction: Shock-Proof Your Garmin GPS
Shock-Proof your Garmin GPS to prevent unintended power-downs. I look at a couple different ways to make the fix, and actually do one of them. This project requires soldering a couple of fairly tricky connections inside the otherwise working GPS, so use caution.
I use my GPS a lot, mostly for biking. It's mounted on the handlebar no matter where i'm going - on-road, off-road, everywhere. problem is, after enough hard bounces something goes loose inside the unit and it shuts off. i had this problem a lot with my older Etrex, now i've got a 76cs which worked great for a few months but now has the same problem - enough hard bumps and it shuts off. once the unit shuts off the first time, it usually will do it again and again with very small bumps, so it ends up nearly useless.
Step 1: Tools & Parts
- a couple small screwdrivers (phillips and regular)
- a sharp knife
- some high-temp glue such as hot-melt glue or silicone
- fine-tip soldering iron
- capacitor: 470uF 4V or similar (i used digikey part# 495-2292-1)
- a little bit of flexible wire
You want to get a high-value capacitor but it needs to be small enough to fit in the GPS case - there isn't a lot of room. After I finished it seemed like i probably could have fit something a bit larger in, such as one of the smaller 1000u electrolytic capacitors measuring 6mm diameter x 12mm long. I used a 470uF tantalum which is smaller but more expensive.
Step 2: What Is the Problem With the GPS?
Why is the unit losing power under severe vibration? Somehow an open-circuit is briefly created in the power for the unit. This can happen in a couple of ways - a soldered electrical contact can vibrate until it breaks, or a pressure-fit electrical contact can vibrate enough that it momentarily opens. I've seen many forms of these failures over the years in car stereos, portable radios, and other devices that get bounced around a lot. You never know what happened until you open them up.
The most obvious thing that might be happening is the batteries might be vibrating in the battery holder. This was the problem in my old Etrex GPS, and I was able to fix it by stuffing foam into the battery holder. I tried that trick first with the 76cs when it started acting up, but it didn't help so I concluded the problem was internal.
Lets open it up and see what's going on!
Step 3: Open the Case
First, remove the 8 small phillips-head screws on the back
Second, pry off the front of the case using a flat-head screwdriver inserted above the rubber seal. The seal at first seems like it is glued together, but it is not. go around the rim slowly prying and the front of the case will eventually loosen and come off.
Step 4: Unscrew the Button Panel
You don't have to unscrew the button panel for the fix I made, but it's easy to do and you can see the likely cause of the problem and another possible fix.
Remove the two screws that hold on the button panel. Underneath you can see the connection to the battery is made through a press-fit against the circuit board. See the 3rd image, where i've highlighted the battery case terminals and the contacts on the circuit board that they press against. The first time I had the problem with the GPS, I tried fixing it by slightly bending the battery case terminals where they poke out of the white rubber seal, to make sure they were pressing hard on the circuit board. This fixed the problem for about a month, so I concluded this was the cause of the problem.
So, we've got two possible ways to fix the problem: (1) fix the press-fit connection so that it never vibrates open, and (2) make it so that even if the press-fit vibrates open, power is not lost.
I decided to do #2: by adding a capacitor to the GPS power input, you can make it so that it doesn't care if there is a momentary loss of power during a hard shock. as long as the power connection is solid when the unit is not vibrating, this technique will work.
Lets momentarily consider how we might do #1 though: basically, by soldering the battery case terminals to the circuit board. This is a bit tricky to do because of the bottom-side connection, and because if the circuit board is moved at all the buttons won't work anymore. but i think it is possible with some care, probably the best way would not be a direct solder joint but to attach a thin wire between the connections and possibly melt the case plastic enough that the wire can be embedded and the circuit board is still flush on the mount.
Step 5: Remove the LCD Screen
The screen is not screwed on, it is press-fit on plastic posts so just gently pull it away from the case at the angle shown in the photo and it will come off. it is still attached with an electrical cable. flip the screen and lie it face-down out of the way at the bottom of the GPS case so we can work on the main circuit board
Step 6: Identify the Fix
We will solder a capacitor onto the main circuit board right where the power comes in from the battery. this way if there is a momentary disconnect of the battery, the capacitor supplies the power until the battery is connected again.
The tricky part is that there is not much free space inside the GPS to put a capacitor! We'd like to use a large-value capacitor since the bigger the value, the longer it can power the GPS for. I just looked for the biggest one i could find that would fit the case. It turned out that i probably could have fit something a bit bigger in, but i didn't know that until i finished. my loss is your gain!
By carefully inspecting the main GPS circuit board, I was able to find where the battery power came in. It is actually marked pretty well on the board, and there is a small test point on the board we can solder to for the positive terminal. I confirmed my guess with a continuity tester. for the negative terminal, there are quite a few spots on the board where we can solder to. i've marked these locations in the photo.
I then located a spot on the board where I could glue the capacitor without it getting in the way - off to the side of the LCD.
Step 7: Glue on the Capacitor
It will be easiest to glue the capacitor onto the board before trying to solder it. Use a high-temp glue so that the glue doesn't get weakened when you solder right next to it. I used hot-melt glue, but silicone should work also. wait for the glue to dry before continuing.
make sure you orient the capacitor properly with respect to the + and - terminals so the connections will be easy.
Step 8: Solder the Capacitor to + and -
Cut two little bits of wire and solder the capacitor terminals to the spots where we identified the battery input.
make sure to use thin, flexible wire to avoid putting strain on the small connections - you don't want your fix to cause new problems with vibration! you can put a little glue on your added wires if you want to make sure they stay in place with lots of vibration.
Step 9: Put It Back Together!
i've been using the fixed GPS for a few months now with no problem. if i do have a problem again i'll probably try the other possible fix i talked about - hard-wire the battery terminals to the pcb.