I wanted to change the backlight LEDs from amber to blue, red or white. Red would be good so as not to mess up your night vision. But I didn't have any LEDs that would work at the drive voltage being supplied. :( By this point I had documented how to take the device apart, so I thought I might as well put it up here.
If you are planning on changing the backlight, you will need two 3mm round (or flat / smd) LEDs that will shine brightly at 1.95V.
Taking the etrex apart and putting it back together again was surprisingly easy, but a little painstaking. Looking at mine now, you can't tell it's been apart.
Step 1: Dissassembly - Part 1
Take off the battery cover and batteries. Remove the rubber surround by pulling. It's stuck on with glue. Start at the top where the serial connector is. Don't pull too hard, it's one piece. Place it to one side to make sure you don't get anything stuck on the glue, you can reattach it as it is when you are finished.
Step 2: Dissassembly - Part 2
The top and bottom parts of the case are sealed by two layers of tape. The first layer starts and finishes at the bottom of the device. Use a small knife to lift the end up and peel it off. I stuck the tape on the end of my desk to keep it safe and so it couldn't stick to anything else. You need to reuse the tape as it's shaped to fit the profile of the device.
Step 3: Dissassembly - Part 3
Remove the second layer of tape. This layer is thicker and not shaped. It has a better glue, but also stretches, so don't pull too hard as you peel it off. The join was on the side of my device. Again, I used a small knife to lift the edge.
Step 4: Dissassembly - Part 4
This is where we open up the case. The two parts are now only held together by a series of clips. There are no clips at the top of the device so I started there. Pry the case apart a little at the top and using a small knife, open up the top clips on the side of the device. Do this by inserting the knife into the slot, not the rectangle. The clip should pop apart undamaged. If it doesn't you're probably not using the right amount of force. I could easily apply the force with my fingers, no extra tools are required. The clips are only small, so would be easy to damage. Once the first clip opens, the rest follow quickly with each being easier to open. The case should now be apart. Be careful, the back half is connected to the PCB via a cable terminated at a connector. Remove the connector.
Step 5: Backlights - Parts 1
Details of the current LEDs.
Left LED: 1.95V +ve on bottom pin
Right LED: 1.95V +ve on top pin
Step 6: Backlights - Parts 2
With the LEDs illuminated.
Step 7: Back Together
Reassembly is very easy. Reconnect the serial cable, snap the two halfs back together, then put the two layers of tape on, then the rubber seal.
Here's mine all back together, unfortunately still with the same colour backlights. :(