Replacing main circuit board

Aug 10, 2014
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Cambridge, MD, Washington DC
In a previous post, I mentioned having crashed my Phantom and experiencing subsequent "Invalid Battery" issues. The cause was a busted connector on the main circuit board, which required replacing the entire board. As I could not wait for the local dealer to get it done (2 weeks turnaround time!), I decided to do it myself. Hopefully my experience will help others who face similar issues.

1. Prepare the Phantom for "surgery". Remove prop guards and props, remove or cut any decals which cover the seam between the top and bottom halves of the body.

My "Amelia", getting prepped.

2. Remove the 4 small screws at the tip of each arm, the 2 hex socket screws nearest the motor mounts on each arm, and the deep well hex socket screw near the landing gear corners

3. Carefully and slowly lift the top half of the body away, taking care to ease the shell around the motors. Pull the top half away high enough to reach in and disconnect the GPS wires from the connector on the circuit board. You can then set the top half aside.

4. At this point, it would be a good idea to get your soldering iron started heating.

5. Before going further, make sure you have plenty of light and take clear pictures of the connectors and layout of the board, getting as close as you can. I thought I did this adequately but wound up having to rewire the Naza on intuition, luck, and a German language YouTube video of a teardown. I didn't understand the language, but the pictures helped.

6. Start disconnecting the wires from the main circuit board. Use some plastic tweezers or a plastic spudger to help pry some of them carefully away from their connectors.

7. The circuit board has 3 sets of wires which are soldered down and covered in white glue. Don't try to remove these from the board. The new board comes with those already in place.

8 The flight computer is the orange box with either Phantom or Naza printed on it. Disconnect all the wires from this unit (again, taking note of where each one is plugged into).

9. Next to the Naza is the radio transceiver. Disconnect the two antenna connectors, a single wire connector on the "front" of the unit, the two connectors on the side, and if you can manage it, the rear wire bundle which is at a tough angle to get to with the transceiver still in place. If you can't get to it, be aware of it when you get to the point of prying the transceiver off the board and disconnect it afterwards.

10. This is actually one of the first really tough parts. The transceiver is held in place by both a small screw through an extended part of the plate the unit sits and some pretty tough double sides foam tape. Remove the screw first, and then gently use a wide thin plastic blade or spudger and begin working it between the transceiver plate and the main circuit board. This tape is really tough so go slow and easy until you can start to work the unit away from the board. You will hear the tape giving way. Salvage as much of the tape as you can to the bottom of the transceiver or have some more ready to go when you reinstall the unit.

11. The Naza is held down in much the same way with the double sided foam tape, but doesn't have a screw to remove. Using the same tools and techniques from the previous step, remove the Naza from the board.

12. With everything disconnected from the board and the transceiver and Naza removed, now comes the not-so-fun part (at least, for me). There are a total of 6 solder points to remove before the board can be taken out. There are two on each corner toward the arms, and two beneath where the transceiver was installed. Use the soldering iron to loosen the solder and a solder sucker or wick to get the solder off enough to free the power wires. Make note of where each is soldered. Red is voltage, black is ground, in the case of the two main points on the side. On the points connecting power to the motors, the white sheathed wire is voltage and the bare one next to it is ground. On these, the voltage wire is slightly further toward the center of the board than the ground.

13. Once the solder points are freed, remove the screws holding the board in place. On the right hand side, two of the screws are holding down a smaller rectangular circuit board atop the main circuit board. The two screws go through both boards to the bottom casing half. Just set that board aside once the screws are removed. Lift out the old circuit board.

14. Install the new board by working backwards from these steps. Lay the new board in place, put the screws in, make sure to lay the small rectangular circuit board in place before putting in those screws, and prepare to resolder the power wires back to their respective positions. Use a good quality solder which can stand up to the stress and temperatures of the drone in flight, especially the main power points below the transceiver. In my testing, the transceiver gets VERY warm during use (as I learned later). I also subsequently applied a dollop of Gorilla super glue to each solder point as another layer of protection. That kept me grounded for an additional 24 hours while I let it fully set and cure.

Once I had everything back in place and reassembled, I inserted a fresh battery and powered it on. Voila! The unit powered right up and I was able to get the Vision app to connect and start checking functionality. I launched the Phantom in my office for just a quick flight and had it up for all of 3 minutes when it cut power entirely and dropped like a rock. The battery remained powered on but the Phantom itself wouldn't power up even after power cycling the battery. I opened it back up and, sure enough, the main voltage wire solder point beneath the transceiver had come off. That was when I decided to also use the super glue for added support. I also cut a small piece of foam and placed it over those two wires, as well as some thing electrical tape. The idea being to insulate that point a bit better from the heat of the transceiver, just in case.

I truly hope this helps others who might need to go poking around inside their Phantoms. I will do my best to answer questions, but please be patient as I am still learning too! I have only had the Phantom since Monday (today is Friday for me, and I crashed it on Wednesday), and this is my first "real" quadcopter.

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