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Eachine Mustang P-51D Electronics Repair

May 11, 2020

This post describes how to repair the electronics of a Eachine Mustang P-51D after reverse battery connection


Recently, I bought a 400mm Eachine plane for flying around in the park. At a weight of 50g it is a perfect park flyer with only very little risk of injuring someone. This is quite a nice change compared to my Wifibroadcast quadcopter. Here is a picture of the plane:

Eachine P-51D Mustang

Being so small, the plane is still extremely stable in the air thanks to its active stabilization system. In fact, it flies like a much larger plane in a very compact form factor. I really like it.

But what I seriously dislike are the battery connectors. It is quite hard to determine in which direction you need to connect them. What is even worse is that they actually can be connected in reverse! This is really a no-go for a consumer product. I found this out the hard way, my plane released the magic smoke and was dead from that point on.

Since I only had the plane for a couple of days I thought about turning it in for warranty. But meh, how boring is that? You just write stupid emails with customer support, wait and learn nothing in the process. So I opened it up and repaired it by myself. This is what this post is about. It is just a hint to everyone who was as stupid as me (and connected the battery in reverse) or who just wants to know what is inside before opening it.

Disassembly

Disassembly is rather easy. All foam parts are glued together with some kind of very flexible glue that lets you lift off the main wing a bit. Between the wing and the fuselage the glue then gets stringy and can be cut with an exacto knife. You just have to be careful and patient and after a minute or so the wings should be detached. Under the wings you find the main PCB with the elevator and rudder servo motors:

To remove the PCB you first need to unscrew the connectors of the servo motors. After the screws are removed, these can simply be pulled upwards. Next, the PCB has to be removed from the fuselage. Again, the same type of glue is used so you have to carefully bend the fuselage and cut the strings of the glue. Finally, you need to unsolder the motor wires (marked M+ and M-) and unplug the aileron servo connector.

Repair

The actual repair is quite simple. All that was blown was a 3.3V regulator. Luckily, it acted like a fuse and protected the microcontroller, sensors and radio that are supplied by it. You can see the the part and its connections in the following image:

All you need to do is to replace the regulator with another one. The electronics consume roughly 40mA so every regulator above 100mA should work with sufficient safety margin.

I found a slightly bigger regulator in my box of scrap PCBs and mounted it to the PCB:

The input of the new regulator is connected via a thin wire that could act as a fuse. This way I have some extra protection in case I am stupid enough to connect the battery in reverse again (which is quite likely… ).

After I added the new regulator I was very happy to see that all the other components survived and the plane is able to fly again.

To glue everything back together I recommend “Uhu POR” which is specifically made for flexible joints. To my eye the original glue of the plane is very similar to the Uhu product.

Conclusion

I can highly recommend the Eachine plane. It is a really fun toy and combines the good properties of a large stable plane and a compact easy to carry plane. I cannot recommend connecting the battery in reverse, obviously. But it is not the end of the world.

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