New Sailfly X - battery won't power on quad, USB still works

While flying the Sailfly x yesterday, power completely cut out, loss of control and vision.

Once I found the quad it appeared the battery was simply dead, however it was only 45 sec into flight time with the GAONENG 3s 300mah.

The quad powers up with the USB connected, the motors actually do work once I plug the battery in…
Therefore does this mean the issue is purely with the XT30/voltage regulator which is soldered to the FC, not giving proper V to power up the quad? But still enough to make the motors run once the USB has powered up the quad?

Again, there are no LEDs lighting up or sounds when plugging any battery in, only with USB.
The motors don’t work with only USB (normal), however if I plug in the battery, the motors work as long as the USB is still plugged in.

I do not believe there’s any problem visible, perhaps the regulator is blown? The ‘100’ labled chip on the board in the photos seems to wiggle slightly, otherwise everything seems ok.
Since the motors still work with the battery is the FC still salvageable?


Thank you,

I think you have answered your own question, probably the cheapest way to fix would be a small external BEC
something like this 3A/5A/7A/15A BEC Brushless UBEC For FPV Receiver Sale - Banggood UK-arrival notice-arrival notice

Thanks Dale

Do you think I could just buy this instead? Since both will require soldering it seems?
Happymodel XT30 Plug Pigtail Power Wire with 100μF Capacitor

No, that’s just the power pigtail with a capacitor, you need a BEC (like the one Dale linked above) and solder that between the battery + and 5v pads.

Yes that is EXACTLY what you need. DO NOT by a BEC, I don’t know why those guys are telling you that. They were used back in the day when receivers and servos needed a separate battery, and the voltage needed to be stepped down. If you put that on your main terminal it will step down voltage for your whole quad. The capacitor you posted is what happy model is shipping all their 2-3s quads now, because of the problem you were having. The capacitor just takes in voltage spikes and holds onto it until the spike is over. It will also clean up your video feed. On bigger quads, people put like a 750-1000uf on xt-60, then little 100-330uf on each ESC, to get super clean video, and protect the electronics.

Thank you everyone, it is clear now. Also fortunately happymodel is finally responding and let me know to ship back to China for replacement

@Sunshyn-RFF what are you talking about??? :confused:

From OP’s description it’s perfectly clear that the BEC has dies, which is a really common thing to happen on these tiny whoop AIO boards. No one told him to put it on his main terminal, it’s supposed to go between main terminal and one of the 5V pads on the board to replace the now missing 5V source because the BEC died. Please don’t spread this kind of miss-information.

Maybe just some confusion, but I do agree if the BEC died on your FC, it’s cheaper to just use an external bec rather than replacing the entire FC. But also using an external bec is not required for most flight controllers that are working fine…

well im glad i was working shifts you put it politely, clearly didn’t read the OP post. buy a power lead with a cap on and have the exact some problem ( well sound advice that)

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It is perfectly clear, the little thing that he said is loose is a DC to DC buck converter not a BEC. And according to press release from HappyModel, was 1of 2 main causes of all the CrazyBee F3/F4 boards frying, the other being a MOSFET. It happened especially after converting from the 1s JST PH2.0 plugs to the XT30. They also are extremely hard to replace. These boards are on the Mobula7, Sailfly, Trashcan, Larva and a few others. HappyModel’s official fix for it was to attach a 100uf capacitor to the battery terminals or in line on the plug itself. Now the Sailfly shipped with an XT30, mine came with the capacitor already installed, but earlier versions did not. So if the OP had one of the early ones, the link he posted is the EXACT PART HappyModel suggests. If you sent in your old board they’d send you a new one with the XT30/cap combo already attached, and all their current models now have a cap on it.

Now, yes a BEC, well a UBEC, which you did link correctly, is what some thought would work also, before HM came out with press release. One guy on YouTube tried a UBEC, and it didn’t really work, it created so much noise on that little quad the video was almost not flyable. He then tried a step up/step down regulator, which made the video better, also making him realize that regulating between battery terminal and source. doesn’t supply enough for the OSD, so you lose that, and it wasted a lot of voltage in the form of heat.

That is why I posted what I did, I was in an hurry and needed to be somewhere, but didn’t want OP to get the wrong part. I apologize if I came off rude to you or your post, that was not my intent. I also wasn’t spreading mis-information, I’ve had to replace two of these boards for exact reason and they fly perfectly now.

Here we go again… I guess you are talking about this: Happymodel XT30 Plug Pigtail Power Wire with 100μF Capacitor – Happymodel

So this capacitor could avoid the risk of burning the mosfet or the 5v regulator at the moment of power on

Yes, adding a capacitor should help to stop the bec from burning out. Will it help once it’s already burnt out? No.