Lost my video signal today. FC is as noted in the title. Troubleshooting determined there is no 10V power on any 10V pad or at the pin in the digital VTX connector. I assume this means that the BEC is toast.

I get full startup tones, 5V pads have 5V, and everything else is working as far as I can tell.

I see some charring on the underside of the board:



Is there any solution other than replacing the FC?

I ordered this FC because I can get it overnight from Amazon, it is only $40, and it seems to have the functionality I need: Amazon.com: GoolRC GF30F722-ICM F722 F7 HD Baro OSD 5V 10V Dual BEC Flight Controller 3-8S 30.5X30.5mm. Since it's from Amazon, I can return if if it doesn't work out.

If the FC is working except for the 10V, you can get an external BEC. Or try to fix it.

Is the little 10V bridge still intact?

(19-Oct-2023, 12:24 AM)voodoo614 Wrote: If the FC is working except for the 10V, you can get an external BEC. Or try to fix it.

Was thinking about that. I have a BEC from my Cinebot30 that has been decommissioned. May try to use that.

How would I fix it?

There is no easy way to explain how to fix it. Because you have to start troubleshooting what got burnt and what may be shorted to ground. Once you identify some faulty components, you can desolder them and replace them. Just from the photos, I see some bad looking caps. Most likely the 10V IC is probably also toasted. Honestly, fixing FC is more for knowledge and fun. By the time you buy a bunch of components, it might not be worth it.

I can’t find a good clear photo of that side of the board online, but most likely, that board is using two MP9943 voltage regulators- one for 5v, and one for 10v.

I’ve put red dots on what is likely the voltage regulators in the attached pic below. You can confirm that they are MP9943 by reading the top of the chips- if it says, “AMG*”, it is an MP9943.

So, one is 5v, one is 10v. Based on the burn marks, I’m going to assume that the top one is being used for 10v.

If you look at the datasheet for this voltage regulator:
https://www.monolithicpower.com/en/docum...nt_id/865/

You’ll see that pin 1 is used for voltage out. The actual voltage is determined by resistors. You’ll find three following the pin 1 trace- one inline, then one going to ground, and then another inline.

So, take your multimeter and see if you can read voltage on pin one, and what voltage you’re getting after that second inline resistor.

If you’re not getting any voltage, you know your voltage regulator is likely dead, and you can replace it if you’re capable of hot air work.

(19-Oct-2023, 12:42 AM)Suros Wrote: Is the little 10V bridge still intact?

There is no such solder bridge across these pads, nor was there ever. It looks like that's for some application that's not relevant to me. Everything worked fine without any solder bridge here.

(19-Oct-2023, 03:45 AM)Lemonyleprosy Wrote: I can’t find a good clear photo of that side of the board online, but most likely, that board is using two MP9943 voltage regulators- one for 5v, and one for 10v.

I’ve put red dots on what is likely the voltage regulators in the attached pic below. You can confirm that they are MP9943 by reading the top of the chips- if it says, “AMG*”, it is an MP9943.

So, one is 5v, one is 10v. Based on the burn marks, I’m going to assume that the top one is being used for 10v.

If you look at the datasheet for this voltage regulator:
https://www.monolithicpower.com/en/docum...nt_id/865/

You’ll see that pin 1 is used for voltage out. The actual voltage is determined by resistors. You’ll find three following the pin 1 trace- one inline, then one going to ground, and then another inline.

So, take your multimeter and see if you can read voltage on pin one, and what voltage you’re getting after that second inline resistor.

If you’re not getting any voltage, you know your voltage regulator is likely dead, and you can replace it if you’re capable of hot air work.

Thanks Lemony.

The new FC was on my porch this morning, so I started working with that. I have a question about it, so I'll put that in a new thread.

I have no experience with hot air work. I'd probably enjoy learning about it, but that's probably in the same category as a 3D printer right now. I already have the parts for another build, so I want to get this quad flying again, then start working on the new build.

I may check out the voltages on the pins, but I can't really see the traces, even with my mag glasses. I just ordered a digital microscope, so I'll take a closer look at it when I get that tomorrow, just for the learning experience.

(20-Oct-2023, 12:53 AM)aerokam Wrote: There is no such solder bridge across these pads, nor was there ever. It looks like that's for some application that's not relevant to me. Everything worked fine without any solder bridge here.

I wonder if that's just for the VTX power pad. Either way, I said that before I noticed the toasted parts as I was quite tired.

(20-Oct-2023, 04:28 AM)Suros Wrote: I wonder if that's just for the VTX power pad. Either way, I said that before I noticed the toasted parts as I was quite tired.

Those are jumper to put 5V or 10V going to the VTX+ pad. There is also a 10V pad that OP could have used for DJI without any jumping.

I finally got around to disconnecting the BEC from the Cinebot LED strip, and connecting it to BAT on the FC. The BAT pad I tried first was inop, which I didn't check before connecting to the ESC for power, but there was one on the other side of the board that worked.

I have 11.8V at the BEC out, so should be able to connect a wire from there to the 10V pin on the O3 connector. The cheapo FC I installed is working great, so I now have a spare FC.

Only problem I've had with the replacement FC is the O3 connector detached, but I just soldered the O3 wires to pads instead.