How to diagnose if your flight controller is dead (Blue LED only, can't connect with betaflight)

I have seen a large number of posts over the years from people who have similar issues with their flight controller, and ask for assistance with troubleshooting. The symptoms typically include only seeing a single blue LED light when connecting over USB, and not being able to connect to it using betaflight.
Here in this short video, we will walk through a few simple things that we can do to determine if the CPU on our board is actually dead.

[@bugsy742]

2 years later and still very relevant 👍 Thanks for making and sharing this mate 🙏🙏🙏

[@dpt560]

This was cool how short the video was and how accurate it was. After a hard crash the fc leds stopped working but the vtx and rtx both still had power and leds on those little boards were on. ESC motors beeped but the last fc beep wasnt happening. I figured it was the fc but i did that finger trick and holy shit that puppy was piping hot. Thanks for the good info!

[@alloutofdonuts3998]

2 years later…I fricken learned something today boi!!!

[@ErgoFPV]

Man, checking the 3V rail is such a brilliant idea! I definitely learned something today :)

[@davidmgillmer]

Your somewhat Satirical commentary and helpful informative no nonsense video got you my vote man!!!

[@MoralConflict]

Nice!! Methods and explanations not seen in other videos. Keep up the good work. Subscribed!

[@andrewortiz3770]

i love your video, it was extremely helpful and your sense of humor made it all that much better as I am having a bad day and needed that laugh. Thanks!!

[@MnM_FPV]

My Matek 722 FC crapped out on me the other day and was looking for a way to see if my CPU is dead, thank you for sharing and great video! Subbed!

[@zdanek]

Hi. If you don't have THERMALVISION nearby ;) you can use pure alcohol and little brush. Just brush regulator or CPU with the alcohol and watch it vaporizing. If it's very rapid it's sure that it's working hard or is shorted to the ground. Cheers.

[@JohnDoe-kl8cd]

Would you know how to troubleshoot why a specific uart port (and in my case the 5v rails below the row of servos) are not outputing power?

[@enjoyyourlife2518]

I love you ! I thought I fooked it . Sux being a newby . Im going to become an expert at going to my local fpv within no time

[@erlandfpv]

Hi, want to ask what means, white led solid in fc? when we plug battery , and cannot connect or any sign when just plug the usb, thanks...

[@darannadeau9999]

Is there a way to fix the 3v3 pad? Because i think mine is dead but i dont see any hot temperature

[@quincypurcell5222]

Thank you so much now I know what's wrong! 👍

[@CarbonGlassMan]

My Mamba F405 mk3 FC just died today. For no reason it seems. I burned my finger on the 3.3v regulator. Does that always mean the CPU is toast too or can the regulator short out and not fry the CPU?

[@daviddouglasspeidel]

What is a 662V? I think it’s bad on my tinyhawk 2 FC. I get 3 beeps and some lights when I plug in the battery but nothing happens when I plug usb into the computer. There is also a 662K on the board and I can find those online but I can’t find 662V. Help me Obie-Wan your my only hope.

[@brodyport6395]

About to go check mine. But I’m not even gonna be mad if it is because this video was amazing. (Ok maybe I’ll be a little mad but

[@ngcreations6552]

Hello brother Same problem my flight controller cc3d it's only show to blue light not taken bootloading option

[@giangulli]

"Ohm my god" hahah legend thanks for the vid!

[@jrowe88]

Helpful video! I have a dead board that is showing 3K Ohm on the 3V rail, but the f7 MCU gets blazing, burn-my-finger hot. The 3V regulator is a normal temperature. What might this suggest? Is the MCU dead or could there be a short between pins? Any way to troubleshoot this further?

[@SardonicEnrapture]

I had one that behaved the same. You can remove the MCU and then measure the voltage on the 3V rail; If it's 3.3V without the MCU installed, then the MCU is dead with an internal short, if it isn't, the culprit is elsewhere.

[@CarbonGlassMan]

Finally a video that shows a board just doing the first three tones and not the last two. Mine did that when plugging in a battery, but plug in the USB and then also a battery and it made all 5 tones. What could cause that?

[@SardonicEnrapture]

The 5V regulator on the FC is dead, probably. Measure the 5V rail when on battery, but not USB. If it's anything that isn't right around 5V, then you can probably get it working by feeding any unused 5V pad with a pololu or similar between the main battery and that 5v pin (that is now 5V in and not out, as it would normally work) I have gotten many boards with damaged regulators to work by doing this, but if the FC has a diode on that rail, then it wont work (this is Rare) Of course it would be better to replace that 5v LDO, but not if you don't have the required tools....

[@CyberWallX]

Hey man, very cool video, learned a lot in under 5mins. I have a quick question: yesterday a crash ripped out the 3 control connections of an ESC. I resoldered them and it seemed to work. But today i had a small crash again, nothing too bad, but the FC doesnt fully initiate anymore. Is it possible that bad soldering shortened the control connections and this grilled the FC? I am ashamed i dont have a multimeter atm, but ill get me one soon :D Anyway, i would highly appreciate any kind of help/opinion

[@CyberWallX]

oh and its an age old flip32 btw

[@Kheine89]

Hey could you help me maybe? all i did was connect my fc to usb, worked great and changed one setting which was sbus to ibus and now fc is showing solid red led. Not a hot board just not responding... thanks in advance

[@RecursionLabs]

Try re-flashing the board with full chip erase. Factory reset basically.

[@DudaZachary]

what if the board doesnt have a 3.3v pad? can I use a 5v pad?

[@RecursionLabs]

I have not seen one without, but no. The 3.3v pad is relevant because it powers the CPU.

[@Whyyouhere_]

I have that simple drone with brushed motors(cheap, i know) after connecting remote to drone, when i starts throttle all leds blinking and it won't throttling. Someone please help me 😣😣

[@rocheuro]

thanks to your tutorial I just checked my old CC3D is burned to hell. thanks! . not so happy thou ;)

[@RecursionLabs]

At least you have an excuse to upgrade :)

[@seth.heerschap]

Super helpful, I learned something. But my issue is that my LED is dead, but the microcontroller doesn't appear to have any shorts. Also, when everything is connected, the FC won't connect to betaflight and isn't making those two long beeps.

[@RecursionLabs]

Could be a bad voltage regulator.

[@seth.heerschap]

@@RecursionLabs you might be right. I ended up just replacing the FC. $62 =/

[@MikeLof]

Hey, thanks for the video! You have given me hope that my broken CLRacing F4s may still yet live. There is resistance when contacting the multimeter on 3V and ground. I have been troubleshooting for days. It does not connect to any computers (even though it has before). I've tried holding the boot button while connecting to try DFU mode. nothing. I've tried rebinding the receiver. It's strange because this Armattan Marmotte RTF has flown many times without a problem. The day it stopped working, I landed in some thick dry grass and then tried to take off again. A prop was caught in the weeds and the quad flipped. I disarmed, picked it up and cleaned it out, and turned off the transmitter to relocate. When I set up for a takeoff, the quad would not arm nor show the OSD, but video worked. When power is connected, it beeps 3 times, but does not finish initialization. My transmitter says telemetry recovered / lost when the quad is powered on / off. Can you point me in the right direction to continue troubleshooting?

[@Jingleboy14]

Did you ever find a solution? Same boat - LED is red, no obvious shorts (heat is normal), resistance between ground & 3v3 volt. Tried flashing, Betaflight claims to see FC, writes firmware, but still red LED

[@dedeirvan9537]

@@Jingleboy14 I have led red too but when I touch my FC, FC hot.

[@shurumellafpv8188]

Mate Please , my Success F7 shows solid red light forever , Pc can’t see the FC after flash . 3V seem ok How I can put the FC to work again ?

[@55amps]

I have the same problem, did u ever find out?

[@65t1]

@@55amps Same here too. Any luck?

[@55amps]

@@65t1 no, I sold it on eBay as is lol

[@65t1]

@@55amps That might be my best bet too at this point.

[@questplayes4099]

Hello I have no odd on my goggles I but I already replaced the vtx and the camera is it possible that my flight controller is broken or my goggles?

[@CorrexPoE]

do you get no videofeed at all? if you get a grey picture that means its the OSD chip on the FC that is dead. simply connect VID In and VID Out together, it will work again, without showing osd

[@CorrexPoE]

(both yellow wires of vtx and camera, remove both from FC and solder them together) You can buy an external OSD instead of replacing the FC

[@Spideystrat]

Great vid. My f4 flew fine & now won't connect to Beta w no LEDS. Power to RX tho ...

[@eternalfpv9461]

Did you ever sort is out? What was the problem

[@Spideystrat]

@@eternalfpv9461 Fc dead, replaced it

[@davidanderson6222]

Right now it seems I can’t order a board from China these days, so now it’s time to bring some life to at least one fc in my fc graveyard. Thanks much , great tips

[@_ShaDynasty]

well that settles that. just ordered a new one lol.

[@raymondbriceno3276]

ya cause we all have volt readers

[@inabyt]

Yeah my finger is burning off