Hi,

So I bought a new speedybee f405 v3 fc as I saw some great reviews on it for a budget flight controller. After plugging it into my pc and updating firmware I soldered on my RX, VTX and camera. I then setup all the basic settings using betaflight. I then mounted the fc on my stack and plugged it into my esc with the included cable. Upon plugging in the battery I get 3 beeps(so esc is fine) and then 2 beeps(so fc is communicating), however the only led is the red power led, which is dimmer than usual. The RX and VTX have no power. I then plug my fc into my pc and both the red light and the blue light are bright, and the rx powers up, still no vtx power. When I go to the motors tab I can't spin up any of the motors.

I used a multimeter to test the following:

• 5v pads - got a reading of -0.3v
  
• bat pad - got a reading of -0.5v
  
• checked diodes - all were healthy
  
• checked ohms on 3v3 and gnd - got a reading of 1.2
  
• checked for continuity between nearby solder joints and didn't find any shorts
  

Any help would be appreciated.

Something is dragging your voltage down.

First thing I’d suggest is removing all peripherals (vtx, rx, cam, and anything else you’ve attached such as a buzzer or gps).

Re-seat the esc cable and make sure that all pins are straight.

Plug in to battery power and see if that power led glows bright.

If it doesn’t, measure the voltage on the 5v pads again- if it’s significantly lower than 5v, you’re likely having an issue with the fc’s 5v regulator. You can bypass that by wiring an external bec to a 5v pad.

If it is glowing brightly, then:
One by one, start reinstalling peripherals, testing with a battery each time to make sure all is well.

Also, make sure that the total amp draw of all peripherals isn’t higher than what the board can handle. (ie: a vtx that draws 1.5A on a board that can only handle 1A [that’s just an example, I didn’t look up the specs of your specific board]).

Edit- also, inspect all boards carefully with a magnifying glass to check for stray solder balls and wire whiskers.

What vtx are you using, and how is it powered? (5v pad, 9/10v pad, vbat?)

(05-May-2023, 06:21 PM)Lemonyleprosy Wrote: Something is dragging your voltage down.

First thing I’d suggest is removing all peripherals (vtx, rx, cam, and anything else you’ve attached such as a buzzer or gps).

Re-seat the esc cable and make sure that all pins are straight.

Plug in to battery power and see if that power led glows bright.

If it doesn’t, measure the voltage on the 5v pads again- if it’s significantly lower than 5v, you’re likely having an issue with the fc’s 5v regulator. You can bypass that by wiring an external bec to a 5v pad.

If it is glowing brightly, then:
One by one, start reinstalling peripherals, testing with a battery each time to make sure all is well.

Also, make sure that the total amp draw of all peripherals isn’t higher than what the board can handle. (ie: a vtx that draws 1.5A on a board that can only handle 1A [that’s just an example, I didn’t look up the specs of your specific board]).

Edit- also, inspect all boards carefully with a magnifying glass to check for stray solder balls and wire whiskers.

What vtx are you using, and how is it powered? (5v pad, 9/10v pad, vbat?)

VTX is a force vt5804 v2 and is powered by 5v.
My receiver is soldered straight on, but my vtx and camera are just connectors soldered to the board.
Do I need to remove all of them or just the receiver?
Also, is it possible for the bec to be broken already?
Should I try and get it returned and replaced if it is?

Just unplug the connectors, and make sure the pins are straight. Desolder the receiver.

The point of this is to determine if it’s one of the peripherals that is pulling your voltage down, or an issue with the board itself. That’s why I’m suggesting that you reconnect them one at a time, checking via battery power in between.

You can start by just unplugging the vtx and cam, then check for stray solder balls and wire whiskers. Try battery power, see if it properly powers up. Use a multimeter to check what the 5v pad reads. If it doesn’t properly power up, remove your receiver and try again.

If it still doesn’t, and you’ve already checked your esc pins and checked for stray solder balls and wire whiskers, then you know it’s the fc and you can start the return process.

If it powers up with just fine with, for example, just the rx soldered on, but as soon as you add your vtx, it stops powering on all the way- then you know it’s likely a problem with your vtx. Same deal for camera.

It’s possible for the bec to have arrived doa or died on first power up- but because you are getting those second two beeps, it seems more likely to me that it’s something else drawing your voltage down- your vtx, your cam, your rx, or a stray solder ball or wire whisker. That said, I’m often wrong.

It’s also possible that after you’ve unplugged everything and desoldered your rx, it powers up just fine all the way through the process of reinstalling things. If that’s the case, you probably had a stray solder ball that was shorting something that rolled off while you were handling it.

Edit- important side question: you haven’t specified what esc you’re using. Did you confirm that the pin out was the same on harness you used to connect the esc to the fc?

Actually, first things first, try just unplugging the vtx and see if it will power up.

That vtx requires 7v to 24v, and you said you’re powering it off of 5v.

(06-May-2023, 01:44 AM)Lemonyleprosy Wrote: Actually, first things first, try just unplugging the vtx and see if it will power up.

That vtx requires 7v to 24v, and you said you’re powering it off of 5v.

Oh weird, it used to be wired to 5v on my old fc. Thx though, it won't power up with just the receiver and i'm going to desolder it later today when i've got time.

(06-May-2023, 02:21 AM)DrR0x Wrote: Oh weird, it used to be wired to 5v on my old fc. Thx though, it won't power up with just the receiver and i'm going to desolder it later today when i've got time.

Removed all components from my board and will get some desoldering wick later to remove all solder. Still no 5v, 9v or bat power though. Maybe I need to try cleaning with some isopropyl after removing all solder?

Edit- I have checked the ESC pins written on my old flight controller and I think it is the exact opposite of the speedybee pins. Would that cause the voltage drop? And if so how would I go about fixing that?

Cleaning with iso is always a good thing. But if you’re not getting bat, 5v, or 9v power, you’ve got some issues.

Double check the esc harness to make sure the pins are straight on both ends, and that your pin outs match the wiring.

Try plugging a battery in and carefully check the positive wire for voltage, measure on the back part of the jack that the wiring harness plugs into on the fc.

If you’re getting power there, and no signs of life on the board- but the board is lighting up via usb alone, the 5v regulator is officially dead, and hopefully you can get it replaced by the retailer or manufacturer.

I have had a board where I thought the 5v regulator was dead, but it turned out to be the positive pin on the wiring harness jack, it had a cold solder joint that broke off the board- but, that’s a level of troubleshooting you shouldn’t have to do with a new board, especially if you can get it replaced by the retailer/manufacturer.

Just read your edit.

Depending on how it was backward, it could absolutely kill your fc. What was connected to what?

(06-May-2023, 03:26 AM)Lemonyleprosy Wrote: Cleaning with iso is always a good thing. But if you’re not getting bat, 5v, or 9v power, you’ve got some issues.

Double check the esc harness to make sure the pins are straight on both ends, and that your pin outs match the wiring.

Try plugging a battery in and carefully check the positive wire for voltage, measure on the back part of the jack that the wiring harness plugs into on the fc.

If you’re getting power there, and no signs of life on the board- but the board is lighting up via usb alone, the 5v regulator is officially dead, and hopefully you can get it replaced by the retailer or manufacturer.

I have had a board where I thought the 5v regulator was dead, but it turned out to be the positive pin on the wiring harness jack, it had a cold solder joint that broke off the board- but, that’s a level of troubleshooting you shouldn’t have to do with a new board, especially if you can get it replaced by the retailer/manufacturer.

I can't seem to check the voltage on the fc harness jack as it is covered with some form of resin or conformal coating. I have double checked the manual though and have a good feeling the Pinout on my ESC is reversed to the Pinout the fc is expecting. Any ideas on how I could test that?

What brand, model, and version esc do you have?
I or another forum member can tell you what should be connected to what.

Once you’ve verified that the pinout is correct, or changed it to make it correct, if your the fc has a vcc or vbat pad, check it for voltage. Vcc or vbat are going to be (or should be) direct traces to the main positive from harness/esc.

Edit- before anything else, we need to find out if your harness wiring is correct, and if it’s not, how it was wrong- so we know what might now be dead.

Can you also please post a clear picture of your fc and esc, with the cable connected? (Take the fc off the esc, stretch out the wiring a wee bit. I’m trying to see a clear view of the cables going from the esc to the fc

I have took apart my ESC connector and reversed all wires and it now works
Thx for your help lemonyleprosy. Would have already bought a new ESC and fc by now without your help.
Lesson learnt - always check the Pinout even if you think it is correct. I'm lucky I didn't fry the fc.

(06-May-2023, 08:37 AM)DrR0x Wrote: I have took apart my ESC connector and reversed all wires and it now works
Thx for your help lemonyleprosy. Would have already bought a new ESC and fc by now without your help.
Lesson learnt - always check the Pinout even if you think it is correct. I'm lucky I didn't fry the fc.

I’m glad it’s working, and I’m glad it didn’t fry anything. Could have gone very bad.

Happy flying! Oh, and make sure you wire that vtx up to a pad that puts out something in its required voltage range. Double check the paperwork or box it came in to make sure, but everything I found about that vtx said 7v to 24v.

(06-May-2023, 07:16 PM)Lemonyleprosy Wrote: I’m glad it’s working, and I’m glad it didn’t fry anything. Could have gone very bad.

Happy flying! Oh, and make sure you wire that vtx up to a pad that puts out something in its required voltage range. Double check the paperwork or box it came in to make sure, but everything I found about that vtx said 7v to 24v.

Hi Lemonyleprosy,

I have managed to do the exact same thing as DrR0x and reversed my ESC to FC wiring. I am not able to continue testing for a couple weeks but I believe my FC is somewhat fried. When I first plugged in the battery I got 5 beeps and had a couple motors spinning - now when I plug in the battery I only get the first 3 beeps, which indicates the FC is not talking to the ESC.

My wiring is as follows:



I don't have the experience to know exactly what I might have fried, would you have any ideas? I want to try work out how I'm going to fix this in the next couple of weeks - should the FC not work when I correct the connections. I should note that the FC connects to BetaFlight and the accelerometer works correctly.