Hello all. I have been out of the hobby for a few years. I recently got out my quads and got them in the air. Little by little I have been updating components, since we all know how quickly the hobby progresses. This week I upgrade from a BrainFPV RE1 FC swapping it out for the SpeedyBee 405 V3 stack. I'm not getting any input from the radio (the bars on the receiver tab of Betaflight do not reflect any stick movement).
I have a Spektrum FPV Racing sat RX that pre-bound to my DX7 since I couldn't get bind to work in Betaflight (this worked for me when I setup the RE1). The signal wire is connected to the TX2 pad of the FC, the power wire to the 3.3v pad, and ground wire to the ground pad as shown in the manual. I get a solid light on the RX when everything is powered up. I have even tried connecting the signal to RX2 just to give it a try, no luck.
When I flashed the firmware I chose SRXL for the receiver protocol. On the receiver tab I have set serial RX and SRXL from the drop downs. On the ports tab I have serial RX enabled for UART2. I even tried choosing Spektrum for the protocol and reflashing the firmware. I've tried both protocols testing every option available in the receiver tab one by one (Spektrum1024, Spektrum 2048, Spektrum 2048/SRXL, and SRXL) I used this very same DX7 and sat RX when setting up the BrainFPV RE1 on Betaflight 4.4. That setup worked using the Spektrum 1024 option on the receiver tab but doesn't seem to work for me now with the SpeedyBee 405 V3. What could I possibly be missing here? I feel like it is something silly that I have overlooked but I am out of ideas here. Any help would be greatly appreciated. Thanks all.

P.S
Sorry for the long winded description.

Unfortunately the SpeedyBee F405 V3 FC is plagued with a whole load of design flaws (internal serial bus and dma conflicts to name a few), so it could well be that which is preventing your Spektrum receiver from working properly and nothing to do with something that you've done or configured incorrectly. It's difficult to know for sure, but the fact that you say the same configuration works fine on a different FC seems to point the finger at some kind of hardware / resource conflict issue (again) on the SpeedyBee F405 V3 FC.

In the first instance I would temporarily try flashing it back to Betaflight 4.3.2 and/or 4.2.11 where you don't have to worry about setting the right Build Configurations and see if it works fine under those previous versions. If it does, you then know it is either something to do with Betaflight 4.4.x or the Build Configuration options you selected. If it still doesn't work under those previous Betaflight versions then I suggest that it's probably a hardware / resource conflict issue due to the design flaws on that particular FC.

Oh I had no idea there were issues with this board. I did read that there was an issue with using SBUS and the air unit and there being a work around if that was the setup you planned to use. I will try flashing back starting with 4.3.2 and see what happens. I struggle to get this sorted out when I flashed the RE1 with Betaflight 4.4 going from Dronin. Thanks for the suggestion I really appreciate it. I am a bit out of practice and so much has changed since around 2017 when I originally built these quads.

Unfortunately I had no luck reverting the firmware back to earlier versions. Same issue. I am super bummed out that I can't get this going. I have a couple Lemon Rx PPM receivers I will have to try next or buy a Spektrum SPM4650 and see if it makes a difference. If anyone out there is using Spektrum receivers with the SpeedyBee 405 V3 let me know. I really don't want to purchase another new stack.

Update

I thought I would post the route I ended up taking to get my bird in the air. Rather than spend more time fiddling with getting the sat receiver to communicate I simply used a spare Lemon Rx PPM receiver. I pre-bound the rx, soldered the signal wire to the R2 pad as per the manual, flashed the Betaflight firmware adding the PPM segment, and everything functions as it should. Thanks SnowLeopordFPV for bring the hardware conflict possibility to my attention. If not for you I would have continued to beat my head against the wall assuming I had something incorrect with the wiring configuration. It's folks like you that help keep us going rather than just throwing in the towel in frustration. You likely saved me hours. 
So if anyone out there is having the same issue with getting your Spektrum sat to communicate with the SpeedyBee F405 V3, save yourself the aggravation and get yourself a PPM Rx and be done with it. We all want to be in the air and not on the bench.