I've crashed my quad through some trees and it fell at the edge of a lake. I found it sideways with both right motors slightly in water, but everything else was dried. Powered it on and my transmitter (X9d+) connects fine to the receiver but it seems like the FC does not get any signals from the receiver. I took it home, plugged in into PC and confirmed my suspicion, FC thinks that there is no transmitter but my Taranis connects fine to the R-XSR with maximum RSSI strength. Took it a bit apart, all the LED on the receiver seems fine, all the cables are connected properly to the FC, there is no obvious problem. Is there anything else I can do before I order a new receiver? Can it be the FC?

Is there a blue LED on the R-XSR as well as the green LED when your transmitter is powered on? If not then your R-XSR has somehow switched over to CPPM mode. To switch it back you need to hold the bind button on it for 4 seconds until the blue LED flashed 3 times. Then power cycle the receiver.

If that isn't the issue then check your Betaflight Configuration settings. It's not been unknown for the configuration to reset itself to back to defaults in the event of a power issue.

Yes, there is the blue LED as well as the green so it's not in CPPM mode. I have also checked (again) in Betaflight Configuration settings and I can't see anything wrong. Everything is as it was before. I am going to desolder and resolder the SBUS wire and see if that makes a difference, even though I can't see anything wrong with the connection.

UPDATE: Redone the wiring and also checked with a multimeter that there is a connection between FC pads and receiver pads. Not sure if I should just order a new receiver.

It's difficult to say what the problem might be. You could have fried the UART that the receiver communicates through. Roll the dice. The cheapest item to get a replacement of is the receiver so that is probably the obvious thing to go for. Even if it turns out not to be the receiver then it's always handy to have a spare receiver in your spare parts bin, so it won't be a wasted purchase.

Why not try a different UART?

(07-Apr-2020, 06:00 PM)Birbal Wrote: Yes, there is the blue LED as well as the green so it's not in CPPM mode. I have also checked (again) in Betaflight Configuration settings and I can't see anything wrong. Everything is as it was before. I am going to desolder and resolder the SBUS wire and see if that makes a difference, even though I can't see anything wrong with the connection.

UPDATE: Redone the wiring and also checked with a multimeter that there is a connection between FC pads and receiver pads. Not sure if I should just order a new receiver.

It may be like they said a UART....... If you happen to have another that isn't being used it's worth a shot like Voodoo said.. What did you find with the multimeter? Did the 5V pad give the appropriate voltage?

Update: I have tried different UART and also bought a brand new receiver but still no luck at all. Measured with the multimeter the voltage on the receiver and is 5.13V steady. I am getting mad and running out of ideas.

Have you tried a complete erase and reflash of the firmware?

(16-Apr-2020, 07:08 PM)Birbal Wrote: Update: I have tried different UART and also bought a brand new receiver but still no luck at all. Measured with the multimeter the voltage on the receiver and is 5.13V steady. I am getting mad and running out of ideas.

You should check the voltages on the flight controller as well just in case. It wouldn't make sense that it's the issue with the flight controller given your description. But your issue not being resolved doesn't make much sense as it is... it's weird, it doesn't seem like there should be anything stopping you from connecting but something is.....

(16-Apr-2020, 08:45 PM)bLoWsMokE Wrote: You should check the voltages on the flight controller as well just in case. It wouldn't make sense that it's the issue with the flight controller given your description. But your issue not being resolved doesn't make much sense as it is... it's weird, it doesn't seem like there should be anything stopping you from connecting but something is.....

I did everything and nothing worked (even full erase and reflash the firmware as the previous post suggested). I gave up and just ordered a new FC...it will be the 3rd one I go through in 5 months since I've started FPV 

So in conclusion, old RX + new FC = problem solved. I keep wondering what happened to that FC that it won't read any SBUS signals  . Apart from this everything seems to work on that FC, camera, VTX so the UARTs are functional...ESC is responding normally, etc.

it is odd that all you Uarts are not working.

(22-Apr-2020, 03:11 PM)voodoo614 Wrote: it is odd that all you Uarts are not working.

UART is also the microUSB connector as well that I plug in into PC with BetaFlight. That is working...so I think UARTs are fine but for some reason does not read the SBUS protocol from the RX. Anyway when I get some more time, I'll play more with that old FC to see if I can still use it.