Hi .
Have something wierd with a few diversity nano receivers on my LR quads/planes. I decided to add a small 1s (managed) backup battery to all of them so i can use find/beacon mode. One works fine but with 2 out of the 3 the RX stays powered on when removing lipo or usb power untill backup bat drained. For the life of me i can not figure out why as all 3 same fw, settings etc. Any bright ideas on why this happens ?
Tried to troubleshoot by disconnecting everything from it (one by one to see if any of the connections to the FC could cause this, but even with everything disconnected , it just stays on. Can manualy switch it between normal and find mode , stays conected fine but does not shut down. On the one that is working correctly it just shuts down immediately when i unplug for example usb after playing with it on the bench. Also when testing with arming etc on the working i get on my TX a message to either shut it down as running on bat power or switch to find mode.
Feels almost like it does not think it is running on bat power while it is for the other 2.
Cant see any difference between the working and non working. Am out of ideas atm

yeah this is indeed a little mistery.. the key here is that you tell your Rx to shut down. when you're done flying and then disconnect your flight battery, CRSF looses link and a red flashing message appears on the OLED, asking you to enter find mode or shut-down. there you MUST select shut down in order to prevent the draining of the backup battery. if you don't pay attention and just switch off your transmitter without your input, the Rx will automatically enter lost/find mode. entering that mode is default unless a shut-down command is received.

using that feature for many years, i've made the experience that it's a mistery when Crossfire is actually asking for the shut-down. very often i unplug my flying battery and nothing happends. i've had days walking by my planes in the hangar and see the Rx slow blinking and i always wondered why.
in addition there is to say, that crossfire did not build any protective LVC or storage mode into that feature. for that reason i've printed my little "black-box" and only use lipos that have 2 connections. with a long long charging cable, i can now connect directly to the backup battery and send it into storage or fully charge at the beginning of the season, check the health of the battery, etc. I had only once case out of 20 where the Rx would drain from that battery and actually feed the FC. this was a faulty Rx. all other 19 Rx's work well but you MUST shut it down manually - always!
it's annoying but still a good feature and i use it on ALL my planes!

P.S. did you know that since a few releases ago, the nano Rx is FINALY (after many tickets to crossfire) supporting the direct connection of a GPS to the nano diversity Rx without their big box, allowing the Rx to send GPS coordinates instead of a beacon even if the flight battery is dead/disconnected. I did not test that yet but it would be a great addition to that feature

Yeah its a mistery. And what you describe is how the 1 that works operates. I can shut down the RX when it asks for it or it shuts down by itself if it has not been armed yet. Or is i shut down TX first and then unplug power on RX it also shuts down. Only after i have armed it starts to intelligently go into beacon mode and or ask for find mode vs shutdown.
The problem is the other 2 do not ask anything, there is no option to shutdown , they just stay working like the lipo or usb is still connected. So not in beacon mode or find mode. Just fully connected and functioning. If i shutdown the TX , the light goes to red but stays like that untill batery dead. If i switch on the TX it connects again like normal.
I can manualy switch it into beacon mode from the TX module and that also works. It just never shuts down.
I suspect (and based on a few tests) that it also does not go into low power mode , but just fully functioning untill bat dies in that state.
all based on comparing behavior with the working one .
Must be some hardware differences between the modules as the working one is brand new, the others a year or so old. But same version written on them (v2.0) and loaded with same firmware etc etc. All identical. Its a big mistery.

I will add a switch between the lipo and the rx to prevent it from draining. At least it has some function on a crash / battery ejection etc although if it does not go into full beacon / power saving mode but stays fully on , it will run out much faster that it should that way. But its at least more than nothing .
All sympoms points to it somehow not detecting its running fully on the backup bat and act accordingly.

Regarding the direct connected GPS , i read about that indeed. But i guess gettong the last GPS coordinates via the FC telemetry is in most crash cases good enough. If eg you loose connection while its flying , the gps still works and keeps updating the last position (eg if it keeps flying for a while before a crash) in the RX so that will be send in beacon mode. After you crash the gps position typicaly does not update (unless you crash on a floating bark in the ocean ;-)
Also connecting you gps not to the FC but to RX only i am not sure how inav navigation would deal with that. You may need 2 gps units in that case. Guess its more intended for if you fly without FC.

p.s. Good idea of a dedicated separate charging/storage cable.

super weird! having 2 out of 3 Rx being faulty?? well nothing is impossible and i had quite a few nano diversity being faulty straight from the factory. maybe about 1 out of 10 had issues. i never had any different behavior of the Rx when arming/disarming or anything else.. that is weird that your Rx detects arming.. did you do something special to get that?
if i understand you right, the 2 problem Rx stay fully powered when you unplug your flying battery and just work off the backup battery until its dead? that would sound like some sort of shortcut on the board. this can't be! that means your backup battery is feeding the FC with power... not good! but it was like this in my faulty one.
this is what i would do on the faulty Rx if not already done:

1) check continuity between plus pole of the backup battery and plus of all pins
2) check backup battery solder connection (it's not that they give you lots of room for it)
3) play around with some FW up/downgrades. I'm still on 4.11 since TBS removed the relay functionality in v6+ and i need that
4) get a RMA from TBS HK and return the two faulty Rx for replacement (might require some tickets before they give you a RMA. but they do eventually if you insist)

when i discovered that i had a faulty Rx, which was working just fine when flying, i had it in a $1k long range jet and i did not want to risk that plane due to a $50 Rx. I asked myself "what else is faulty"... in my opinion it's not worth the risk with such a important component.

as of the direct gps feature i was thinking of putting a 2nd gps module on it. independant of inav and the FC. i had many occasions where the plane flew out of range or dropped out of range, leaving me with the last coordinate when LOS. impossible to find that plane where i fly. so beacon helped a lot once i came into range. it's still a pain finding a plane with beacon mode but better than nothing. some coordinates would've made life much easyer

Thanks for all the feedback and tips. Several i already tried in the last 2 days of troubleshooting this issue.
The funny thing is i used these 2 RX on lots of total send full risk long range flights , zero issues , including realtime mavlink based tracking etc etc.
Zero issues.
But based on all tests sofar there must be something different hardware wise that does not affect anything else, just the backup battery circuitry and related functions i guess. Will do some more intense measuring based of of that circuitry and see if it could explain some of this.
I have a 4th one not tested yet and will see how that one behaves when i get some time .
I did exclude FW software version as all on the same versions of everything as the working one and an upgrade to the latest beta and or full factory resets etc did not change anyting.
Asked TBS on their support ticket system and lets see what they come back with.
May just buy a couple of new as my reasoning is similar to yours and they are in relatively expensive planes/quads.

As Lt Ripley would say.... Just nuke them from orbit, its the only way to be sure.....

yeah I can't see this as any software related issue. must be a shortcut on the board. in all fairness to TBS, that stuff is small and tight and I can confirm that they do have some quality issue in the production. if you find continuity of plus backup battery to plus pins then it's quite clear. if you have a new one, test continuity there as well before soldering so you know for sure.
better to be safe than sorry
good luck!

(01-Feb-2024, 08:09 AM)StuweFPV Wrote: yeah I can't see this as any software related issue. must be a shortcut on the board. in all fairness to TBS, that stuff is small and tight and I can confirm that they do have some quality issue in the production. if you find continuity of plus backup battery to plus pins then it's quite clear. if you have a new one, test continuity there as well before soldering so you know for sure.
better to be safe than sorry
good luck!

Thanks. Yeah i suspect hardware as there is no continuity, but when in that state running of of backup power i can measure about 1.2V between the 5v normal input and ground terminal.
So maybe this leaking from the backup lipo circuit breaks the detection that its running purely on backup lipo. (and why nothing is affected when no backup lipo is used as otherwise its stellar.
Support responded and i send them a video of the issue , so they are on it. Keep you posted.

oh yeah that's suspicious having 1.2V between the two poles. the official working voltage of that Rx is 3.3-8.4V. so i suspect with 1.2V there is some sort of life in the board. on one side good you found the error and got confirmation/proof of faulty and working Rx. on the other side bad as there is no fix for that. TBS support can't do a thing to fix it. the best they can do is give you a RMA and offer you replacement.
In my view still the best Rx out there. hard to beat price, weight, seize and performance. well worth the extra $20 compared to the nano for a second antenna and the option of a backup battery! hope it works out well for you!

After some back and forth with friendly support staff i just RMA'ed them.
Hoping for a fast turnaround...

very good! i hope it works out well and you have more luck with the new RX!

Just a closing update:
I received 2 new chips yesterday and both working fine as expected. So it was indeed a hardware issue .
So takes a bit of patience (EU<>China roundtrips incl customs delays) but very nice and professional RMA process.

(07-Mar-2024, 01:11 PM)fpvapnea Wrote: Just a closing update:
I received 2 new chips yesterday and both working fine as expected. So it was indeed a hardware issue .
So takes a bit of patience (EU<>China roundtrips incl customs delays) but very nice and professional RMA process.

very good! i'd say it was worth the hassle and the wait. now you can go up in the air knowing that your hardware is healthy!