Fixed – Inverter Mod for TBS Crossfire and FrSKY QX7, X10S & X12

The current hardware revision of FrSKY QX7, X10S & X12 is not fully compatible with the TBS Crossfire protocol.
If you get constant telemetry warnings or your LUA Script is not working, you might be affected. The reason is a wrong (changed) inverter on the FrSky QX7, X10S & X12 wich can not handle the 400k baudrate of the CRSF protocol.
Your Radio Link to the aircraft is not affected, just the telemetry or LUA Script.

Solution 1: Software fix

You can set the Baudrate to 115200 and your Crossfire Module will work without any issues.
Be aware: The lower baudrate will slow down the CRSF protocol

This workaround will give you a baudrate selection on your X7 menu (main menu, hardare page). If you lower it to 115’200baud instead of using 400’000baud the issue is resolved. Due this workaround and the lower baudrate the latency will increase. The regular update rate for CRSF between OpenTX and Crossfire is 250Hz (4ms). Using the lower baudrate the update rate is reduced to 62.5Hz (16ms). Because of this we recommend to fix it properly in hardware if you have the soldering skills or ask FrSky for support on fixing the hardware.

  1. Download latest Taranis Firmware
  2. copy the firmware onto the SD Card into the „FIRMWARE“ folder
  3. start the Taranis in bootloader mode
  4. flash firmware and select 115200
  5. Go Fly!


Solution 2: Hardware fix

I created the following PCB wich TBS and many online shops now sell. With this mod, you can get the full 400k baudrate for your TBS Crossfire System.
You can get this Inverter via TBS or for example the german FPV Racing Online Store
Warning: Only do the hardware mod if you know what you are doing. To desolder SMD components you need a bit of tact. The components around it can be damaged very easily if you don’t do it correctly. Please make these modifications only on your own responsibility/risk. Neither TBS, FrSky or I can guarantee that the mod works! Thank you!

Please follow the guide below:

Mod for FrSKY Taranis QX7

Mod for FrSKY Horus X10S

Thanks Yann Bouloiseau for the photos and information for this mod!


Mod für FrSKY Horus X12

Thanks to stxShadow for the Mod – Thanks to for the photo of the PCB


SMD Part List

If you accidently desoldered some nearby SMD parts, don’t worry. I grabbed an old mainboard, desoldered and measured some parts.
Here is a List of parts:

FrSKY Taranis QX7

  • Q400 9014 Transistor
  • R406 10k Ω
  • R407 10k Ω
  • R402 4,7k Ω
  • R415 54 Ω
  • R413 10k Ω
  • R104 1M Ω
  • R106 10k Ω

FrSKY Horus X10

  • no data available yet (if you have a broken mainboard, please send it to me)

FrSKY Horus X12

  • no data available yet (if you have a broken mainboard, please send it to me)
Wenn dir dieser Artikel gefallen hat und du mich unterstützen möchtest, findest du hier drei Möglichkeiten. DANKE!

Auf Patreon findest du auch weitere Infos zu meiner Person und dem Blog


36 Antworten

  1. Kurt sagt:

    Hat jemand auch das Problem bei der Taranis XD9+ .Der TBS Crossfire Micro Transmitter scheint keine Verbindung zu meiner Taranis X9D+ aufzubauen. Crossfire Meldung „Waiting for crossfire devices…“. Auf dem Display erscheint Running aber no RC Signal.
    Scheint das gleiche Problem wie mit der QX7 zu sein?

    Habe alles versucht, wirklich alles.
    Meine Graupner MX20 funktioniert über das DSC Cable (PPM).

    Bitte um Hilfe.
    Vielen Dank

  2. Stefan sagt:

    Hi Phil,
    great work. Will be any High Speed 7404 inverter works well or there is any special requirement? Thank you for your work for FPV community!

  3. tplanefpv sagt:

    Hi Phil – i was doing the mod, and removed q400 from QX7. while soldering wire onto the pad where q400 previously was, that pad came off. Anything I can do to save this taranis? thanks in advance


    • Phil sagt:

      Hey tplanefpv,

      sorry to hear. You can try to locate the wire which was going to the pad and scratch the silkscreen off now grab a very tiny wire and solder it ontop.

      Hopefully you can repair it, please report back!


      • tplanefpv sagt:

        Think I was able to fix it by scraping some of the green stuff and soldering onto the copper! charging some batts to try this it out!

        Hey, another question – i did the software fix first. But at a slight distance, i would keep getting warnings „telemetry lost/ found “ and „rf signal critical/low“ – was that expected? literally 100 feet away with Baudrate to 115200


  4. dutzi sagt:

    Hey Phil
    I Hope you are able to help me. I just tried to do the Mod on my X12S and in a weak moment desoldered and disapeared R128…
    Do you by any chance now the resistance?
    Thanks in advance and greetings

    • Phil sagt:

      Hey Dutzi,

      sorry to hear, but i cant help you. I dont have one here. Please ask FrSky Customer Support, they share those infos. I organized a broken QX7 Mainboard to measure all resistors and share it with you! When you get the Resistor Value, please share it here!


  5. Radu sagt:

    Hello! Did everything according to the instructions. But that “before”, that “after” setting the mod at 115k CF is working, but with 400k there. Prompt please where to dig? Hardware X10S. Thank you!

  6. Matt Howard sagt:

    Hi, Thanks for fast reply. I am currently soldered the output to the other pad of Q400 and it seems to work however I have not tested out range yet and I am still unable to get into the crossfire lua script. Just stuck on Waiting for crossfire. I will try find the trace and solder to that and hopefully that will fix my lua script aswell. Otherwise I am officially stuck 🙁 Thanks for helping phil

  7. Matt Howard sagt:

    Hi Phil, I recently did the inverter mod however while I was desoldering the old Q400 inverter and the pad came off. Does it matter if I solder the output to one of the other pads that was used on the old Q400?

    • Phil sagt:

      Hi Matt,

      that’s bad to hear. Did the pad come off, where you connect the inverter? If so, you can’t connect it to the other pads.

      Here is the solution. Follow the trace of the lifted pad. With a sharp Skalpell, cratch the silkscreen (green paint) off the trace untill you see the copper. Scatch as much as you can but keep away from other parts. Apply some solder and solder it to the scratched trace.

      Hopefully that will work. Report back if you like!


  8. Jason Baldridge sagt:

    Hi Phil, I am having an issue that I am hoping you can help me on…I installed the chip for the baud rate problem and ever since then my ‚discover sensors‘ feature no longer works, plus when I try to run the crossfire lua, for some reason it just flashes ’searching for crossfire devices‘ but never locks on to anything…I should of tried crossfire before doing the mod to rule out something going wrong, but I didn’t…There is no telemetry working on the TX; no Lua’s, no sensors being detected; do you know what is going on? In the link you will see that my X10S is different than yours; mine has no watch battery on the back and yours does for some reason..?….I really need help getting this resolved; do you know what part Q1 was so that I can order 1 to install to see if that fixes my issue? Any help would be great; thanks!

    • Phil sagt:

      Hey Jason,

      sorry for the late reply. I hope you got it solved. Indeed, it would be better to test the Crossfire before doing the mod. Anyway, how did you configured the LUA Script, FC and all the stuff around the Taranis. There could be manny points where it can fail. I don’t think it has something to do with the inverter Mod (at least you did not desoldered some other parts from the pcb by accident).


  9. Mitch sagt:

    Hi Philipp, thanks for your work. Do you have part schematics so I can make my own mod? I cant find local retailer of your mod.


  10. clifyb sagt:

    Hi Phil, I didn’t realize I had the older QX7 and went ahead and did the mod you listed above and i doesn’t work. I later read the „S“ pin on the lower sPort is not functional on the older QX7 radios so I seem to have disabled sPort on the rear bay port pins too. Can I recover this by wiring the „In“ wire to one of the pads at the Q400 location? Thanks

    • clifyb sagt:

      Update: I recovered from my unneeded Q400 mod on my early QX7 by moving the ‚In‘ wire from the non-functional „S“ pin on the sPort per your official mod; and moving it to the Q400 transistor pad farthest from the „Q400“ label. Now it flashes my Rx’s just fine from the rear bay port pins like the X9 and I’m using the latest part from your cool mod PCB too, so Crossfire works fine too.

  11. Yi Joe sagt:

    hi umm i am new and can i ask you a question? will i hard the q x7 if i remove the part q400 with a hot air gun? will it be too hot?

    • Phil sagt:

      Hi Yi Joe,

      if you are not familiar with hot air desoldering please be carful. Grab an old pcb and practice a little.

      The other way, would be with a tiny soldering tip. First lift the one leg and then heat up both legs together on the other side to remove the component.

      But be careful with all the smd components around the Q400. There is at least one person i know who messed up the board, because the accidentally damaged some other parts on the PCB.


  12. GBaquero sagt:

    The X7S has that problem too?

  13. Jure Peternel sagt:

    Hi, am I missing something: why would I need this mod for use with TBS MicroTX? I have this setup and I’m flying without a problem :/

    How are the errors demonstrated? How can I check if I have a problem? Thanks

    • Phil sagt:

      Hi Jure,

      not all Radios are affected. Some older batches seems to work without the hardware mod (like my Q X7). But the most Q X7 and X10/S have this failure.

      Errors will be constant telemetry warning and crashing LUA Scripts.

      If it works on your Radio, your are very lucky and don’t have to change anything. But be shure you run it on 400k Baudrate. 😉


  14. the_mazur sagt:

    After „Hardware fix“ in menu need back Max bauds to 400000?

  1. 26. November 2017

    […] Vorheriger Beitrag Fixed – Inverter Mod for TBS Crossfire and FrSKY QX7 […]

  2. 2. September 2018

    […] подробно описано – на разные аппы. У меня получилось […]

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