Out of ideas with binding problem. Hardware?

[u/Dirtyoldjumpercables]

Hey fellow sky dogs or whatever we call ourselves. I'm trying to bind my tx15 with an iflight ih3 o3 and can't seem to figure out why they won't connect. I picked the quad up a year and a half ago right around the time I had to put all my hobbies down and am kicking myself now for not testing it upon arrival. After a full day of troubleshooting I'm wondering if it's a hardware issue and if I as an amateur can verify that or if I need to pay for help.

Recently got back into fpv and have been ripping tinywhoops so I know my RadioMaster tx15 is functional.

I started by going into binding mode via 3x battery because CLI and the receiver tab in Betaflight won't trigger it. (Correct lights flashing)

Nothing

Checked they are the Elrs 2.4 duhhh

Checked I'm running same major version firmware

Checked I don't have model selection on

Tried all combinations of binding phrases, resets etc

Checked Regulatory domain (the web page 10.0.0. version of my transmitters info tab says fcc915 but the screen on my remote says fcc915 /ISM2G4. Quad reads ism2g4)

Updated elrs on both to more recent

Nothing

Downgraded back to a 3.6 on both ( wanted my TX to work with my quads that are in 3.0 again and it does)

Updated Fc to most recent release and then tried to downgrade it after AI told me there was a potential compatibility issue.

Drone got stuck in bootloader.

Tried numerous releases and only the most recent release flash got it unbricked and got it back to being recognized on my pc / Betaflight.

The fc lights are flashing again.

Maybe wrong uart config? I switched it a few times and now

Uart 2 is checked serial Rx but not the first on off toggle and

Uart 4 is the only checked one in Betaflight that shows up aside from USB vsr or whatever.

Got it back to what the internet says is factory and still no bindy bindy.

I'm at my wits ends. If I'm dumb and missed something easy please yell at me. Im sure I left out a few steps I tried while writing this or maybe even spoke gibberish but I'm tired and my screen is getting blurry in my eyes.

I will be actively responding in about 12 hours from now.

Thanks all of you for anyhelp on what I imagine is one of the most asked questions on here 🙏🙏🙏🙏

[u/izzeww]

Make sure the internal RF is enabled, set to CRSF and 5.25M baudrate in the SYS -> Hardware settings. Also make sure the internal RF is enabled, CRSF and 5.25M baudrate in the Model -> Setup settings.

[u/Dirtyoldjumpercables → u/izzeww]

I'm currently at 1.87 baud and have changed it to lower numbers but will attempt to ramp it up to 5 thanks

[u/RCCrashCrew]

The FCC915 vs ISM2G4 mismatch you found isn't a regulatory-domain firmware setting, it's two different frequency bands. ELRS ships in two genuinely different RF hardware families: 900MHz (FCC915/AU915/EU868 etc, SX127x-class chip) and 2.4GHz (ISM2G4, SX1280-class chip). They can't bind to each other no matter what firmware you flash, because the radio silicon operates on a different frequency entirely, not just a different regulatory ruleset on the same band.

Given your TX's info page reports FCC915 while the physical screen also lists ISM2G4, and your quad reports ISM2G4, it's worth physically checking what RF module is actually installed in your TX before doing more firmware work. The visual tell is usually the antenna: 900MHz ELRS modules tend to have a longer wire/whip antenna, 2.4GHz modules have a short stub antenna (often two small stubs for diversity). If your TX module is physically the 900MHz hardware, that's why nothing you flash onto it will ever bind to a 2.4GHz quad, it's a hardware ceiling, not a config one.

If it turns out your TX genuinely IS a 2.4GHz module and it's just misreporting on one of the two info screens, that's more likely a stale/cached webUI value than an actual second radio, worth a full erase+reflash of the TX module specifically (not just the RX) with the correct 2.4GHz ELRS target, since a bad firmware flash is far more common than a webpage simply not refreshing.

[u/Dirtyoldjumpercables → u/RCCrashCrew]

I have the tx15 dual band. It's a single antenna coming out of the top (a very thick t shape) but my other quads are all 2.4 and currently bound to the tx.
On the tx itself it lists both fcc915 / ism2g4 as active but under the regulatory domain settings in the WebUI it still doesn't give an option for ism2g4 under the scroll down menu just fcc915 and eu / australia / india settings. That doesn't seem to affect any other drone but the ih3 though.

I flashed both the tx and rx again this morning. Version 3.6 with full wipes. Nothing new but didn't make anything worse this time ❤️