The very first time you update a MPM without the bootloader it has to be done in this manner if direct connect fails.
If the bootloader is installed then one can update directly from the TX. I'll follow up on this soon.
I had almost no problem updating the IrangeX.
Opened the case (2 screws). Be careful removing the board as to not damage antenna connection. I left mine plugged in as removal and replacement is not a good idea. Also take note which way the antenna cable loops back into the case.
I added, by soldering the 4 pin header to the Gnd, Tx, Rx, Vcc.
I used a short piece of wire to jumper Boot0 to 3.3V and soldered it too.
I connected and FTDI serial ttl converter at 3.3v gnd to gnd, Tx to RX, and Rx to Tx.
https://www.ebay.com/itm/3-3V-5V-FTD...o/382655837965
Downloaded and installed flash-multi from here:
https://github.com/benlye/flash-multi
follow the instructions to load drivers.
Flash-multi,exe is the application file to run.
I plugged the ftdi in the USB serial port.
From my windows machine I found, via device manager, usb serial on com7 so I set the flash-multi to com7.
I downloaded the firmware file from the link in flash-multi. I used: multi-stm-opentx-aetr-inv-v1.2.1.85.bin
aetr is the default for the MPM. It will reroute TAER to DSM selection automatically. Many have problems when not doing this. If you choose a different default you will have to set the Transmitting controller and install the same defaulted channel firmware.
After carefully connecting the out of case MPM to the transmitter, and made sure the 2 wires were going from the MPM to the FTDI I applied power to the TX. browsed to add the firmware I just downloaded I pressed upload on the flash-multi.
It takes a minute or so to complete.
When done successfully I shut down all and disconnected.
I removed the MPM, cut the Boot0 jumper, re-assembled the module and I was done.
When you select the setting EXT RF to MULTI and whatever protocol you will see the new version under status.