Steam Deck LCD – Flash MCU, Controller Board “R” Version B (Rensasar RA4E1 MCU – R7FA4E10B2CFM or R7FA4E10D2CFM)
SteamOS cannot detect the controller board; the MCU on the controller board has been replaced and firmware needs to be flashed.
SteamOS cannot detect the controller board. The MCU needs to be replaced and flashed.
There are three options for programming the MCU on the controller board version B.
Option 1: Flash the MCU off the board via external circuitry and then install the MCU onto the controller board.
Option 2: Flash the MCU via an external programmer and tag connection cable (TC2050).
Option 3: Program the MCU to USB boot mode via Steam OS.
You can use the R7FA4E10B2CFM (256 KB flash) or R7FA4E10D2CFM (512 KB flash) MCU on the version B controller board.
Repair Steps
(Optional) Figure 1: Connect the MCU’s Mode pin to ground to switch to USB boot mode for programming.
Option 3: Program the MCU via USB through SteamOS
To program the MCU via USB through SteamOS, we need to switch to desktop mode (e.g., with an external keyboard/mouse) or connect to the Deck from another computer using the recommended method. Refer to other guides if you want to know how to switch to desktop mode or connect via SSH.
Replaced by the “magic button combination” (but very useful for debugging or debugging the controller motherboard firmware): The RA4E1 MCU needs to enter USB/serial boot mode by pulling the Mode pin (MD) to ground during reset/power-on and keeping it down during programming.
Figure 2: Pin arrangement of the Tag Connect (TC2050) interface on the version B controller board.
Step 1 – Prepare the board: Turn off Steam Deck/enter standby mode. Connect the MD (Mode) pin to ground (see Figure 1). You can connect the two pads of the Tag Connect interface (the two in the upper right corner), see Figure 2. Power on the deck/wake from standby. To check if the MCU is booting in USB mode, type `lsusb` in the console. You should see the following device (see Figure 3):
Figure 3: `lsusb`: Hitachi MCU programmed in USB boot mode
Hitachi, Ltd RA USB Boot
Step 2 – Flash the bootloader: Change directory:
Figure 4: Flashing the bootloader on the Hitachi MCU via USB using the script
`cd /usr/share/jupiter_controller_fw_updater/RA_bootloader_updater`
Run the script:
`./rfp_cli_linux.sh boot_ra_Release.srec`
(See Figure 4) The script will prompt you to press and hold the “Right Shoulder Button” (R1), “Upper Right Back Button” (R4), and “Right Quick Access Button” (“…”) (-> “Magic Button Combination,” skip if the MD pin is grounded). Holding down the buttons will begin programming. (The script will power-off and reboot the controller board, and the MCU on the controller board will boot in programming mode if the Magic Button Combination is detected. You can find more information on the Hitachi website.) Press and hold the button until the script prompts you to release. The script will finish, and the bootloader will be flashed into the MCU. Please enter confirmation in the console. You should see a bootloader called lsusbValve Software Steam Controller Bootloader.
Figure 5: lsusb: Valve Software Steam Controller Bootloader
Step 3 – Cleanup: Disable the deck. (If applicable, disconnect the MD and ground wire.) Reassemble the Steam Deck and power on. The MCU will be programmed by SteamOS at startup. Please enter confirmation in the console. You should see a device called “Controller” recognized in game mode. All controller inputs should work correctly. lsusbValve Software Steam Controller
Done.
Note: If you flash a brand new MCU firmware, you may encounter an issue where the Steam Deck serial number and controller serial number are not recognized. Updates via Steam Overlay will not work. Updates via desktop mode work. Other methods are normal. This is likely a pairing issue. I haven’t resolved this yet. Perhaps restoring SteamOS to factory settings or performing a clean install of SteamOS will solve the problem.
