Hardware and Power Configuration
Pi Model: Raspberry Pi 4 Model B, 2GB
Power: Powered by a dedicated MeanWell 5V 5A PSU via the GPIO 5V and GND pins (02 and 06).
USB Device 1: Duet2 Controller, running Klipper firmware.
USB Device 2: Fysetc H36 Combo Board, running Klipper firmware.
Both controller boards are powered by a separate 24V PSU that shares a common ground with the Pi's 5V PSU. The USB connections are for data transfer only and either have no VCC line from the start (h36) or their VCC line physically Cut (duet2).
Problem Description
The Raspberry Pi 4 fails to boot when both the Duet 2 and Fysetc H36 boards are connected to the USB ports. This failure occurs on both cold starts and reboots, with no signs of boot activity (e.g., no LED flashes, no HDMI signal).
When this happens neither the rainbow screen is showing up not does the green activity LED show any signs of life at all.
no uart output happens in this case when i set BOOt_UART=1
The boot process succeeds normally if either one of the two USB devices is disconnected. The disconnected device can be plugged back in immediately, and both devices are then recognized and function correctly within the operating system once booted.
Troubleshooting Steps Completed
EEPROM Firmware Verified: The bootloader is confirmed to be the latest version available (May 8 2025) via rpi-eeprom-update.
USB Port Isolation Tested: The failure persists regardless of how the devices are connected to the Pi's USB ports. The result is the same whether they share the same USB controller (e.g., both on USB 2.0) or are split between the USB 2.0 and USB 3.0 controllers.
switched to a MeanWell 5V 5A PSU from the former chineese 5V 3A to make sure its not the PSU acting up, without success.
switched the 24V PSU to a diffrent one i had still laying around to make sure the 24V PSU does not create a ton of EMI that causes this, without success.
Successful Workaround:
The issue is reliably resolved by connecting both or one of the controller boards to the Pi through a dirtcheap simple, unpowered USB 2.0 hub from TRUST. funnily enough, the problem is also solved if i just add the usb hub to the mix as a third device.
![Image]()
anyone has a clue what is causing this strage behaviour and how i can fix the root cause of this without having to put a rather unreliable usb hub into the USB wiring?
Pi Model: Raspberry Pi 4 Model B, 2GB
Power: Powered by a dedicated MeanWell 5V 5A PSU via the GPIO 5V and GND pins (02 and 06).
USB Device 1: Duet2 Controller, running Klipper firmware.
USB Device 2: Fysetc H36 Combo Board, running Klipper firmware.
Both controller boards are powered by a separate 24V PSU that shares a common ground with the Pi's 5V PSU. The USB connections are for data transfer only and either have no VCC line from the start (h36) or their VCC line physically Cut (duet2).
Problem Description
The Raspberry Pi 4 fails to boot when both the Duet 2 and Fysetc H36 boards are connected to the USB ports. This failure occurs on both cold starts and reboots, with no signs of boot activity (e.g., no LED flashes, no HDMI signal).
When this happens neither the rainbow screen is showing up not does the green activity LED show any signs of life at all.
no uart output happens in this case when i set BOOt_UART=1
The boot process succeeds normally if either one of the two USB devices is disconnected. The disconnected device can be plugged back in immediately, and both devices are then recognized and function correctly within the operating system once booted.
Troubleshooting Steps Completed
EEPROM Firmware Verified: The bootloader is confirmed to be the latest version available (May 8 2025) via rpi-eeprom-update.
USB Port Isolation Tested: The failure persists regardless of how the devices are connected to the Pi's USB ports. The result is the same whether they share the same USB controller (e.g., both on USB 2.0) or are split between the USB 2.0 and USB 3.0 controllers.
switched to a MeanWell 5V 5A PSU from the former chineese 5V 3A to make sure its not the PSU acting up, without success.
switched the 24V PSU to a diffrent one i had still laying around to make sure the 24V PSU does not create a ton of EMI that causes this, without success.
Successful Workaround:
The issue is reliably resolved by connecting both or one of the controller boards to the Pi through a dirtcheap simple, unpowered USB 2.0 hub from TRUST. funnily enough, the problem is also solved if i just add the usb hub to the mix as a third device.
anyone has a clue what is causing this strage behaviour and how i can fix the root cause of this without having to put a rather unreliable usb hub into the USB wiring?
Statistics: Posted by Psych0D0g — Mon Aug 25, 2025 3:39 pm