Help with board not booting from PoE

TLDR: Two boards, one won’t boot from PoE, definitely the mainboard (or software) that is the problem, can anyone help me debug?

Hi, I have two identical setups:

RockPi4C
NVMe (Acer 128GB from Allnet)
RockPi PoE hat

Both booting from NVMe, from the same build (Debian 9) using the same guides. Both are connected to the same switch (Unifi 8 port 60w), using the same two sockets (have swapped both to eliminate anything to do with the switch). Switch shows <4w for the running board, and there are no other PoE devices connected.

One board will not boot from PoE alone, requiring USB power instead, I just get a green flashing light when using the PoE alone (according to @jack previously, this indicates that not enough power is reaching the board, or that the supply is irregular).

I have swapped the PoE hats, and the same situation holds - the same RPI does not boot, so I know that the hats are fine.

Can anyone help me with the next steps in debugging? I am running fairly simple packages at the moment, but I’m now going through comparing these to each other in the hope that I find something that looks different.

Do you have multimeter? Can you measure the voltage of GPIO PIN 2 when powering only from the PoE. To power the board from PoE, no software is required.

Do you have multimeter

yes, so I put black to Pin6, red to Pin 2, range to 20v:

I get a pulse every ~1 second. Half the time it peaks at between 3v & 4v, half the time it peaks at 1.5v

Having the same problem here. Currently looking for my multimeter. Board gives flashing green light of of USW-8 and it gives the same thing when using a spare unifi POE adapter I have from the device that’s plugged into the USW-8 port. Adapter is exact spec the board calls for. Tried this with two nvme’s and two os’s.

Cheers @bradlees, @radxa any ideas on next steps please? Considering this is the 5v rail, I’m assuming that the board is not getting enough voltage quickly enough to recognise, and so not allowing the boot to happen.

Is this classed as a manufacturing defect? Are there any other steps I can take to check the board over? You can probably tell that I’m not an electrician… but I’ll happily electricute anything you tell me to

This seems a shortcut of the board makes the PoE reset. Can you check:

  1. power the board from USB C, is the ROCK Pi working fine? Measure the voltage of PIN2/6. Without the PoE HAT at all.

  2. do you have dupang cable? If yes, you can use 4P dupan cable connect the PoE header and PoE HAT, another 2P connects 5V from the PoE HAT to PIN2/6 of ROCK Pi 4, ie not connect all 40P. Be Careful with the pin, make sure not insert the wrong ones.

  1. power the board from USB C, is the ROCK Pi working fine? Measure the voltage of PIN2/6. Without the PoE HAT at all.

Board works fine with USB C.
Voltage with PoE HAT (not using PoE port) 4.8v
Voltage without PoE HAT: 4.8v max, but fluctuates much lower

  1. do you have dupang cable? If yes, you can use 4P dupan cable connect the PoE header and PoE HAT, another 2P connects 5V from the PoE HAT to PIN2/6 of ROCK Pi 4, ie not connect all 40P. Be Careful with the pin, make sure not insert the wrong ones.

Excuse the messy desk:

I get the same result, green light flashes every ~1s, no boot. Voltage pulses to 4v sometimes, usually between 2 & 3v, then back down to 0.

1 Like

Hi @radxa or @jack, is there anything further I can do to get this moving?

Thanks for the picture and measurements. We are on the holiday now. We will look into this issue after the holiday(8th, Oct).

Hi @radxa, sorry I left this so long got very busy over here! However, wondering if you can give me any next steps or ways to investigate? I can boot the board from USB, just not from PoE alone.

Thanks,
Alex