I was gifted a unify dream machine 4 port cylinder router with some other unify gear, unfortunately I wasn't the original purchaser so I don't have any idea of how old it is. The gifter said everything worked great when it was packed up but unfortunately upon receiving the hardware everything but the router works well. I have tried to plug the machine in with multiple power cords and tried to hold the reset down while plugging it in. When it is plugged in the fan will do a ¼ turn and then stop. It's almost as though it has a bad capacitor but I'm not really even sure how to open the unit with out any damage and don't want to destroy the beautiful machine. ⁹

⟐ Answered January 31, 2026 at 6:29 MST

Dreading the common PSU problem, I have verified that the PSU is outputting 53V DC and that I can easily draw current from it.

On the mainboard, I have verified that the 24V POE voltage is available on the far end of the board, for all 8 ethernet ports. But on J9, I notice the 3V3 isn't available, which I guess is the main problem. There is no apparent damage to be seen anywhere.

I've been searching the net for schematics and clues as to what might be wrong but found nothing.

Can anyone here help?

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Update:

Thank you Alisha C @flannelist for your nice answer, where you suggest I update the question with some pictures.

The USW8P board looks like this:

On the lower left 53V DC is coming from a tiny but capable 300W PSU.

Lower mid is a connector marked "3V3 R T G" which I presume is for debugging, but people also use it to run a small fan. 3V3 is supply output and G is ground. The function of R and T is unknown.

The 3V3 on this connector is missing.

On the right-hand side of the board are the 24V POE power circuit, where both 53V (input) and 24V (output) are present as expected.

I started tracing backward from the missing 3V3, identifying components on the way, and ended up with this:

The chip closest to the connector with missing 3V3 is an AZO1212, EZBuck 3A Simple Buck Regulator. Its input appears to be cascaded from another chip, the LM5071 Power Over Ethernet PD Controller with Auxiliary Power Interface, where the circuit follows the single Isolated Output application note to a reasonable degree, except for no actual POE supply, only an auxiliary supply):

The big EP13 transformer looks very much like the PA1367NL, and appears to be functioning.

Studying the PCB very closely I discovered a tiny amount of black residue on one side of C2571 and was able to determine that it was short-circuited (zero ohms, also after desoldering) - in the application note this corresponds to one of C7, C8, C9, or C10. With the shorted capacitor removed, the resistance across the remaining capacitors became 1 ohm, which also appears to be way too low for anything healthy.

With power connected to the board again, I measured absolutely no change anywhere.

I'm pretty sure the error exists somewhere in the circuit around the LM5071, but I have no idea how to locate it further. Switchers are pure magic for me.

Any ideas for how I can continue will be highly appreciated.

Also: Happy New Year everyone. :-D

⟐ Commented January 04, 2023 at 5:53 MST