Ubiquiti US-8-150W schematic diagram

[Pr0metheus]

Hello guys,

I am repairing an US-8-150W PoE switch, and cannot find schematic diagram anywhere. Or at least, I need to find values of burned resistors R2219 (?) and R2408/R2409 (probably 10 Ohms ?). Anyone here who is willing to measure theese componentts directly from the board?

Thanks

[CapLeaker]

1R0 is 1 Ohm. Not 10 Ohms. 10 ohms would be way too high. Whatever goes there it’s a low ohm resistance that goes there to GND. Something like 0.1 to 0.5 Ohm effective. So two 1 ohm in parallel = 0.5 ohm. Sound correct to me.

[Pr0metheus]

Who said 1R0? Not me. I don't know value of theese resistors, was just guessing. They were completely burned, so no labels visible.

[stj]

1R0 was in the second picture and is probably a similar circuit.
did you find out what overloaded and burned them?

[Pr0metheus]

There was overvoltage from the PSU (70V) feeding the board, which resulted in destroying two input mosfets (1st pic) together with resistors. They could be theoretically 1R0, feeding the Mosfet source. But in the 2nd pic, I don't know the value of this micro resistor R2219.
Maybe @CapLeaker could help with indetification?

[CapLeaker]

Where dos this little resistor connect to? Maybe find another similar circuit on that board or find another unit and measure it. Unfortunately I don’t think these are marked. Could be anything from a resistor down to a jumper. What is the resistance of it?

[Pr0metheus]

You have posted picture of that mainboard, so I suppose it was your unit. If not, I will measure further.

[apholabi]

Technical Analysis: Resistor R2219 (Ubiquiti US-8-150W)


In the Ubiquiti UniFi US-8-150W switch, the resistor identified as R2219 is located in the power section, specifically near the FDP2572 MOSFETs (usually within the PoE delivery stage or the internal power supply unit).

• Standard Value: If this resistor is connected directly to Pin 1 (Gate) of the FDP2572, its typical value is 10Ω (10 Ohms) or 47Ω (47 Ohms). These are typically SMD components (often in 0805 or 0603 packages).
• Function: It acts as a Gate Resistor. Its purpose is to limit the switching current to the Gate and dampen high-frequency oscillations (ringing) that could damage the MOSFET or the controller.

Why does it fail?


If you found R2219 charred or "blown" along with the FDP2572, it is almost certain that the MOSFET suffered a Drain-to-Gate short circuit. When the MOSFET fails this way, the high voltage from the Drain rushes back into the low-voltage control circuit, instantly destroying the gate resistor. Repair Recommendations:

1. Don't just replace the resistor: If R2219 is damaged, the FDP2572 MOSFET is definitely dead and must be replaced.
2. Check the Gate Driver: Often, the voltage spike that kills the resistor travels further back and destroys the PWM Controller or the Gate Driver IC. If the switch doesn't boot after replacing the MOSFET and resistor, the driver chip is likely faulty.
3. Value Verification: If the resistor is too carbonized to read its code (e.g., "100" for 10Ω or "470" for 47Ω), check the surrounding PoE channels. Since the US-8-150W has a repetitive layout for its ports, you will find an identical "twin" resistor nearby to confirm the value.

Pro Tip: If the failure is within the internal power module (often a G0688-150W), be extremely careful with high-voltage capacitors. Many technicians opt to replace the entire internal PSU with a Mean Well EPP-150-48, which is a highly reliable and compatible alternative for this specific Ubiquiti model.

[apholabi]

Resistor R2219 is most likely 10 ohms also check diode D250 it could be shorted.