Ubiquiti UniFi AP AC Lite TVS Diode Replacement

Geschrieben von: Yang Zhao
  • Kommentare: 19
Ubiquiti UniFi AP AC Lite TVS Diode Replacement

Schwierigkeitsgrad

Very difficult

Schritte

4

Zeitaufwand

30 Minuten

Einleitung

This guide outlines steps needed to repair an Ubiquiti Unifi AP AC Lite (model UAP-AC-LITE) access point which does not power on, and is identified by the PoE injector having a power fault (blinking white on the PoE injector).

In some cases, affected units' center LEDs may flash dimly when the reset button is held pressed in with the POE power in place. This may only be visible if the board is out of it's chassis.

The UAP-AC-LITE contains an over-voltage protection circuit driven by a unidirectional TVS diode. While this diode is not a fuse, it's expected failure mode is to short, and divert power away from the rest of the board. This short is also detected by the PoE injector, which causes it to not deliver power.

In this guide will show how to:

  1. Disassemble the UAP-AC-LITE
  2. Test if the over voltage protection TVS diode has failed
  3. Remove and replace the broken diode

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    • The front cover is secured by five tabs.

    • Use the Jimmy to create a gap near a clip and insert a plastic prying tool. Apply moderate pressure to force the clips open.

    • Watch out for alignment tabs that may obstruct your progress. Aim to guide the Jimmy toward the center of the front cover.

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    • The TVS diode, marked D6 on the PCB, is located between the antenna and a large IC on the RJ45 port side of the board.

    • It is a 24V uni-directional TVS diode with J leads (SMBJ24A) made by Littlefuse. Note the location of the white bar on the diode, as it indicates its orientation.

    • Use a multimeter or ohmmeter to test whether the diode has shorted. A shorted diode will read less than 1 Ohm in both directions. A working diode will have significantly higher resistance in one direction than the other.

    • If the diode is not shorted, then there may be another issue, and proceeding further may not help resolve the problem with your access point.

    • To desolder the broken diode, apply heat to one side while lifting the diode with tweezers. Repeat on the other side until the diode comes loose.

    • If the solder seems to not want to melt, try using a larger soldering tip to transfer more heat and melt the solder faster.

    • After removing the shorted diode, the access point should power up and function normally. However, omitting this step could result in further damage if an overvoltage event occurs.

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    • Before installing the new diode, use a multimeter or ohmmeter to verify that it is functioning correctly. A working TVS diode will exhibit significantly higher resistance in one direction than the other.

    • To install the new diode:

    • Check the orientation marking on the diode to ensure it is positioned correctly, with the bar pointing toward the antenna.

    • Apply flux to the pads and add a thin layer of solder. If solder does not adhere to the pads, you can add it to the underside of the diode pins instead.

    • Hold the new diode in place using tweezers. While applying downward force, apply heat to one pin near the solder until the solder melts and makes a connection. Repeat with the other lead.

    • Verify that the connections are good. There should be continuity between one pin of D6 and a pin in VR3, and between the other pin of D6 and D7.

Abschluss

To reassemble your device, reattach front cover.

Tinte & Feder

Yang Zhao

Mitglied seit: 01/11/16

825 Reputation

19 Kommentare

Do you think this problem has something to do with Ubiquiti dropping 24V devices altogether? I’ve read about the firmware problems that make 24V passive + POE switch setups a fire hazard, but do you think think this is a design choice or a fix for a flakey on-device power circuit?

Thanks for publishing this, I’ll give it a dead AP I have.

Maxime Rousseau -

Mine broke in exactly the use case warned against here: https://community.ubnt.com/t5/UniFi-Wire.... This kind of failure definitely seems to be linked to the ‘accidental’ 48V activation issue. Unfortunately the device is OOW, but I’ll try to hit up Ubiquiti and see if I can get some good will.

Maxime Rousseau -

Thank you! This fixed my Unifi AC Lite, I plugged it into a PoE switch that fried that diode.

effbees -

Hi, can some help identify the corresponding Diode from this Tutorial on the Unifi UAP-AC-HD? Its POE sections is a little bigger. But didn’t find shorted Diodes. POE LED on Switch is on, but AP not powering on. It boots when 5 V are supplied manually, so somethings is wrong on the poe section.

https://i.imgur.com/WvljJ4T.jpg

It gets warm around the silver elko / capacity next to the transformator. But that’s all what I was able to figure out.

Maya S. -

Good afternoon, if you were so kind to help me identify what the TVS diode is on this Unifi AC HD badge, thank you very much in advance!

https://i.imgur.com/yl9Hmk1.jpg

https://i.imgur.com/KchTfwr.jpg

Roly -

I removed but still no power….any other suggestions?

blindbeck -

the diode here had 43 Ohms, no matter what direction. (the relativly high value had me ruling out a defective diode in first place.)

Andreas Dorfer -

Thank you so much! I thought my Ubiquiti UniFi AP-AC-LR was gone, but this simple replacement brought it back to life.

mojo2600 -

The old AC-LR or the new one? If it’s the new one was it D21 you removed or replaced?

EliteChickenDev89 -

hi i got a UAP outdoor +, the large diode is also open, do you have any replacement for this, UAP+ operates on 48v compared to your which operates om 24v. i wonder if they have schematic diagrams of this Ubiquiti products

James Balagtas -

Thanks, got a “used” AC Lite working.

harryoh -

I have the new AP AC Lite the board is completely different. Which one is the diode.

I have 2 similar diodes D13 and D22.

Please advise

Thank

Alexandros Georgalis -

If im trying to figure out the same power issue on a Unifi AP AC LR, what diodes should I be replacing???

Hector -

do these instructions work on AP AC LR also? I also connected to a 48v before realizing there are two voltages under the same model.

Thomas Gehrmann -

Try making sure you have the correct power supply first. I had the correct V W and A, but it was not “passive, so I thought my device fuse was popped, but when I trie correct V W A with passive, it turned right on.

Thomas Gehrmann -

worked like a charm thanks! have my ac lite running again after plugging it into 48v by accident !

Patrick Mathewson -

Anyone able to point me to this diode on UAP-AC-IW ?

future fear -

any know where i can the diode from on my nanohd the diode has 818rg written on it

Ansar Mehmood -

My UAP AC Lite has another circuit.

What is the culprit diode?

https://i.imgur.com/7uMt6AT.jpg

Mentat -