Introduction
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:
- Disassemble the UAP-AC-LITE
- Test if the over voltage protection TVS diode has failed
- Remove and replace the broken diode
What you need
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Tool used on this step:Jimmy$7.95
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The front cover is secured by five tabs.
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Use the Jimmy to create a gap near a clip and insert a plastic prying tool. Apply moderate pressure to force the clips open.
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Tool used on this step:Digital Multimeter$19.99
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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.
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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.
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Tool used on this step:Tweezers$4.99
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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.
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Tool used on this step:Digital Multimeter$19.99
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To install the new diode:
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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.
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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.
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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.
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To reassemble your device, reattach front cover.
To reassemble your device, reattach front cover.
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22 Comments
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.
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.
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.
would be D28 from what I can see above C556
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!
the diode here had 43 Ohms, no matter what direction. (the relativly high value had me ruling out a defective diode in first place.)
Thank you so much! I thought my Ubiquiti UniFi AP-AC-LR was gone, but this simple replacement brought it back to life.
The old AC-LR or the new one? If it’s the new one was it D21 you removed or replaced?
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
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
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.
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.
worked like a charm thanks! have my ac lite running again after plugging it into 48v by accident !
Anyone able to point me to this diode on UAP-AC-IW ?
any know where i can the diode from on my nanohd the diode has 818rg written on it
same question and board, did you figure it out?
Smexhy -
i need repair centre do u know
???
