PoE Switch Port Repair - Page 1
Forum section: electronics / repair

author: Nav
author_rank: Newbie
timestamp: March 27, 2025, 03:14:41 pm
content: I want to start off by saying that I am a complete novice to PCB repair, but have done the basics on a PCB if it was simple soldering or quick cap replacement. I'll keep it detailed as possible that way I can get led down the right path to find out the problem. I have a Ubiquiti/UniFi 24 PoE network switch which seems to have to bad/dead ports.... all details listed below, and link to pictures attached below.https://imgur.com/a/qt9es2HObservations- Ports 7/8 are able to get 802.3bt power confirmed power by orange light on the port, and SSH into the switch looking at port status showing 10W being supplied to the camera, but no data link at all.- Port 7 gets a data link when a laptop is plugged, but won't do PoE/data together when either a PoE camera or access point is plugged. The port won't auto-negotiate past 100mb (FE). I confirmed that the laptop was getting full 1 gigabit on every port.- Port 8 only gets PoE power data does not work at all when testing with laptop or other devices.- Nearby ports like 9/10, and 5/6 work without any issues. I'm assuming since it's a 24 port switch all jacks are paired up with some type of chipset.Troubleshooting Performed- Checked PCB for any blown caps or anything that seemed burnt- Tested are cables to rule out a cable issues, and even grabbed some new ones. Multiple types of devices tested on those ports to also rule out any device problems.Not sure how this whole PCB works, and what exact type of components are required for a PoE switch to work, but from basic knowledge seems like some type of chip that does the negotiation or the PoE port is bad as it will not got past 100mb on Port 7, but it does provide full 802.3bt power. Port 8 only does power, but no data.. Hopefully someone can lead me down the right path as I've gone down the rabbit hold on this ,and would love to learn what is causing it/how to fix it.

author: pcprogrammer
author_rank: Super Contributor
timestamp: March 27, 2025, 03:38:23 pm
content: No expert, but do know some about the subject.Your pictures show a separate board on top of the main board. This is the power injector board. I assume the RTL8239 to be a POE supply controller, but can't find a datasheet for it.The main board has a long row of transformers to galvanically separate the external wires from the internal ethernet logic. What you can try is to run the switch without the power injector board and see if all the ports work as expected without delivering POE of course.If port 8 works normally with your laptop in this case, the fault most likely lies in the power injector board. That will be a lot harder to investigate without a datasheet.

author: Nav
author_rank: Newbie
timestamp: March 27, 2025, 05:40:23 pm
content: I'll give that a try, and report back. I also looked for the datasheet on the RTL8239 but had no luck finding any info.

author: pcprogrammer
author_rank: Super Contributor
timestamp: March 27, 2025, 05:42:50 pm
content: Realtek is not really forth coming with datasheets on these types of chips.

author: Nav
author_rank: Newbie
timestamp: March 27, 2025, 06:10:25 pm
content: Quote from: pcprogrammer on March 27, 2025, 03:38:23 pmI just tested it without the PoE injector board. Port 7 links at 100mb, and port 8 gets no link at all. I checked all the other ports, and was able to get a instant link at 1 Gig. I did notice that port 7 took a little longer than to get the green up link light compared to the rest. I guess that rules out the power injector board as the issue persist without it connected.

author: pcprogrammer
author_rank: Super Contributor
timestamp: March 27, 2025, 07:41:52 pm
content: Quote from: Nav on March 27, 2025, 06:10:25 pmYes, now you know it is in the main board somewhere. With it being a multi layer board, judged on the photos of both sides, and the ethernet phy's most likely being in those marvel ic's, you are in a pickle. It could be the transformer for those ports. There are 12 of those big black parts on the PCB, so two ports per package. For gigabit ehternet all 8 pins of the socket are used, but for 100 megabit only 4 pins are used. This could mean that only part of the transformer setup is dead.Post a close up of one of those parts to see what the markings are on top of them. You might be in luck and it is solvable by replacing such a part.

author: Nav
author_rank: Newbie
timestamp: March 27, 2025, 08:15:17 pm
content: Quote from: pcprogrammer on March 27, 2025, 07:41:52 pmHere is a closer picture. I didn't find anything when looking up FPE LK48223SN 2439J, so thinking it may have been a custom part.https://imgur.com/a/uQ56dbT

author: pcprogrammer
author_rank: Super Contributor
timestamp: March 28, 2025, 06:54:54 am
content: Well my knowledge ends here. Without knowing the transformer configuration you can't do much.Maybe you can try to contact Ubiquiti for more information under the right to repair movement.