repairing a POE circuit not powering devices but has output voltage - Page 1
Forum section: electronics / repair

author: drakejest
author_rank: Regular Contributor
timestamp: July 14, 2021, 06:24:39 pm
content: So the long story short, i have an NVR that has an 8 port POE for 8 cameras. All of a sudden yesterday all cameras stopped working. After my investigation i have come to the conclusion that the NVR is not able to deliver POE anymore on any of the 8 channels. All other functionalities of the nvr is working fine, even the port still has its ethernet capabilities. I tested it by using a POE injector and the camera powered up and the NVR was able to see the camera. I only have 1 POE injector though and have 8 cameras. I could buy a new NVR but i would like to try to attempt to fix it first before getting a new one.I have very little knowledge of how POE works so i need your help. Having only a digital multi meter makes it hard since from what i have researched there is some sort of handshake that needs to happen first before power is delivered. This is what im trying to figure out if its a component failure or a handshake failure.Upon inspecting the board there seems to be no visible burnt component.There is nothing much on the other side exempt the magnetics for the ethernet, The bottom side is where i think poe is delivered, there is a trace going to the left from the rj45 pins, which appears to be diodes, for tvs or rectification i do not know what i have found out is schematic kinda looks like thisThe port seems to be in pairs, i plugged an ethernet cable and measured each pin voltage to gndPIN | Color | Reading1 S-Green ??2 Green ??3 S-Orange +48v4 Blue +48v5 S-Blue +48v6 Orange +48v7 S-Brown ??8 Brown ??I also read the voltage of the port with a camera attached,- Portx_PIN_A to GND = +47.3V- Portx_PIN_B to GND = +48.0VSo power is really delivered to the camera. Anyone know what might be happening?

author: drakejest
author_rank: Regular Contributor
timestamp: July 14, 2021, 07:27:42 pm
content: Some additonal trace infoim not sure ifIP808ARis the one responsible for turning on power??the physical chip looks like in good condition, anyway i can test if it got burnt ?

author: Pete66
author_rank: Regular Contributor
timestamp: July 14, 2021, 09:33:05 pm
content: IP808AR is POE Controllerdatasheet:https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwjml9e7vuPxAhXYGs0KHfd1BOAQFnoECAYQAA&url=https%3A%2F%2Fdatasheet.lcsc.com%2Flcsc%2F2007202018_IC-Plus-IP808AR_C703550.pdf&usg=AOvVaw08Vwph9RfbynSrajMOVUAGYou have to check diodes, mosfets etc... for shorts. Also look at IC datasheet and check for shorts between power pins and gnd pins. Then remove IC from board and see if short goes away.POE controller chips do go bad. I have 2 Cisco POE switches each having 2 PD69012 POE Controller chips and 1 Trendnet POE switch with a LTC4266 POE chip.In the past 5 years they have all broken and in each case it has been the POE controller IC. I have fixed them all by replacing the POE ICYou can find these on Ali Express but you should buy more than one because sometimes you get used stuff on there.

author: drakejest
author_rank: Regular Contributor
timestamp: July 16, 2021, 08:49:59 am
content: Quote from: Pete66 on July 14, 2021, 09:33:05 pmI found a short on a capacitor. removed all of them , but still there, untill i removed the last one, i thought i was very unlucky, tried to return a different capacitor short returned,I desoldered the IP808AR and the short was gone,what weird is typically if there was a short something would have heated up. but not a sinngle component was hot to the touch.I have ordered the IC on ali as you have recommended as LCSC.com no longer backorders them and digikey doesnt have them.