repairing a POE circuit not powering devices but has output voltage

[drakejest]

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 this






The port seems to be in pairs, i plugged an ethernet cable and measured each pin voltage to gnd

    PIN      |   Color    |  Reading
     1          S-Green      ??
     2          Green        ??
     3          S-Orange     +48v
     4          Blue         +48v
     5          S-Blue       +48v
     6          Orange       +48v
     7          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 = +48.0V



So power is really delivered to the camera. Anyone know what might be happening?

[drakejest]

Some additonal trace info



im not sure if IP808AR is the one responsible for turning on power??

the physical chip looks like in good condition, anyway i can test if it got burnt ?

[Pete66]

IP808AR is POE Controller
datasheet:
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=AOvVaw08Vwph9RfbynSrajMOVUAG

You 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 IC

You can find these on Ali Express but you should buy more than one because sometimes you get used stuff on there.

[drakejest]

IP808AR is POE Controller
datasheet:
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=AOvVaw08Vwph9RfbynSrajMOVUAG

You 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.

I 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.