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Electronic Theatre Controls Inc

CEM3 Front Ethernet Port Problems


If the following are true:

  • Power-over-Ethernet works
  • Data does not work
  • Ethernet jack right green LED is OFF with an Ethernet device plugged into the port
  • LD8 and LD11 on the PCB are OFF with an Ethernet device plugged into the port

Likely problem is with the Ethernet jack

If the following are true:

  • Power-over-Ethernet does not work
  • Data does work
  • LD15 is OFF

Likely problem is somewhere on the +48V rail

Explanation of Issue

Ethernet jack problems will appear as functional PoE, but no data. This can be confirmed by looking at both the PCB while it is on and the front Ethernet jack. The jack should normally have the right LED be on when plugged in to a device and LD8 and LD11 will be on (both red, located behind the LCD, above U60).
If a cable is plugged into the front Ethernet jack, is powering something with PoE, and those three LEDs are off, then the jack is the likely failure point. The Ethernet jack has several components built-in that cannot be replaced, so the Ethernet jack must be replaced.


Power-over-Ethernet voltage test points are located near some components at mains voltage. Use caution when taking measurements

PoE problems are likely a problem with the +48V rail and can be confirmed by checking LD15. This is the LED indication for the presence of the +48V rail that feeds the PoE circuitry.

Alternatively, the +48V rail can be measured by checking the voltage at the +48V test point. Use nearby L7 as the ground reference as the +48V ground rail is isolated from the two ground test points on the board.

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