Technical Product Manual - DCT1900Maintenance, Fault SignallingMaint-DCT1900/R8/mw 3-5© 2000-2005Fig 3–1 LEDs in the System3.7.1 LEDs on System BoardsEach board has four LEDs at the top. The SLU has two times four LEDs because it consists of aSPU and a CLU on one board, each with its own board controller and board address. The DTUalso has two times four LEDs because it contains a duplication of circuits with two boardcontrollers, each with their own address.LED 1LED 1 is the "board powered" LED, illuminating when the board is powered. On all boards thisgreen LED shall be on.LED 2LED 2 is the "watch–dog reset" LED, illuminating when the board controller receives a watch–dogreset. This LED normally only flashes during the power–on and 24–Hour test when the watch–dogcircuit is being tested.LED 3LED 3 is the "board not polled" LED, illuminating when the board has not been polled by the CPUpoll processor for a period of time. As a result the CPU may not know the board any more, giving itthe state of PNP.LED 4LED 4 is the "error" LED, generally indicating an error on the board. On the CLU, the CLU part ofthe SLU board, and the DTU boards, this LED can be active for other reasons. Therefore, it maynot always be taken as an error indicator.A CLU board or the CLU part of an SLU board will light LED 4 when Base Stations are in NEWstate, which means that a delay value is not yet programmed. The LED will turn off automaticallyafter programming the last Base Station of the CLU or if one Base Station is connected at a time,the LED will turn off when added via CSM.A DTU will light LED 4 when no trunk is connected. The DTU has no error, but the LED indicatesthat no external clock is detected. The LED turns off as soon as a trunk is connected.
