Possible cause 1: The device is not powered on. Diagnosis method: Check the GPIO part according to the development guide and compare the hardware schematic diagram. 1) Check indicator lights: No power to the entire unit → Power module light (PWR) is off; Single module failure → Redundant power supply light is red/off. 2) Measure voltage: Use a multimeter to measure the AC input (220V±10%) and the device power output (-48V/12V, deviation exceeding ±5% is. The signal shows a full signal, but the network speed is still slow? What does it mean when the ONU indicator keeps flashing? Plug in and light up, showing whether ONU is connected to power, ONU without power connection is useless. If it is not a Huawei-certified optical module, replace it with a Huawei-certified optical module. Possible cause 1:. If you find that the Optical/Config/PON Light on your Fibre ONT (Optical Network Terminal) box is flashing, has gone off, or has gone red, this indicates there may be an issue with the fibre connection coming into your property.