This model is at end of life, It sounds like a power supply problem. Check power to the unit but I bet it's the internal PSU it seems likely that it has it's own 240v (assume that is supply) or 24v if it is a 24v unit and this will provide the voltages for the electronics It sounds like it is pulsing i.e. there is an overload caused by the circuitry. Most processors will run on 5, +12 & -12 and these supplies are often switch mode with crowbar over current.