I am trying to use a totally new Keysight 33512B waveform generator. When I connect an external 10 MHz reference signal to the external reference input and set the 10 MHz reference source to "external" via the frontplate controls, an error appears in the upper right corner of the display: "PLL ERR". When comparing the output (e.g. sine wave 10 MHz) of the 33512B to a similar output of another waveform generator (which gets its reference from the same source), the relative phase of the signals is clearly not stable. I checked that the relative phase between the second waveform generator's output and the reference signal is stable.
I use several Agilent/Keysight waveform generators which get their reference from the same source and do not complain. In the manual I couldn't find anything concerning this error. But I guess "PLL" refers to phase-locked loop and the 33512B is not able to lock to the phase of the external reference signal.
Does anyone know how to fix this error?