  A timing system provides high-precision signals to allow the controls over a
variety of hardware and software components in the accelerator complex. This is
guaranteed by the radio frequency (RF) and trigger signal synchronization for
subsystems such as klystrons, pulsed magnets, and beam monitors. The main
trigger signal should be distributed throughout the facility and repeated at
the beam repetition rate. This trigger signal is usually generated by the same
phase of an AC power line to follow the source of the fluctuation of an
electrical grid and reduce the unwanted variation of the beam quality. To
fulfill the needs of the multi-accelerator facility at KEK, apart from the
normal trigger synchronization and bucket selection injection control, a beam
operation scheme called the pulse-to-pulse modulation is utilized; hence, the
complexity of the timing system increases. Uncertainty in the system and a
trigger signal delivery error caused by a drastic AC power line drift are
observed. Further, the effort to establish a reliable timing system at KEK and
several solutions to improve the system robustness are presented.
