Abstract: A vertical phase adjust circuit with high noise immunity for line locked surveillance cameras. To prevent noise from the AC line producing false output signals, a counter is used to lock out the delayed vertical line locked output signal. The horizontal scan frequency is counted from the time a vertical output is produced, and the vertical output signal is prevented until 98 percent of the period between legitimate vertical signals has elapsed. The circuit also includes a lock detect circuit to increase the time window during startup conditions to assure initial synchronization and an increased phase adjust range to permit synchronization with any other camera.