The PFG amplifier offset drift over time, with noticeable effects even one month after adjustment.

Load a lineshape sample and the global/All Files/cosy_pfg.jxp pulse sequence.

In the interactive pulse tab set shim and set lock gain so the lock signal is about 2000.

Open the cosy pulse sequence parameters
In the [Pulse] tab Change the grad_1_amp value to 0[mT/m].
In the header tab add [repeat] from the [Add Parameter] and set to on
In The[Acquisition] tab set scans=1 and x_prescans=0
Close the experiment parameters settings.

See attached image.

While observing the lock signal adjust the OFFSET at the front of the FG AMP UNIT to the maximum lock signal.