Wave disappearing on oscilloscope
As tlfong01 correctly noted in the comments,the scope you are using is a digital storage oscilloscope.
You need to turn on the storage function of your scope.
From page 22 of the manual:

Push the &quot;Storage&quot; button so that it lights up, and you should be able to see the whole trace.
You may need to turn on the available single shot function.  That is described on page 43 of the manual.
Page 42 describes a &quot;ROLL&quot; mode which may also be useful for your signal.  I am not sure from the description how &quot;ROLL&quot; is activated.  It might be automatically turned on at low sweep speeds in storage mode.