I have a Vorsetzer Pianocorder with the original owners manual.  In the
manual it explains that the light goes out as the tape plays, but comes
back on as the tape comes to the end of the selection.

My service man explained to me that it also comes on between notes.
Watch and see if the light coincides with note changes.  This might
explain your problem.  I was told that this is normal for them.  Mine
does not seem to drop notes as the book explains so I haven't been
concerned.  Hope this helps.

Dave Brown