Can anyone help me with a problem I have?

I have a sheet which is divided into 4 quadrants, two contain data tables,
and two contain charts (1 line, 1 bar).
When I print the sheet, or print preview it sometimes the charts are shrunk
to approx 25% of their normal height, although the width remains the same. It
does it mostly on the Bar chart, but sometime on the line chart, some times
on neither, and sometimes on both!

I'm pulling what little hair I have out so if anyone can shed any light on
this then I'd be grateful.

Thanks

Neil