Jupyter Notebook - font issue

I have a jupyter notebook running in PyCharm CE 2017.1.2. When I display a pandas dataframe in the notebook the font used is a bizarre cursive script that is very difficult to read. All the other cell contents are displayed OK. If I point a browser at the Notebook IP address, the table display font is normal. How can I fix this ? None of the font setting in Preferences have any effect.

Thanks.