Hi Toril,
The reset that is carried out if you hold down the rightmost key (C6) whilst turning on the power only resets the 'System Setup' parameters.
There is a note in the section 'Resetting to the Factory-programmed Settings' on page 32 of the PSR-S970 Owner's Manual which refers to resets carried out by the above procedure which says:
NOTE
The recorded Songs (page 68), Expansion Packs (page 46), and other files
saved to this instrument are not deleted by this operation.
As Michael said, the Setup parameters that are reset are shown in the 'Parameter Chart' in the downloadable 'PSR-S970 Data List'.
They appear with an 'O' in the column headed 'Setup' in the 'System' group of columns.
The leftmost column in the chart lists the Parameter, then there are 2 columns showing which keyboard model (S970 and/or S770) the row in the chart refers to, again shown by an 'O' or an 'X'.
The next (4th) column is the one listing the System Setup parameters. Anything with an 'O' in this column along with an 'O' in the S-970 column will be reset when you carry out a System Setup reset. It includes things like Set Points, Chord Fingering Type, as well as many others, but it will not delete any user files on the User or USB drives.
If you have downloaded the 'Reference Manual', you will find further information about how to carry out various resets, and how to back up existing setups if you want to be safe, in the section 'Setup Files' on page 131, and 'Reset' on page 132.
Regards
Ian