Problem installing 19.10

[Colin Law]

I downloaded the Ubuntu 19.10 desktop image (sha sum checked) and
burnt to an SD card (16GB).  On booting into it I ran the Check Disk
option first, then Run Ubuntu and all seemed ok.  I selected Install
Ubuntu and at the What do you want to do dialog I selected Something
Else then selected the 40GB partition that I had already formatted as
ext4 (using gparted in a working Ubuntu 19.04 partition) and told it
to mount it as '/' and not to format, then told it to continue.
At this point it hangs with the wheel spinning.   I left it for an
hour but it was still spinning. I burnt the image to a different SD
card and tried again with the same result.  It also hangs if I select
the partition as '/' and tell it to format it.
Any suggestions as to what I can try?

Colin