Hi @Simon Marsh,
Don’t know the answer but here’s the [link|https://elektrotanya.com/sony_fdr-ax30_fdr-ax33_fdr-axp33_fdr-axp35.pdf/download.html|service manual] for the camcorder. Be patient as it takes a little while to go from processing to Download ''after'' you have passed the security check and clicked on Go to Download below the document preview box.
Check what error codes (if any) are stored in the camcorder and see if that helps to further isolate what the problem is. Go to p.17/130 (pdf page numbering) or ''Sect.1. Trouble Shooting'' to see where to find the codes in the menus and also what they mean.
Hopefully this is of some help.