No sync in console mode upon vt-switch
A couple of days ago I replaced my Geforce 5200 based AGP card with a 6200 based one in my FC6 system. I made no other alterations, but now when I boot, although X does start & run fine with the nvidia driver, if I vt-switch (<Ctrl+Alt+Fn>) back to a console mode my monitor (Iiyama Vision Master Pro 454) reports no sync.
I *can* log in and do stuff, I just can't see it. I can also switch back to X on vt7 OK. I'll attach the bug report log as requested; it shows I use a vga= and a video= in my kernel boot, but I've tried without these, and also with a 'vga=normal' which was suggested in this forum 2-3 years ago, but to no avail.
Oh yes, and although I'm set up for running Beryl, I don't run it by default, so it's not that.
Any ideas what to try next?