TGZ framebuffer in a SparcSTATION 1+

Hi,

I recently dug my SparcStation 1+ out of storage and 
in no time its up and running and now upgraded to 
64M memory - I never realised I could do that :)

Anyway I've currently got a cg3 style colour framebuffer
fitted which works fine, but thought I'd try my TurboGX
framebuffer (501-2325).

However with the TGX fitted, the Sparcstation doesnt 
boot at all.

I'm guessing this is some kind of PROM/ROM issue - so
the question is - what kind of grahics card upgrade 
could I use here?

Thanks

Ian