A little progress update.
A replacement 8085 appeared in the post today, so I slotted it in - result..... Well, the green CPU led is now working, and the clock is running, and producing a T9 note as well
There is another oscillator on the card behind that wasnt wiggling at all, this was traced to a dead 74S04 - I only has 74LS04 in stock, so tried one of those instead - the oscillator is now also running.
Still nowt but rubbish on the screen though, so I guess next stop will be logic probe and see what the address lines are doing.
Thanks for all the helpful comments so far though.
Sean