Thanks Sirius,
Yes, this is a problem i have also considered - I am looking to see if I can find someone with another machine that is functional - if I can, I will take a copy of a functional eprom, just in case.
If the datasheet of the 8085 is indicative of this application, then the firmware will almost certainly be on that eprom.
The processor is too hot to touch after 5 minutes of operation, so I think this is a fairly reliable indication of an issue.
Yes, it is a shame that I have already ordered a selection of replacement 8085s, I should have enquired here first I guess.
Back to work today, so playing time is limited again
Thanks
Sean