I have some experience on Microtek 2800. It is so amazing that you still keep it working.
I saw your message the other day when I was searching for some answers.
I was very busy and not registered yet, so I could not give you any help then. Is that problem already solved or not?
It makes me feel guilty not respond to your problem. So I make registration and answer to you right away.
For a RS-232 communication problem, it can be categorized in 3 section.
1. RS-232 cable.
2. Settings of cnc control for RS-232
3. Settings of the PC software for RS-232
Without manuals I can only give you at least some idea for now. I am out of town right now. Please allow me send you more detail answer until I get back. I think I still have the manual for 2800, hopefully!
Don't worry ,I will get back to you.