The CM-5 HW seems to be OK. 5V supply voltage is correct, uP clock is running etc.
If I try to write anything from Robot Termnal on a PC via the cable, the CM-5 responds after exactly
2 written characters (any of them) with six lines of same error response i.e. in this way:
> ## (without CR, same effect with two CRs)
When trying to download a hex firmware file with Robot Terminal, same printouts seen on the screen during the download.
When powered on or reset with the mode button,
CM-5 writes one octet of data all bits set i.e.
hex FF to the serial line.
Have you seen this kind of behavior before?
My guess is that the firmware is corrupted due cosmic radiation during transit or something equally weird. Another possibility is ESD shock.
Is a special JTAG tool or at least different file format needed to be able to send the firmware in binary format into CM-5 not having runnable firmware already.