+AD4- Does it contain RS232 level shifters, or are
+AD4- the signals on the socket at TTL levels?
I do have a O'Scope handy, but a rather useseless
brain as regards to applying said O'Scope. An instruction
or two would help. Am I looking for 5v vs 15v signals?
The first thing I would do is to trace where the connections from the
serial port go. One of them, almost certainly the sleeve, will go to
ground. If the other 2 go to level shifter ICs (MAX272, 1488/1489, etc)
then it's RS232. If they go directly to the pins of a microcontroller or a
TTL chip, then it's TTL levels. If it's something else, come back here
with what you've found.
Also, measure the DC voltage (voltmeter, DMM) between the 2 signal
connections anf ground. If one of them is at a -ve voltage, then it's
almost certainly RS232.