If it is a 25-way D connector - and wired for RS232 - then only pins 2, 3 and 7 would be needed (ignoring the hardware handshake signals for now). Trace those 3 pins back and where do they go on P102?
If you measure the voltage between pins 2 and 7 and between pins 3 and 7 on the 25-way D with a multimeter set to DC volts (reading 25V or so full scale) what do you read? The RS232 transmit line should have a healthy voltage reading...
Dave
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