Mine is a slightly newer generation (Z9D), but I'd expect the function to be the same. I do remember seeing that some recent generations required a firmware update to activate the RS-232 "mini-port." I had a little trouble at first, but I did get it working.

In any event, I basically did the following:
* Got an RS-232 to 3.5mm converter from Amazon
* Confirmed that the pin-out was correct (tip=Rx, ring=Tx)
* Set the IP control parameters as specified (On, Normal & Pre-Shared Key)
* Set RS-232 control to "Via serial port"
* Set Standby to "Enable"
* Turn the set off

It may or may not be important, as I'm not entirely sure which of my tweaks finally got it working, but try sending Standby Enable as the FIRST serial command, before Power On.

Also, make sure the baud rate is at 9600. I had it too high at first, based on an older Sony protocol doc. Speaking of which, I still don't have a current RS-232 command list. After dealing with five levels of Sony support! It's ridiculous that they don't just post this on the product support page like every other manufacturer....