On certain Sony Professional BRAVIA TV models it is necessary to send a Standby Enable RS232 command before it is possible to control the TV. See the list of supported models in the attached document.
We have made the code here and added the checksum as well, but if you wish to study the material from where we derived the code, have a look here.
Standby Enable [HEX] = 8C 00 01 02 01 90
Have a look at the attached guide from Sony that describes i.e. that you need an interface box in case your model doesn't have a RS232 mini-jack input directly. There are also some settings needed to be done in order to enable control.