As the title states, can the RGB lines on the monitor port of the Atari ST be used with the RGB inputs on a Sony PVM CRT monitor?
Yes. The STE monitor output uses a 13 pin DIN plug/socket. This is looking at the front of the plug:
1 2 3 4 5 6 7 8 9 10 11 12 13
7 is red channel, 6 is the green, and 10 is blue, these go to the corresponding RGB inputs on the PVM. 2 is composite sync and this should be connected to the external sync of the PVM. All grounds go to pin 13.
I created a cable using this configuration and no extra resistors/capacitors and great picture — just be sure to enable the external sync using the button on the front of the PVM!