The schematic diagram shown by leosadvs is wired to the sense pin code for a fixed resolution of 1024 x 768 @ 75 Hz. As the LC does not support this sense pin code, it falls back to 512 x 384 @ 60 Hz (as diagnosed by porter). To fix the adapter, cut the connection from pin 4 to pin 7 (DB 15, Mac's side) and tie the same pin 4 to ground. This will provide the sense pin code for a fixed resolution of 640 x 480 @ 67 Hz.