Hi, Neil,,
when i do this ,, i connect the mpeg board RF input to the DSP RF out on the CDROM PCB ..
so you can also look for this pin labeled in the PCB component side or if you didnot fing it then all you have to do that,, look for the DSP used in this CDROM ,,
like Toshiba , hitachi or some one else,,
if you find so,then you have to find the actual RF out pin by connecting a 0.1 uf capicitor to the RF input pin of your MPEG board and get it powered ,(also run any vcd movie CD in it), and by touching it on all the pins of DSP on the CDROM pcb one by one until you find the right pin.
when you find this ,you can look the image on the monitor or display of the running VCD movie in the CDROM drive.
wish you best luck..