I'm having a problem with my Ikegami TM14-20R monitor.
I've been trying to connect my Japanese N64 through S-Video, and this monitor accepts a Y/C signal through BNC connectors on the rear called "CH C" pictured here:

I bought one of those S-Video to dual BNC breakout cables to do the job: http://www.ebay.com.au/itm/131287846302 ... EBIDX%3AIT
And I got a couple of male to male BNC plugs so I could actually plug it into the monitor.
I assumed the breakout cable separated chroma and luma and that the monitor took them separately through the two inputs provided. However, when I set CH C's signal to Y/C in the monitor's menu, and switch the N64 on, I get no picture. If I revert the signal setting to the default "CH C" (I assume this makes it a third composite input or something), I get a black and white slightly warped picture with both cables plugged in, and a normal black and white picture if I have just one of them plugged in.
Also notable is that if I turn off external sync while CH C is set to Y/C, I get a flickering screen as if it needs a separate sync channel, but with no apparent picture coming from the N64 still.
Anyone know what might be happening?