I got a TV with a cracked screen that otherwise works fine, which I managed to change the inputs to "AV" (3 RCA jacks). So I amputated the screen and now have a mini stereo with remote. The only problem is that I can only hear the L & R line inputs when a video signal is fed into the (yellow) composite video jack. Right now, I use a video camera to provide the necessary signal, but I'm looking for other (cheaper) ways to trick the circuit into producing sound. I'm hoping for easy. Wild guess: use a 555 to produce blips at some frequency, amplitude, and duty cycle?
You can use Arduino to determine which synchronization signals are required.
It may be that only vertical (V-sync) or only horizontal (H-sync) synchronization impulses are needed.
You can later build the desired signal on the 555 timers.