I have a Dreamcast that doesn't seem to output audio or video. When I power it on, the VMU beeps and the disc spins up, but I get no video or audio on the TV. I am using a third-party composite A/V cable that I have tested with another machine and verified to be working. (Specifically it is a 2014 Tomee AV Cable).
It is a Model 1 NTSC-U HKT-3020. The letters in the lower-left are 'AE', though I'm not sure what they mean.
Dreamcast A/V Issue
Re: Dreamcast A/V Issue
Maybe the AV pins are dirty on the DC that doesn't work. You could try cleaning them.