This started happening a few weeks ago. Skimming as much as possible, it's hard to discern if it's a bad PSU (the multimeter indicates it's fine), if caps need replacing, or something else entirely. I'm convinced, with no evidence, that the A/V port is bad, but can't prove it.
Any thoughts? I've tried all cables on another Saturn, so whatever the issue is here is definitely in the console itself.
What kind of cable? The TV says it is getting a HDMI signal, so you are likely using an upscaler, which means that your upscaler, cable, and console can all be suspect. PAL and NTSC consoles have differently wired A/V output, and that can cause issues if you are using a cable that isn't universal.
Thanks for checking in - it's a Hyperkin HDMI cable. Both it and two RF cables I have work fine with A/V output on the other consoles I have (one US, one JPN). I have the utmost confidence it's the console in this case. Below is the same console with an RF cable instead of the HDMI.
(Edit: it may not be entirely clear from this video, but with the RF cable, there's loads of audio noise as well, but the audio/video don't cut out)
I'm not familiar with that cable but at a guess I'm going to say that whichever pin it taps to extract c-sync has too much noise, possibly because the EMI filters in the console are dead for that specific pin, and the converter in the cable box cannot handle this. It could also be the filtering caps aging (which results in the same issue), or perhaps contact issues for that specific pin.