I’ve done some more testing and realized I made a mistake – I forgot to restore the DTV 480p setting after initially setting it (I realize that’s what profiles are for, I just forgot after turning the OSSC on and off, new owner mistake). This led me to discover the reason I didn’t notice the problem on the first day I got the OSSC. The problem occurs only when 480p in Sampler is set to either Auto or VESA. The device heat seems to have no effect on signal stability in DTV mode, while changing the sampler setting instantly destabilized the signal after a long operating period. I ran the Dreamcast for 90 minutes @ 480p in DTV mode with no issues, flipping sampler back to VESA or Auto after operating for this long caused the LED to flash red and the LCD to show the strange 525p/525i/1050i output you can see in the pictures from my previous post.
Setting sampler back to DTV 480p returned the signal stability immediately.
@BuckoA51 I’m sorry I didn’t realize the above sooner, did you test the OSSC 1.6 in DTV mode?
I understand that DTV 480p mode is the recommended setting for the Dreamcast but I assume Auto/VESA still shouldn’t exhibit this kind of problem, right?