90s consoles video issue

[RetroPlays]

Hey all I modded my master system to have 50/60hz and composite video. It works great via composite however I want to use a av2hdmi so I can record gameplay.
Once I connect it to the console and to the tv via hdmi the picture goes to black and white. No idea why, it's not the av2hdmi box as it works with my original Xbox without any issue and my 360.
My megadrive also does the same as the master system, I'm assuming it's the consoles that are causing the issue.

Has anyone else had this issue? If so how did you fix it or anyone have any ideas, I'm happy to try anything.

Tldr: works fine through composite but is in black and white when using av2hdmi

[zapiy]

My initial thoughts are what version MS is it? Pal or NTSC?

[Vadergb]

Tldr: works fine through composite but is in black and white when using av2hdmi

NTSC will play in black and white if the TV can't output 60hz. Is the av2hdmi outputting at 50hz or 60hz HDMI? The TV should have a information button that shows what signal its receiving. Have you tried it on any other HDMI ports on different screens?

[RetroPlays]

Sorry for the late reply, it outputs at 60hz for the consoles and that must be the av2hdmi as the megadrive isn't 60hz modded.

Both consoles are pal (I'm from the uk). I've since tested with my n64 and it worked perfectly so must be the sega consoles.

Is there a way to fix the video issue.