Sega Mega Drive 1 Composite Issue

I own an NTSC Mega Drive Model I (it's a brazilian TecToy, so the plastic says Mega Drive II), the main issue I have with this unit is that whenever I run the console over composite the picture is in black and white and super blurred. However, through RF it looks fine (a little bit of ghosting sometimes, but ok).

I've tried it in several TV's, with two AV cables, and with a cable soldered onto the board (a standard composite mod), with no luck.

Any suggestion?

Thanks!

 

TecToy Mega Drive is a hybrid of sorts. NTSC-US game region mode, but different color encoding.
PAL-M should have a stable black and white picture on NTSC TVs. They're intended for the same resolution (480i) and refresh rate (60hz)

I don't know if it's been attempted, but attaching any NTSC 32X (American, Japanese, etc) in theory makes TecToy systems NTSC compatible. Since 32X turns the RGB to its own composite.

Anyhow, RF working when composite doesn't is strange. That I can't help much with.
Start by checking around the A/V din for a loose connection.

 

@Lum
Thanks! I don't think that's a color/region issue from what I know, actually these TecToy Megadrives came factory-modded with a 50hz/60hz switch. But this doesn't do any changes to the composite problem.
That was one of the first things I checked, but I found that these brazilian Megadrives have no problems outputting composite.

I've looked around the pins of the AV port and all seems pretty tight. I'm no any electronics savvy, but I could resolder those pins in case there's any cold-joint.

I found some schematics online, and from what I can see, composite video out and rf video both connects to the same pin on the encoder, so there's got to be something between the encoder and the composite out that's failing. Or it could be the ground pin as well.. just guessing.

 

A 50hz/60hz switch on its own won't work properly. PAL-M at 50hz is not a TV standard.