A2600 Heavy Possibly faulty?

Hi guys, I am hoping to get some help here as I recently bought a Heavy Sixer and had it shipped to Australia. It was console only, advertised as tested and working.

I do not seem to be able to tune it in and I am concerned I have a hardware fault. I haven't mentioned this to the seller as I am not sure it is a hardware fault and may be something simple I am missing.

I am tuning it in to a multi standard tv that accepts NTSC signals and does tune low enough to be able to tune the NTSC in. Full disclosure here and I am using a Sega Megadrive RF box with the physical Game/TV switch. I have previously tested this RF box with an intellivision and it was working fine.

The result I am getting when this is tuned in is a picture with static sound only, unable to pick up any game sounds. The picture is poor quality with static in the image.

I have attempted to adjust the pot that is under the hole in the RF sheild which alters the static on the screen, too far one way and diagnonal lines appear in the image, with the same result the other way, there is a sweetish spot that gives the best picture but no sound still.

So, at this point I am at a loss.

Any ideas?