Strange Sega CD + cable TV behaviour.

[Hamburglar]

I have a model 2 Sega CD with a model 2 Genesis.

Unit works fine on my Sony 19" CRT, XRGB2 to an LCD, however on a 36" Toshiba CRT it behaves strangely, it refuses to load some CDs, audio becomes scratchy, etc. be it games or audio.

As soon as I unplug the video cables from the set, and plug it in to the other sets, it plays fine. I tried plugging the power supplys to different wall sockets, used different power supplys, same problem.

I tried the unit on another CRT, a Sony 32 or so, same problem, so I narrowed it down to the cable line, the 2 problem sets are hooked up to a cable line/cable box.

As soon as I unplug the cable line from the cable box, or unplug the cable box itself the problems go away.

Now why would this happen? Is there something wrong with the Sega CD combo that makes it go nuts as soon as it's hooked up to a set with a cable line hooked up?

Could it be the laser diode is "weak" so whatever variations are going on throw it off?

I measure some voltage on the cable line, but they are throwing so much crap down it, I don't know what would be normal.

[Midori]

You are connecting the Mega CD to the TV via an RF lead? What happens if you connect it with composite leads instead?

[Hamburglar]

I forgot to mention, composite video.
Same problem if I take the audio/video from the official composite video cable, or the audio only from the RCA audio out on the CD unit.

[Midori]

Hmm, now that comlicates things... Not sure if it is relevant at all but you could perhaps try to measure the ground signal on the cable? It should be 0v. Is it still 0v when connected to the TV? Otherwise I'm having trouble seeing what the problem is. The only connections that is made to the TV is the ground, video and audio. All these share the same ground which makes me wonder at least. Although something is strange if the ground signal doesn't measure 0v when the machine is connected to the TV at the same time as the cable box...

[l_oliveira]

Do you have all shielding installed correctly ? It could be a current flowing from the SEGA system power supply through the television cable (which should be grounded).

If the shielding (the metalic part you're supposed to attack to the vents on the bottom of the SEGA Genesis/Mega Drive unit is not attached, all the grounding leak current will flow only through the data connector, which could be the cause of your trouble.

Have also you tried reversing the outlet pins (live/neutral) on both SEGA power supplies ?

[Hamburglar]

Do you have all shielding installed correctly ? It could be a current flowing from the SEGA system power supply through the television cable (which should be grounded).

If the shielding (the metalic part you're supposed to attack to the vents on the bottom of the SEGA Genesis/Mega Drive unit is not attached, all the grounding leak current will flow only through the data connector, which could be the cause of your trouble.

Have also you tried reversing the outlet pins (live/neutral) on both SEGA power supplies ?

Hello, yes, I have the metal shield between the Sega CD and Genesis 2.
I also tried reversing polarity on the ac adapters (hot/neutral), same problem.
Also tried 2 different Genesis 2 units.

[Hamburglar]

Hmm, now that comlicates things... Not sure if it is relevant at all but you could perhaps try to measure the ground signal on the cable? It should be 0v. Is it still 0v when connected to the TV? Otherwise I'm having trouble seeing what the problem is. The only connections that is made to the TV is the ground, video and audio. All these share the same ground which makes me wonder at least. Although something is strange if the ground signal doesn't measure 0v when the machine is connected to the TV at the same time as the cable box...

I tried measuring, nothing stands out, 7vac on ground off the composite video in jacks on the set. Same on the cable box connectors.
Difference between grounds on the cable line and the TV are 60vac though, seems kinds high no?  

[l_oliveira]

Do you have the small metallic plate placed under the big one (the one which hooks the two units together) ?
The small one touches the internal shielding on the Genesis and connects  it to the ground. On the SEGA-CD unit the top of it's internal shielding will
also connect to the big metal plate, completing the shielding circuit.

The extended shielding won't work if you're missing the small plate, using a MEGA Drive console (no internal shielding) or if you're using a black metallic plate from a MEGA-CD unit.

Asian/Japanese units don't come with the extra shielding as there were no equivalent to FCC regulations back then. In 1989 Japan issued a program called "VCCI"
(Voluntary Control Council for Interference by Information Technology Equipment) which then added regulations manufacturers were suggested to follow.

Nintendo did, so the Super Famicom complies and bears the VCCI logo.

Oh and 60 volts is high enough to fry your game console. If you have a Dreamcast, DON'T hook it to that set unless you AWAYS hook the video cable first, hook the controllers and all other peripherals and only when ready to power it on connect it to the wall outlet.

NEVER, BUT NEVER connect a video game video out cable to a TV set while the cable is already connected to the game system. Aways connect the cable to the TV set first and then to the game system. Also aways use legitimate 1st party cables as 3rd party ones may miss the outside shielding on the console side of the connection. That shielding is what keep the console from blowing when there is such weird voltages flowing around.

Dreamcast (as an example, but I've seen PS3s with blown A/V port too) consoles with the video out blown are more common than you think they are ...

[Hamburglar]

I have verified the internal shielding on the Sega CD and Sega Genesis unit are making physical contact.
Both are US/NTSC units.

I also tried a Turbo Duo, same problem. With both sets hooked up to cable.

The odds both units are not functioning correctly and both showing the same symptoms are really low I would say.

I am tempted to call the cable company to get them to check the line make sure everything is OK, however they usually are not very helpful.

Any thoughts?

[l_oliveira]

Not really, just make sure they fix that voltage leak.

If they fail to comply call the FCC. (Assuming you're in the USA)