Sega mega driveII AV problem

[playman]

I have this SMDII and works fine, wanted to get a better picture from it so I made my own 9 din to
SCART cable, used a 9din cable that I found laying around, think it had a plug similar to what Samsung note 10 uses.
Pin 4 had no wires connected to it so I bridged 4 and 5 and shortened the 5 pin.
I get good picture and sound on the TV but the image is shaking alittle.
Any idea what could be the problem?

I used this schematic to make the cable.

[R_J]

Re: Sega mega driveII AV problem

How long is the cable? If it is of any real length I would use shielded cable for each of the colors and the audio.

[stj]

Re: Sega mega driveII AV problem

the 75ohm resistors are wrong,
get rid of them.

composite video is 75ohm, not rgb.
and you dont use them like that anyway - they go to ground.

you may want to put one in the sunc signal though.

[playman]

Re: Sega mega driveII AV problem

How long is the cable? If it is of any real length I would use shielded cable for each of the colors and the audio.

It's only 60cm long

the 75ohm resistors are wrong,
get rid of them.

composite video is 75ohm, not rgb.
and you dont use them like that anyway - they go to ground.

you may want to put one in the sunc signal though.

Is that schematic correct then?

[stj]

Re: Sega mega driveII AV problem

it's an improvement.

[playman]

Re: Sega mega driveII AV problem

I did those modifications, it still shakes as before.
I noticed that the SCART ports were differently marked, AV and then RGB.
When in RGB port it shakes, but when in AV port it's pretty steady.
I thought this was a RGB mod and therefore should work with the RGB port, right?

[R_J]

Re: Sega mega driveII AV problem

It's likely the sync signal is not compatable with the tv. or it is too low in amplitude or even wrong polarity. What do you mean when you say it shakes? does the picture shake from side to side or shakes up and down?

[stj]

Re: Sega mega driveII AV problem

https://pinouts.ru/Home/Scart_pinout.shtml

replace the 75ohm resistor with something higher,
and put the 75 ohm resistor between sync and ground at the scart end.

[playman]

Re: Sega mega driveII AV problem

It's likely the sync signal is not compatable with the tv. or it is too low in amplitude or even wrong polarity. What do you mean when you say it shakes? does the picture shake from side to side or shakes up and down?

I took a video of it, was unable to upload a video file so I had to zip it.
It doesn't show as well on camera though
maybe my wording of it wasn't the best.

https://pinouts.ru/Home/Scart_pinout.shtml

replace the 75ohm resistor with something higher,
and put the 75 ohm resistor between sync and ground at the scart end.

Sorry but not quite understanding you.
There is only one 75Ω resistor in that schematic, or are you talking about the 180Ω resistor that I should make higher? and how much higher?
Made another schematic of what I think you were talking about.

[stj]

Re: Sega mega driveII AV problem

that's close, but also put a resistor in series with the sync wire to lower the voltage.

[stj]

Re: Sega mega driveII AV problem

this is interesting:

using a cap to change the sync level

[R_J]

Re: Sega mega driveII AV problem

Its hard to tell by that video but it does'nt seem to be a sync issue. looks more like noise in the video signal.

[CapLeaker]

Re: Sega mega driveII AV problem

interesting, almost looks like a cheap unshielded scart cable is used.

[stj]

Re: Sega mega driveII AV problem

well we are stabbing in the dark here.
we know what a tv expects,
but we have no idea what voltages are coming out of the console.
testing should really be done with short wires too - for the reason you mentioned.

[playman]

Re: Sega mega driveII AV problem

The cable is exactly 95cm.
The cable is just a 9din to PDMI (I believe) that i found at a flea market, not much of a shielding on it, I think
its only the ground that is braided over the inner wires, the cable diameter is 4mm.
As you might have guessed i'm just a electronics hobbyist and did not finish much school in electronics,
but I do believe I have the basics and I've able to repair many electronics with and without help.

I guess i'll just order some 9din connectors from ebay and use a spare scart cable I have here with it, that should remove all
doubt regarding the cable and the shielding right?

[R_J]

Re: Sega mega driveII AV problem

That 95cm is long, when you are talking about video signals. Each of the R, G, B, should be using shielded cable, and I would also use a shielded cable for the sync and for the audio. Find an vga monitor cable, cut off the ends, and use it.

[CapLeaker]

Re: Sega mega driveII AV problem

get yourself a quality scart cable first. Backtrack a loong time ago, my scart cables were much thicker than 4mm. Those thin ones are cheap and also perform as such.