TTL C-Sync Megadrive 1?

[Chris230291]

Hello. Trying to use TTL sync as c-sync on my Megadrive 1.
I connected the TTL pin to the comp video pin with a 470 ohm resister in series.
OSSC detects the sync but I loose video.
If connect the sync back to comp video the picture returns, along with the serious jailbars I am trying to get rid of.

To clear up a few things... I removed the RF modulator and soldered on a Megadrive 2 din. Then get the signals from the original din solder points.

Any ideas why this doesn't work?

[Ryoandr]

you also need a capacitor (10µF, but common 220µf will also work)

[Chris230291]

you also need a capacitor (10µF, but common 220µf will also work)

Thanks for the reply.
I decided to redo my work on the top side of the board, getting the signals direct from the video chip. Pins 10, 21, 22, 23.
I added a 220uf capacitor before the 470ohm resistor.
All working now but still some jailbars.
I lifted pin 6 on the same chip but that didn't really seem to do anything.





On CRT these were invisible.
Any ideas?

[Fudoh]

On the mainboard the clock signal is running to close to the blue video channel. You have to lift pin 50 of the VDP.

[Chris230291]

On the mainboard the clock signal is running to close to the blue video channel. You have to lift pin 50 of the VDP.

Thanks for the reply.
I lifted pin 50 on what I believe is the VDP (the only square chip on the board with 128 pins) but still jailbars.
I couldn't measure continuity between pin 6 on the sony video chip and pin 50... I assume because it goes through other things first?
The model is IC BD M5 PAL VA4

[Fudoh]

this should be as good as it gets. Even the bypass boards for advanced RGB mods don't do anything different. They take the RGB signals off the VDP without allowing the signals to get degraded by being passed alongside clock signals on the board and on their way to the Sony encoder chip.

I've done this on half a dozen MDs, all with almost perfect results (though always NTSC systems or Asian ones modded back to NTSC).

[Chris230291]

this should be as good as it gets. Even the bypass boards for advanced RGB mods don't do anything different. They take the RGB signals off the VDP without allowing the signals to get degraded by being passed alongside clock signals on the board and on their way to the Sony encoder chip.

I've done this on half a dozen MDs, all with almost perfect results (though always NTSC systems or Asian ones modded back to NTSC).

OK thanks.
Just to be clear it is a huge improvement. Just not perfect.

[Ryoandr]

On some revisions, RGB signals also get poluted by nearby memory signals.

[AndehX]

Yeah lifting pin 50 of the VDP isn't 100% guaranteed to fix the jailbars. I have a PAL asian MD1 modded back to NTSC, and I even went as far as to remove the actual subcarrier trace from the board, and I still get jailbars. Voultar tried actually removing the VDP chip from the board, and wiring it up away from everything else and found that got rid of the jailbars 100%, so the jailbar issue is purely down to the location of the VDP on the board, and not just that subcarrier signal.