Mega Drive interference on Sony PVM / BVM monitor

[MtothaJ]

Despite some intensive testing / troubleshooting I am still having a problem with what looks like interference, when connecting a Mega Drive to a Sony BVM monitor, which I hope you may be able to help me out with:

- with the Mega Drive, every so often I get some horizontal interference type lines appearing across the screen. The problem seems most apparant / frequent on a bright / white screen e.g. the ice rink in EA Hockey but will also appear from time to time in other games.

My setup is as follows: Mega Drive (VA4 High Definition Graphics model) connected via RGB Scart cable to a Sony BVM 14M4DE monitor via a BNC to female Scart RGB breakout cable from Retrogaming. Troubleshooting conclusions below:
- the breakout cable is fine - I also connect a Super Gun / Neo Geo MVS setup to the monitor with absolutely no problems
- monitor is fine also (Neo Geo MVS works great, so does e.g. a DVD player connected via Scart)
- cannot see any problems with the Mega Drive - I have connected it via Scart RGB to other TV's (a Samsung LCD and an older CRT) and there was no interference on either display), which rules out the cable. PSU is outputting correct voltage. Moreover I have since got another MD High Definition Graphics model machine and this is showing exactly the same symptoms as the first one. THe interference shows up regardless of whether 50hz or 60hz mode is seleted on the first machine as well as on the stock 50hz machine

I am slowly running out of troubleshooting options here - all the individual components appear to be ok, and in different configurations (different systems, TV's) work without any problems. Perhaps there are some option on the BVM that need to be chossen / enabled (?).

Any assistance would be most appreciated.

[evildragon]

Got the caps and resistors on the RGB and CSync lines?

My PVM requires it from the Genesis..

[MtothaJ]

Got the caps and resistors on the RGB and CSync lines?

My PVM requires it from the Genesis..

This is what the inside of my Mega Drive Scart plug looks like:

P1010760.JPG

[evildragon]

I sadly can't see what's in the RGB lines. Looks like resistors, but what about caps?

[MtothaJ]

I sadly can't see what's in the RGB lines. Looks like resistors, but what about caps?

It looks like I just got resistors on the RGB lines and nothing on the sync line.
Just bought some 75 ohm resistors and 220uf caps, need confirmation of wiring order, is it:
Cable from Genesis --> cap --> resistor --> pin inside scart plug?
How about the polarity of the cap - does the resistor go to the 'plus' or 'minus' terminal of the cap?

[evildragon]

Minus is towards the monitor..

Basically I'd put the 75 ohms resistors before the caps..

So Genesis, resistor, cap, monitor..

[MtothaJ]

Minus is towards the monitor..

Basically I'd put the 75 ohms resistors before the caps..

So Genesis, resistor, cap, monitor..

Thanks - just finished soldering 3 resistor + cap combos. Doing one more and then going to work wire them up to the scart plug. Will post update.

[evildragon]

Sweet, can't wait to hear your results.

With my PVM without all this, it had difficulty even syncing, so it should help a lot.

[ApolloBoy]

Your RGB lines aren't grounded, connect all the ground pins of your SCART plug together and that should help with the interference.

[MtothaJ]

Evildragon, AppoloBoy - many thanks for your valuable advice, rep to you

Below is my modified scart plug - cap / resistor combo added to RGB and sync lines; ground lines connected:

P1010768.JPGP1010769.JPG

Despite the additional gear, I managed to fit it in the standard scart plug cover. BVM fired up in RGB, picture looks crisp - at least I didn't dick anythign up
As for the result - don't want to declare victory prematurly since need to spend some time testing but so far these appear to be v. promising since haven't seen any interference yet
WIll keep you updated.

PS. In case anybody is wondering the stock cable just had resistors on the RGB line, nothing on the sync line, ground points unconnected

[evildragon]

Awesome, glad it's looking good so far. I'm not familiar with SCART so that was a good catch RGB wasn't grounded either.

[MaxWar]

Doesnt the MD1 already have caps inside the console on the RGB lines?

Also, You got that cable from RetroGaming cable in UK right?
They use composite instead of CSYNC in their cable. IT results in jailbar on my PVM. The cable had to be modified to use CSYNC on the console plug side.
Which happens to be a pain to take appart...

[evildragon]

Don't think the MD1 does. I have a VA3, and without the capacitors, I had some issues getting the picture just right. I thought it does too. I'll need to probe it next time it's open.

It definitely needs the resistors though, which it seemed to already have.

I thought when he said stock, it was a SEGA branded cable.. Yea, if it's using Composite video for sync, use C sync.. It'll also help clear it up too.

[MaxWar]

I have the same cable I bought from the same place as op. It definitely has the resistors inside the shrink wrap.
I had to modify my cable to use Csync and added caps but it was the model 2 cable.

I just looked back at the email conversation I had with that guy at Retrogaming Cables ( I was sort of blaming them of wiring their RGB scart cables wrong ). I was responded they did it this way to ensure compatibility with Scart TVs that did not have RGB but used composite instead.

He then said He did not put the caps in the cables because the console already had them but then that was a genesis 2 cable. But then I had checked and he was wrong. So he went and checked too and was like OOPS. I hope they put caps in their model 2 cables since.
I have not checked for Genesis 1 but seeing how they made the mistake for my model 2 cable, they might as well be mistaken too for their model 1 cables.
Theirs cables are well soldered and assembled though, very clean job on the inside.

[evildragon]

It's definitely clean, and I appreciate seeing heat shrink tubing too, you don't see many people actually trying to be that clean anymore.

Here's my VA3.



Sadly there's no clear view of the traces to see where those caps are connected too. Maybe there is, but I know on my system, I needed the caps still in the cable.