Scart Cable Interference

Due to the layout of my room, most of the consoles are actually located to either side of my desk and monitor setup. This isn't a major issue for later stuff that uses VGA, DVI or HDMI, but some of the older consoles using Scart are showing quite a bit of ghosting in their output image.

This is how it is usually laid out:

Now, this interference shouldn't really be happening, as the older systems are all:

  • Using RGB Scart cabling
  • Being fed into a high quality Scart switch which has proven to work excellently
  • Being sent to the monitor through an OSSC, in most cases at the best output resolution (1920×1200 - aka line5x mode)

The problem is that the issue seems to be mainly be those systems to the left of my desk:

Not those to the right:

There are 3 possible routes that video can take to get to the screen:

  • HDMI → HDMI KVM → Monitor
  • VGA → VGA KVM → OSSC → HDMI KVM → Monitor
  • Console scart cable → scart extension → Gscartsw → OSSC → HDMI KVM → Monitor

Almost all of the consoles use RGB Scart, but I only see ghosting/blurring issues with some of them. The main ones that need solving (because the fuzziness is so distracting) are:

  • SEGA Saturn
  • Sony HB-FX1DJ MSX2+

Not all of my Scart cables are fully shielded, and even if they were, this is what they have to deal with:

The majority of the consoles Scart cables terminate somewhere around that left hand side under the desk. The rest of the distance to the OSSC and Gscartsw switch is extended by a dozen or so male to female Scart extension cables which then run in the cable basket until they get to around the mid-point of the desk and then exit up to the scart switch pretty near to the right-most side of the image.

Now those extensions are decent thickness, but clearly this isn't enough to stop interference brought on from the proximity to the rest of the cabling in this under-desk cable basket.

In hindsight it's obvious that running the AV cabling right next to the majority of the power switches and 240v mains cabling will introduce some interference. The question is what to do about it now.

To try and determine if it was the console scart cable at fault, the routing of the cable, the switch or the OSSC I bypassed the under-desk cable run and (where it was possible) ran the console scart cable direct to the scart switch.

In the images below I refer to the temporary test cable route as the shorter route. The other route being the under-desk cabling which runs in the cable baskets as previously shown.

Each image has the short cable run on the left, and the extended cable on the right.

Pseudo Saturn Kai menu (313p progressive), the ghosting is clear to see on the right image:

Panzer Dragoon Zwei menu screen (625i interlaced), zoomed out, both look pretty good:

Panzer Dragoon Zwei menu screen (625i interlaced), you can see the slight halo around the outside of the letters compared to the clearer image on the left:

Here's a few more good examples of the interference:

On the Saturn, interlaced modes hide the blurring/ghosting quite well, but that's down to the fact that the two fields are being overlaid on top of each other, cancelling out some of the ghosting of the previous field. My monitor (Dell U2410) does a decent job of deinterlacing the signal, so the OSSC is set to pass-through for 625i mode. In the above images all scanlines and post-processing is disabled.

Using the same scart cable as before, but changing to connecting it directly to the scart switch had a dramatic effect on the quality of the image - the new run is clearly pixel perfect and shows no sign of a ghost image or blurring. This obviously means that it isn't the console, scart cable, scart switch or OSSC at fault, but could be either the under desk route it takes or the longer extension it uses when connected that way.

Now if I can only find some way of determining what exactly is interfering with the signal when it runs in the cable basket…..

The first, and easiest test was to unclip the scart cables from the cable baskets and run it direct to the monitor, so that it didn't run over any power strips or power supply units

Cables unclipped and running on floor, up to monitor; almost no contact with active power supplies (sorry about the mess, that's the result of unclipping 12 scart cables!):

Alas, that made no difference what so ever to the image quality:

That says to me that it's not actually the route that the cable is taking, at least, any extra interference received from the power supplies is not making much difference to the already poor image that the OSSC is getting.

Next step is to try replacing one of the extended scart cables with another brand/quality.

So I ordered a high quality, fully screened Scart cable from Amazon:

It's certainly high quality; extremely thick outer cable, solid metal end covers, gold plated connectors and shielded individual wires.

With the high quality extension cable, it's not appreciably any better:

Need to try something else with the Saturn.

With the MSX, the picture quality is noticeably better, though some ghosting remains.

From left to right:

  • Original MSX cable and original extension cable
  • Original MSX cable and high quality extension cable
  • Original MSX cable and high quality extension cable + OSS filtering and gain changes
  • Original MSX cable and high quality extension cable + OSS filtering and gain changes + 12% scanlines

Although the interference remains, with some modifications to the OSSC filtering settings and some use of scanlines, the MSX output is just about bearable (actually, let's not be silly: compared to RF or composite, it's really good, just not perfect). The actual settings used are:

  • Scanlines:
    • On
    • S1 Strength: 12%
    • S1 Hybrid Strength: 93%
    • S1 Method: Multiplication
  • Video in proc:
    • Pre-ADC Gain: 5
    • R Gain: 20
    • G Gain: 20
    • B Gain: 20
    • Video LPF: 9MHz (SDTV)
  • Sync Opt.:
    • Analog Sync LPF: 2.5MHz
  • Output Options:
    • 240p/288p proc: Line5X

With these results, I'm fairly happy with what the MSX is now producing.

Since changing the extension cable that the Saturn connects to made no appreciable difference, the only thing left to do with that system now (other than move it to be far closer to the monitor - which, without re-arranging all of the other nearby systems, isn't an option) is to try an upgraded Saturn scart cable.

Well the cable arrived, and it certainly made a difference - all of the images below are with that cable and the original long scart extension:

The Rhea menu looked good, so I tried loading a game:

The image clarity is now equally as good with the scart cable and extension as it was with just the original scart cable connected directly to the gscartsw, so that's really good news.


White Balance Issues

However, this new cable has introduced a new problem; the white balance. More specifically the white balance sometimes shifts from bright white to slightly pink tinged. If you blink you can miss it, but it's cleared to see when you have an all-white image next to the same screen that is pink-tinged:

I really hope that it's just a loose connection somewhere along the chain, because to now have a pixel perfect image only to have everything tinged with pink every few seconds is just the icing on the cake!!!

[Update: July 2020] Yep, turns out that the new cable is a much tighter fit into the Saturn video-out port than the original, and it just wasn't pushed all the way in. Picture is now perfect, well, as much as an analogue RGB signal can be.

  • blog/blog_retro_scart3.txt
  • Last modified: 2020/07/26 08:51
  • by john