Stedy's RGB to SCART cable

[Jope]

In that case you might succeed. :-)

[Stedy]

Hi Steven,

The Holo3DGraph should work with the Amiga. You may not need the 330 ohm resistor on the CSYNC output. Professional grade video equipment expects TTL level sync pulses, which the Amiga provides on the CSYNC, HSYNC and VSYNC outputs.

Let us know if it works.

Ian

[StevenMarshall]

I will post detailed infos if i get it working.

[Cloudane]

Sorry if this isn't the right place, I figured it's better to use an existing SCART related topic...

On either of my Amiga 500s (I have two at my disposal) if I use an RGB-SCART cable the signal is a little noisy on my TV (Panasonic Viera). It's most obvious during the "shades of grey" when the 'mig is powered up but is always there - there are a couple of horizontal... how to describe it.. "fuzz lines", kind of like interference. They don't impede the visibility of what's on the screen, but are distracting. The lines scroll slowly upwards.

I've tried:
- Different Amiga
- Different PSU
- Disconnecting other input sources
- Unplugging other powered items in the vicinity
- Removing Pin 19 from the SCART connector
- Putting aside the cable I was using and buying a high quality SCART cable from Amigakit

Anything I can do, or think it's just crappy inputs on the TV that I'm stuck with?



Edit: My mistake. I was disconnecting other input sources one at a time...
The more inputs that are plugged in, the more noisy the SCART picture. If I leave EVERYTHING unplugged except for the Amiga, it goes away (there's a little bit of vertical striping on grey colours which "P-NR" - noise reduction - 95% sorts out)

[Kitch]

I've just made an Amiga to SCART cable as per Stedy's diagram and I get a good picture on my 19" ViewSonic N1900w LCD TV but icons and window borders seem to have a slight shimmer/jiggle to them. I get the same result when trying an A600, A1200 & A1200T. I don't have any other LCD's with SCART to test if it's just an issue with my LCD TV or my cable. Any ideas what might be causing the shimmer and how I could remove it?

I couldn't find any shielded cable so I used 2m of .5mm 12 core robotics flex. The cable had eleven numbered cores and on green earth core, I connected the earth core to the outside of the SCART socket (pin 21) but I just cut it of at the Amiga end.

I didn't add it to my cable but I was wondering what is the optional composite video connector used for?

After trying all the well known electronics stores in town for Amiga 23pin DBF connectors I was beginning to think I would need to hack up a 25pin connector but I managed to get one off an electronics supplier that I use for work. He had been sent a whole lot of 23pin DBF sockets by mistake years ago instead of 25pin DBF's and he had no use for them.

[orange]

I believe optional composite is there if you want to use composite out from Amiga. SCART connector on TV can be used with RGB, composite, s-video, even YPbPr. It depends on TV which ones are supported on the particular connector. http://en.wikipedia.org/wiki/Scart

so if TV has only Composite in SCART, that option could be handy. (or as a test) in that case, you probably don't need to connect 23pin connector at all (but since some Amigas have only black&white composite and some none, you might need A520 modulator)

[Kitch]

Just out of interest I tried the LCD with SCART connected and a separate composite cable from the Amiga to the LCD, I could get a picture from both cables. The picture from the SCART cable was obviously the best and when I changed input from SCART to AV I got a colour composite picture but it was not very sharp, quite soft around the edges compared to the SCART image.

[Kitch]

I connected up an A1200 that I had fitted an Indivision AGA Mk II to and took some photo's (all cables were connect at the same time, I just selected the input via the remote).

1st photo is from Indi AGA Mk II, the 2nd is via SCART and the 3rd is via Composite.

The best image is the one from the Indi (DVI@640x480) despite the black strip down the left hand side, it's sharp and has no shimmer.

My SCART image is not as good as the Indi one, it has slight ghosting and a faint shimmer.

Lastly is the Composite image that is not as sharp as my SCART image and still has a slight shimmer as well.

I need to find another monitor with SCART to test if the shimmer is just related to my LCD.
If I can get rid of the shimmer the SCART image would be a great solution for me as far as hooking up Amiga's to a LCD goes because it's just a cable I can use with any Amiga and not a piece of hardware that needs to be fitted into it. Too many Amiga's and only one Indi.

[Stedy]

Hi,

I have been thinking about this and have two suggestions.

The shimmer could be related to the de-interlacing of the video by the TV electronics. Nothing you can do if that is the case.

The other option, something I missed, is the DC offset of the Amiga video signal. Black level is about 600mV, it should be 0-50mV. This has an easy fix, on each of the RGB signals, add a 220uF capacitor, + end to the Amiga output. This will AC couple the video, with minimal droop. Does this fix any of the issues?

Ian

[Kitch]

Hi Ian,

Thanks for the reply.
You could be right about the internal de-interlacing of my LCD TV, I've still been looking for a different TV with SCART to test my cable on but SCART's not that common on LCD's in NZ.
I'm quite happy to have a go at modifying my cable, any chance of providing a diagram of where the capacitors need to be connected?

[orange]

@Kitch
I think he means cut the (R,G,B) line and connect capacitor between two ends (+ to the Amiga end). AC signal 'skips' the capacitor, DC is blocked.
this just if you can't wait for his reply.

[Stedy]

Hi,

Just finished the diagram in Visio. As orange said, you need to cut the RGB lines and add some 220uF/10V capacitors. See the attached diagram.

Ian

[Kitch]

Thanks for the diagram, I'll give it a go and let you know how it works out.

[Mr B]

Originally Posted by Stedy

you need to cut the RGB lines and add some 220uF/10V capacitors.

Could this (possibly) fix the slight ghosting my Amigakit cable has on my mates TV?
Even if it's a long-shot, id be trying it, but if it's in "there's no way" territory, then i wont bother with it. There isn't a whole lot of space in the scart connector, and i'm sort of equipped with the temper. You know, the short fuse, high velocity powder keg kind of temper... (Ok, so it's not that bad, but i'd hate to ruin a perfectly good thing, if there isn't a shot at fixing the issue.)

[Kitch]

I've attached the caps as per the diagram but I can't see any real improvement with the image quality. I still have a slight shimmer/flicker and a little ghosting, the same as I had before.
In some ways it's a good thing it doesn't seem to have made an improvement because I had no idea how I was going to fit the caps inside the plug and attach the top cover.
I've attached a couple of pics.

[dJOS]

Originally Posted by Stedy

Hi,

Just finished the diagram in Visio. As orange said, you need to cut the RGB lines and add some 220uF/10V capacitors. See the attached diagram.

Ian

Thanks Ian, Im going to try this on my GBS-8220 and see if the PQ improves - I already have the 300ohm resistor on csync but it made no difference either way so I've left it in place.

[orange]

@Kitch
I remembered there might be another use for 'optional composite video connector'. on my panasonic plasma, screen is offcenter. I've read somewhere thats because TV doesn't expect 'raw' composite sync signal (amiga pin 10). so 'optional composite' should in that case provide better picture (tv will decode csync from amiga composite RCA).
(it takes some time to strip sync from composite, lack of that delay causes off center image.)

[dJOS]

Originally Posted by Stedy

Hi,

Just finished the diagram in Visio. As orange said, you need to cut the RGB lines and add some 220uF/10V capacitors. See the attached diagram.

Ian

So I tried out your latest design Ian and the result was quite good, a slight but noticeable improvement in PQ - Less vertical banding and a little less motion artefacts around the mouse when using my GBS-8220.

I even managed to fit it inside the Connector shell!

Not my best soldering work (I've re-used that connector a few time hence the mess) but you can't see it inside the shell so I dont care!

[orange]

@Kitch, dJOS

why don't you put capacitors in SCART socket, it has more room?
I also have ghosting problem. and some noise.
but most of noise goes away after connecting shielding.

[Kitch]

It still kind of tight inside my SCART connector, I've removed the caps from mine and the picture quality is about the same.
My cable is unshielded though, maybe that could be part of the problem.