RGB -> Scart - Help

Hello Amiga fans!

I recently got the urge to play some old games on my brothers' old Amiga 500. After connecting the RF adapter to the TV though I was presented with a flickering black & white picture with no sound. I tried to use the screws on top of the RF adapter to tune it but it didn't do much for the picture, I also tried to switch between Hi and Lo on the front but again this didn't do much.

So after finding a page on how to create an RGB to Scart solution I decided that maybe this would help me experience the old games from the past. Me and my father made a DB23 female connector from a DB25 female connector, solded the wires and finally completed the whole product. When we tried it though the picture was just white, but at least the sound played correctly when a game was loaded into the Amiga.

After stumbling upon this site I read about another fellow who had also made an RGB to Scart solution. What I was confused about was that he had apparently used more wires and pins than the site that I got mine from.
(The one I followed http://www.jeacle.ie/pub/articles/scart/ - The other one http://eab.abime.net/attachment.php?...1&d=1212934877)

I wonder now, has the site that I have followed forgotten some pins and is the other one correct to follow?

Any respons and help is greatly appreciated and do forgive me if I ask a frequently asked question. Also my knowledge in the electonic department is fairly limited so do use big words when explaining.

Many thanks in advance
Darkkanex

[prowler]

Hi Darkkanex, and welcome to EAB!

Amiga to SCART is a much discussed subject here, with no simple, one-size-fits-all solution.

The best advice I can give you is to browse these related threads:
http://eab.abime.net/showthread.php?t=40183
http://eab.abime.net/showthread.php?t=41327
http://eab.abime.net/showthread.php?t=41380
http://eab.abime.net/showthread.php?t=41572
http://eab.abime.net/showthread.php?t=44985

You will find that some are cross-indexed and there are also external links given to schematics and troubleshooting guides.

Good luck, and please let us know how you get on.

prowler

[Rabbit80]

If you can, try your cable on a CRT TV.. LCD's are strange and difficult at times I have just completed a A520-S-Video mod because I can't get SCART going

Thank you! I will look to the threads at once and try to figure something out, and for the record the TV I'm doing this on is a CRT, so no problems with an LCD here =)

Hmm...A quick question, currently I have no resistors connected to the R G B channels (neither the Composite Sync), would perhaps this be the cause of the white screen? If I then applied some resistors to the R G B channels so the resistance is 75 ohm on each (like it says on one of the schematics) could this work as a solution to my problem?
Sorry if this idea defies all laws of physics, was just an idea that struck me while I was browsing through these enormous amounts of RGB -> Scart threads

[Rabbit80]

From what I can gather, the 75 ohm resistance "should" be provided by your TV. It is much more likely that the problem is to do with the RGB switch if you are doing it on a CRT TV - so you might need to check voltage on that line.

Originally Posted by alexh

Check the voltage between ground and pin 16 (RGB select) and pin 14 (GND).



Pin 14 should be gnd and pin 16 should be +1v to +3v.



If pin 14 is unconnected or floating you'll need to tie it to ground with a small section of wire.

If pin 16 is unconnected or floating you'll need to wire it to the Amiga's +5v (via an appropriate resistor to bias the voltage).



Make sure LCD supports RGB via SCART.

[alexh]

75 ohm is the input impedance of the TV.

Sounds like you have the same problem as Rabbit, you have a TV which blends RGB with Composite video and the voltage coming from the Amiga on the CVBS pin is too high. (i.e. CSYNC)

If you have an A4000 you can enable SOG (Sync on Green) via a jumper and remove the wire on the CVBS pin and if your TV supports SOG then you are sorted.

If you have an A1200/A600 you could try providing CVBS signal from the CVBS (yellow) RCA output instead of CSYNC on 23-pin D. However there is no guarantee that this will work as there may be a delay through the video encoder.

[patrik]

Originally Posted by alexh

Sounds like you have the same problem as Rabbit, you have a TV which blends RGB with Composite video and the voltage coming from the Amiga on the CVBS pin is too high. (i.e. CSYNC)

My god! Can't come up with any scenario where you would want your tv to blend the RGB and Composite video. Why on earth do they do that?

[alexh]

I had never heard of it, seems crazy to me but the information came from Ian Steadman so I trust it.

Originally Posted by alexh

75 ohm is the input impedance of the TV.

Sounds like you have the same problem as Rabbit, you have a TV which blends RGB with Composite video and the voltage coming from the Amiga on the CVBS pin is too high. (i.e. CSYNC)

If you have an A4000 you can enable SOG (Sync on Green) via a jumper and remove the wire on the CVBS pin and if your TV supports SOG then you are sorted.

If you have an A1200/A600 you could try providing CVBS signal from the CVBS (yellow) RCA output instead of CSYNC on 23-pin D. However there is no guarantee that this will work as there may be a delay through the video encoder.

I see..weird with the TV, it's quite new (a Phillips widescreen TV from around 1999) so one would assume that such a function would be disabled. Anyway, I have an Amiga 500 so I'm afraid that I cannot use any of your advice, thanks for trying though .

I tried to test my RGB -> scart cable on another CRT TV (this one is also a Phillips but an older 4:3 version) with the result of a black screen instead. I might add that the sound works perfectly, which makes the picture problem even more annoying.

One last thing I might add before I resort to digging through those threads again (which I think will result in me giving up, I'm already beginning to think that this problem is far greater than my knowledge in tech), before doing the RGB -> scart cable my father and I tried the theory by solding wires from scart pins directly underneath the RF modulator's DB23 solding points. This resulted in a quite clear black & white picture being shown on the TV. Don't know if this piece of information can help in solving this problem though.

[Photon]

Video ground problem or just two TVs that don't have RGB Scart but only composite-video Scart? That's my guess, anyway.

To test if your TV supports RGB scart, connect a games console such as PS2 with a scart cable and if the colors are "bleeding" then it uses composite and not rgb. Or what the hell, I dunno, get the TV's specs and check if it support RGB via scart (such as my reading the manual, if you still have it.)

[alexh]

I thought you had an LCDTV. This changes things. I've never known any RGB capable CRT not work, even with no ground.

Chances are you've made a mistake in your wiring. Double check SCART pin 16 is wired correctly. Without this pin wired correctly you will get no picture.

[Zetr0]

@Photon / Darkanex

I have been having hell and all trouble getting SCART RGB on my plasma!

have a read here it may help.

http://eab.abime.net/showthread.php?...ght=scart+woes

Originally Posted by alexh

I thought you had an LCDTV. This changes things. I've never known any RGB capable CRT not work, even with no ground.

Chances are you've made a mistake in your wiring. Double check SCART pin 16 is wired correctly. Without this pin wired correctly you will get no picture.

Then perhaps I have some chance at getting this to work!

Hmm..the schematic I have been following (http://www.jeacle.ie/pub/articles/scart/) doesn't have the SCART pin 16 wired to anything, so neither do I..could perhaps this be the problem? Or did you mean pin 16 on the DB23?

And if the Scart pin 16 is to be wired..then what should it be wired to and do I have to bear something in mind whilst doing this?

Oh and Zetr0, (sorry for double posting) I did read through your thread earlier and it provided some useful insight..the thing is though that I have a CRT TV with (I'm now almost sure cause when changing to the channel it says EXT 1 RGB) RGB scart(s) and still get the same problem as you did with one of your attempts (white screen of d00m) on a plasma TV..which is weird, shouldn't it work with a CRT compatible TV that has/have RGB scart(s)? *going slightly mad*

[quantum112]

Just to chime in here, sorry for hijacking your thread but I've something of an issue with SCART cables as well, mine works properly and image is displayed normally, but the colors are really weak and as if they lack vibrancy/saturation, not sure how to explain it. Also, when the floppy drive is accessing a disk, I can see the screen warping and shaking near the edges, every time the disk does a tick. Any idea what I should check?

[alexh]

Originally Posted by Darkkanex

Hmm..the schematic I have been following (http://www.jeacle.ie/pub/articles/scart/) doesn't have the SCART pin 16 wired to anything, so neither do I..

This is a very poor Amiga SCART wiring diagram! It does mention Pin16 at the bottom.

Originally Posted by Darkkanex

could perhaps this be the problem?

Almost 100% certain.

Originally Posted by Darkkanex

And if the Scart pin 16 is to be wired..then what should it be wired to and do I have to bear something in mind whilst doing this?

SCART pin 16 is RGB enable. Without this pin being driven (1v-3v) the TV is expecting a composite video input. The Amiga 23-pin connector does not output composite video and so you would just get a blank screen.

SCART Pin 16 needs to be wired to Amiga Pin 22 (+12v) via a 1KOhm resistor to lower the voltage to 1-3v.

You probably want to wire in several (all?) grounds. At least one, SCART pin 18.

If your soldering skills are upto it you should wire all grounds together.

SCART pinout
Amiga video pinout

[alexh]

 SCART		   Function		     Amiga	    Notes
-------+-------------------------------+---------------+-------------------
Pin 1	|				|		|
Pin 2 	|	Audio input		| RCA		| (right)
Pin 3 	|				|		|
Pin 4 	|	Audio GND		| RCA		|
Pin 5 	|	Analog Blue GND		| Pin 18	| (SCART pin 7 ground)
Pin 6 	|	Audio input		| RCA		| (left/mono)
Pin 7 	|	Analog Blue		| Pin 5		|
Pin 8 	|	Aspect Ratio		| Pin 22*	| Via 1K ohm R (9.5-12V)
Pin 9 	|	Analog Green GND	| Pin 17	| (SCART pin 11 ground)
Pin 10	|				|		|
Pin 11	|	Analog Green		| Pin 4		|
Pin 12 	|				|		|
Pin 13	|	Analog Red GND 		| Pin 16	| (SCART pin 15 ground)
Pin 14	|	GND			| Pin 20	| (SCART pin 12 & 16 GND)
Pin 15	|	Analog Red		| Pin 3		|
Pin 16	|	RGB-selection		| Pin 23*	| Via 220 ohm R (1-3V)
Pin 17 	|				|		|
Pin 18	|	CVBS input GND		| Pin 19	| (SCART pin 20 ground)
Pin 19 	|				|		|
Pin 20	|	CVBS input		| Pin 10**	| (TTL voltage)
Pin 21	|	GND			| Pin 20	| (SCART pin 8 & 10 GND)
-------+-------------------------------+---------------+-------------------

*Take care to measure the voltage on these two pins to make sure they are in range. Use the right value of resistor to lower the voltage from +5v to 1-3v.

All the ground (GND) pins on the SCART connector should be wired to an Amiga GND. You do not need to use individual wires to separate pins (as indicated in the table above) because all the GND's on the Amiga side are wired together on the motherboard. Just wire any Amiga GND to any SCART GND and then wire up the remaining SCART GND's together using short bridge wires in the SCART shroud.

**SCART Pin 20 (wired to Amiga Pin 10) is out of voltage for SCART specification. I think it is a TTL voltage level signal (5v) and SCART expects a 1v input. Most CRT TV's are ok with this but if you have tried everything else you could try to lower the voltage on this input using an in-series 270 ohm resistor.

NOTE: Information extracted from two web-pages listed previously. I've doubled checked for errors, but you should double check yourself, perhaps use a second source.

Originally Posted by alexh

[code]
All the grounds (GND) on the SCART connector should be wired. While you could fully wire up all grounds as in the table above, practically you will not have enough wires in your cable. Just wire Amiga PIN 20 to one SCART GND and then wire them all together using short bridge wires in the SCART shroud.

**SCART Pin 20 (wired to Amiga Pin 10) is out of voltage for SCART specification. I think it is a TTL voltage level signal (5v) and SCART expects a 1v input. Most CRT TV's are ok with this but if you have tried everything else you could try to lower the voltage on this input using an in-series 270 ohm resistor.

NOTE: Information extracted from two web-pages listed previously. I've doubled checked for errors, but you should double check yourself, perhaps use a second source.

My father and I changed the Scart Pin 17 to 21 (the shield) and the Amiga pin 16 to 20 (those two were a pair), solded new wires to Scart 8,Amiga 22 & Scart 16, Amiga 23. We also added a 217,5 ohm resistor in series with the Scart 16, Amiga 23 cable. However we didn't do anything more since my father didn't see the point in adding bridges from all the cables on the Scart to the ground on Scart 21 (the shield). So we plugged it into the TV and...worked like a charm! Great picture, sound and all...finally I can play the games from my childhood!

Many thanks (all of you!), your help was much appreciated! (Smiley abuse)

[patrik]

Originally Posted by quantum112

Just to chime in here, sorry for hijacking your thread but I've something of an issue with SCART cables as well, mine works properly and image is displayed normally, but the colors are really weak and as if they lack vibrancy/saturation, not sure how to explain it. Also, when the floppy drive is accessing a disk, I can see the screen warping and shaking near the edges, every time the disk does a tick. Any idea what I should check?

Make sure there are no resistors in series with the Red, Green and Blue signals - this will give a picture with low maximum intensity - ie low contrast. Such resistors can be found in either the dsub or the scart connector - please consult pinouts in this thread for which pins to check for resistors on.

This is a common mistake, so I suspect there are some wrong instructions for building amiga scart cables floating around. This error is also very common on cables you buy from amiga stores unfortunately .

Also make sure your grounds are good - video and audio ground wired together into one wire for example is not a good solution. Atleast separate video and audio grounds. Preferrably all signals should have a separate ground, check the schema alexh posted for proper instructions how to wire the grounds.