Little problems with RGB cable

[LordC]

HI!!

This it's my first post on this site, so here we go...!!

I'm trying to make a universal scart cable (like GAME STAION X webmaster cable; I use 1 connection cable for all my systems and a small �terminal� connector on the system side) so i have questions and troubles:

1. I get a functionally RGB cable (with audio off course) from a SEGA 32X/CDX but it's lacks Red signal (I have uses 25v/100microF condenser, 10v/100microF condenser, direct connectio,10/220 microF) and i get no RED signal, the line continuity and connection it's tested and Ok...) some idea? (it's tested on 32x/cdx sistem)

2. For a general RGB scart cable (PSX, Dreamcast, Saturn, Genesis, Master System, 32x...) there are some kind of general value for the RGB condenser?

3. Due i want and RGB/YC(SuperVHS)/Composite scart, should i change the resistor on the 8-16 pin? maybe some kind of variable resistor or a small switch with different resistors? some idea?

From HwB:
Pin Name       Description                        
8    SWTCH  Audio/RGB switch / 16:9    
Signal Level     
0-2 V=TV, 5-8 V=WideScreen, 9.5-12 V=AV Mode

Pin Name       Description                        
16  BLNK       Blanking Signal        
Signal Level     
1-3 V=RGB, 0-0.4 V=Composite

...some idea?    

4. The sync signal on scart it used for? (On my self made RGB scart cable and a stock Saturn cable, the sync line it's a �empty space�, just only the 8->resistor->16 connection)

5. Some general improve ideas?

6. I have connected the ground video signal lines to a chassis due the old systems doesn't come with separate ground line? some suggestions about this? (on the scart side have separate ground signals)

7. Putting ferrite cylinders over the end's of the cable give real improve?

8. I have references that it's useful to use a 47 pF non polarize ceramic condenser to get decent YC scart signaling. It's true? i make some, non affordable, RGB/Composite quality/functionality loss?


ThX a lot's!!! and see ya!! (and sorry for my poor English and worst electronic skills)

y add a pdf scheme to help to understandme

[NFG]

and i get no RED signal

Then you've got a wire that's either broken somewhere or connected to the wrong spot.  

there are some kind of general value for the RGB condenser?

Unfortunately not.  Some cheap chinese cables use 100uf, most original cables use 200uf, but some - like the Saturn and the European SNES - require no caps at all.

I can't really help you with SCART questions, never been to a PAL country.

I have connected the ground video signal lines to a chassis

Ground is ground, it doesn't matter where it's attached as long as it IS attached.

Putting ferrite cylinders over the end's of the cable give real improve?

I've never noticed an improvement, but they'll never HURT the signal.  If you've got spare ferrite chunks you might as well use them.

I have references that it's useful to use a 47 pF non polarize ceramic condenser to get decent YC scart signaling. It's true?

I've never heard of this.  Try it and let us know.  =)

[Guest_LordC]

Hi Again!!!

Now i have made a "redesing" about this SCART problem, i was looking on internet and find a maxim ic that it's a multi op-amo and can be used to multiplex a wide range on video signals on scart pins (for example using a dc which output cvbs, yc and rgb at the same time..and due the scart uses the sames pins for r/c y/cvbs... well....inow i not very inspired...i will send a schema


sorry and thxs

[Guest]

My advice is to seperate the grounds for each r,g,b signal.Ground is ground but if you ever plan on using a large tv/projector or using long cable lengths seperating the grounds will help maintain quality.However it will only be useful if you use twisted pair or coaxial cables..seperate grounds on a straight through cable will do nothing.Keep your video and shield grounds seperate in any case as you can get noise from running these together.A ferrite bead(or cylinder) is always a good idea,but may not make a difference...it is proven that running the 5v line from an xbox through one will block out noise on a focus video chip xbox.Lastly and most importantly don't make adapters or the like as extra soldered connections is the biggest degrader of quality.Just one cable from the console to the tv/monitor...don't make an adapter that can convert between different monitors,tv's as you will likely get some interference even on small monitors.Preferably use coaxial or twisted pair cables too.....twisted pair is recommended because they are very cheap as you can just cut up a cat5 cable and use a seperate pair for each signal i.e red + ground,green + ground etc.Unfortunatly you can't fit anything more than rgb + sync on a cat5 cable so you may want to use a cable with more wires that connects to the console such as a vga cable and then make a breakout box straight after the connector...you can hook up the cat5 for the rest of the cable that hooks up to your scart cable.Alternatively you could install RCA connectors on the console itself for audio which shouldn't be hard to do at all.

As for your other questions:
1/2.Generally use a 220 uf capacitor as this is the standard but if you encounter problems on a particular console remove them.Usually if the signal is ac coupled inside the console then you won't need the caps.
3.A variable resistor may work but you are better off just wiring a switch to pin 16 as 0v will bring the pin low which enables composite mode.You will need switch to enable the svideo pins too as their is not enough room on the scart connector for both svideo and rgb.Check the scart svideo pinout for the correct pins to switch.
4.Sync is on the  composite video pin which is pin 20 IIRC.Most tv's will take either composite video or composite sync on this pin for sync.
The rest of the questions I anwswered at the top..I am not sure about question 8,do you have links for information about that?

[Aidan]

Running coax for the signal lines is not a bad idea. You get to seperate the video grounds from other grounds, which can made a difference in some circumstances.

If there are seperate returns for RGB on the device you're connecting to, then it's worth maintaining these seperate returns. If there are no seperate returns, star ground them at the output device end.

Pin 16 on the SCART connector is not sync, but blanking. This pin is used to inform the display device if the signal is RGB or Composite, so it can switch to the appropriate input. It would be wise to use a seperate pin on the 15pin D connector for this, as not all devices output RGB. This way, the cable between the console and the 15pin D would determine if the display device is expecting RGB or composite.

For devices that output RGB, you would use a 75ohm resistor to connect pin 16 on the SCART connector to 5V. This will result in approximately 2.5V appearing on pin 16 of the SCART connector.

For devices that output svideo or composite, you would connect pin 16 to ground. This will ensure that the display device is expecting a composite signal, not an RGB signal.

Pin 8 on the SCART connector is used to inform the display device that the device connected to the SCART socket is generating a valid output, and that the display device should switch channels to the AV input. If you have a 16:9 display, and you wish to device to use widescreen mode and switch to the AV input, then connect this to 5V. If you just wish to have the display device switch to the AV input when you power up your console, then connect this to 12V.

If you have a console or other device that requires capacitors on the RGB lines, put them at the console end of the cable. That way you don't degrade the signal for devices that do not require capacitors on the RGB lines. Typically the capacitors are only there to remove a DC signal from the RGB lines.

Strive to use the best available signal from a device. If you have a DC, then use the RGB connections, and don't worry about svideo or composite. That way you get the best picture quality from each device, and do not have to worry about multiplexing.

[Guest_LordC]

Thxs!!!!

1. Thxs for the suggest
2. Now i have studied more about scart and i belive that i understand it:
a. There are a rgb/composite switch pin (now i don't rebember) so originally you can easily change from RGB to CVBS. BUT WHEN THEY ADD SVHS SIGNALS they use the r and CVBS lines so...now you have 3 video inputs. rgb, cvbs and svhs and you have to modes RGB vs CVBS/SVHS so if i want a multifuntion cable (duei move my consoles from diferents places and tv) and must desing a cable that provides all signals (at least RGB/SVHS and CVBS) and use a maxim ic that multiplex/switch the Red/Chroma and CVBS/Luma so... i get 2 switchs: 1 to chage from RGB/CVBS(+SVHS) on the �16th pin? and one switch to control tjhe multiplexer (that switch between RGB+CVBS vs SHVS)

I will send and scheme and we will speak again...so fornow we ca say that this thread it's closes (WIP) ;P

thxs agains and sorry for my sucking and fuckin english

[Aidan]

If all your TVs can handle RGB, then you can get away with nothing more than some passive components. That's the big if though. If that's an acceptable restriction, then you don't need to worry about multiplexers and other such things.