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How to use SCART for our hobby
Eversynth:
Sorry for not providing more informations earlier. I have conducted various tests, and I'm still going mad.
I am using PCI (not PCIe) ATI Radeon 9250 with 128MB RAM.
My VGA-SCART cable is wired in the simplest manner:
VGA 13&14 twisted together to get composite, connected to scart pin 20.
A bridge between scart pin 20 & pin 16 to give it the rgb signal. If pin 16 is not connected the TV can't display the image even when setting it to EURO AV.
The R G and B colors connected to the proper pins on SCART.
All grounds (R G B, vga pin 10 and VGA chassis ground) twisted together and connected to scart pin 5 (blue ground).
I have tried various grounding combinations (the ground colors where separated before), nothing changes. The scart pin 16 gets 2,4v, so it's within standards 4,5v, turns out the measurements done on the scart end of the vga cable were different than those who arrived at the TV.
The color doesn't work with only the Scart Wii Cable. It needs to be shorted to the Wii.
NOTE: in the wii only scart pins 17, 15, 11 and 7 need to be connected for this to work. I disconnected all the other pins, they have no effect.
The same thing applies when using a gamecube and its rgb cable instead of the wii.
The TV is generic, a no-brand. I don't know the manufacturer.
NB: The TV is not so old as I make it sound. I purchased it in 2006. It has menu options even for color modes (Pal, secam, two different ntsc, auto), but they don't solve the problem.
UPDATE:
Sacre Bleu!
If I put a 1N4148 diode between Scart Pin20 and scart Pin17 (that is now empty), the colors show fine!
UPDATE 2:
So, I noticed that, with the Wii connected, the voltage on pins 15 11 and 7 was around -4,5v (using pin 17 as ground).
Since I have +4,5v on pin 20, I used that.
The diode is added like this: Pin20 ->|- Pin17.
Now I can't keep the Wii scart connected, or the image gets darker (dim), and with a little distortion between high contrast elements (brights objects on black background).
Any idea on what's going on is appreciated...
(The Wii has been used a lot of times. The PC has seen a lot less use as of later.)
Zebidee:
It occurs to me that your VGA-SCART cable has no ground at pin 17! This is probably the most important grounding pin.
But when the Wii cable is plugged in, the Wii provides a ground for pin 17 (even when turned off). I suspect that the pin 17s on both of your TV's SCART inputs are common.
You should try hooking ground up to pin 17 on your VGA-SCART cable. Have you tested for continuity between your gnd at SCART pin 5 and pin 17? You might find that they are not common & therefore that there is no ground for your sync signal. Bridge these pins with a short wire.
Eversynth:
--- Quote ---This is probably the most important grounding pin.
--- End quote ---
Good to know, so that's why in Wii & gamecube cable that's the only ground wired.
But I have to tell that before wiring up the VGA-SCART the way I have now, it was different:
I had:
--- Code: ---VGA 13 & 14 - Scart 20
VGA 10 - Scart 17
VGA R G B to Proper Scart R G B
VGA R G B grounds to Proper Scart R G B grounds
Scart 16 bridge with Scart 20
VGA shield ground to Scart shield ground
--- End code ---
In fact, the second VGA-Scart cable is still wired like this. And it works fine only in the second, "Good TV".
The VGA pin 10 ground in Scart 17 ground doesn't affect at all the outcome.
--- Quote ---Bridge these pins with a short wire.
--- End quote ---
In the new cable I already tried shorting Scart Pin 5 (all grounds) with Scart Pin 17, to no avail.
The only solution seems to be using the 5v coming from the vga 13&14 and put it on scart 17 with the diode, to get the needed(?) negative voltage on the scart R G B pins. :/
Zebidee:
You've got me - I can't see why you have the problem, nor truly understand why the diode helps. Which way around was it?
You could try the 5v -> 100ohm resistor -> 2v -> SCART pin 16 (and gnd to pin 18) trick. This might give you a more consistent RGB switching signal.
I'll normally use this kind of cable, also with 12v at pin 8, as a 'baseline' cable for SCART TVs. I have one lying around somewhere in casew I need it. I have never yet seen a RGB SCART TV that not accept this input and give a clear picture.
Eversynth:
--- Quote --- nor truly understand why the diode helps. Which way around was it?
--- End quote ---
The diode ground on pin 17, the other on pin 20.
It helps in giving current to the colors signal, albeit a negative one. The reason why it works only with pin 20 could have something to do with the sync signal coming from it.
I don't know what's going on.
The only logical explanation is that the TV needs some voltage in the RGB pins.
Without my trick the Vga outputs only between +0,01v and +0,02v there.
Maybe something broke in the tv, even if it seems unlikely.
All of this started because I wanted to add the 12v on pin 8 and 2v on pin 16, and then (maybe for the first time with the Wii disconnected) I noticed the colors problem. :)
It wasn't even really noticeable without looking at a color gradients pattern.
I don't know if something in the tv might have broken when I connected the 12v coming from the PC molex to the scart (it was a little higher, between 12v and 12,5v).
For sure it worked, switching automatically to the correct AV channel.
I'll think later about adding those again.
In the meantime I will have to keep the PC and TV on for an unprecised amount of time, to see if something breaks.... :timebomb: :D
I'll let you know if everything keeps working after testing.