I'm planning to build a consolized MVS with my MV-1FZ board as the centerpiece 8)
I'd like to pass the correct video signal levels on to the SCART, but I don't have an oscilloscope, and I haven't had much luck googling the information, so now I'm asking you guys:
What is the amplitude of the R, G, B and CSync signals from a MV-1FZ board?.. 5Vpp?
If i'm not mistaken, a TV with SCART expects video amplitudes of 0.7Vpp. But is that only regarding the R, G and B signals? I've got a feeling, that the CSync line needs special attention.
Also, what value of capacitors would you recommended for removing the DC offset?
I found that putting a 75 Ohm resistor in series on each of the RGB and CS lines produced a good picture on the TVs (tubes and LCDs) I tested my supergun with both my MV-1FZS and MV-2B boards. As for caps I didn't use any on my old supergun but I will on new one and I found out different TV's handle DC offset in different ways. My component to SCART adapter (made from a hacked up Wii VGA cable) I use to connect my Blu-Ray to my TV worked ok on my Panny but caused my current Toshiba to flicker badly. I added some 220uf caps (value picked purely at random) in series to the RGB lines (neg leg to output) and the picture improved immediately.
But I would wait and see if any of the other regulars have any better advice as I don't have any hard facts, only my own experience to go on.
Use 150 to 220 ohm resistors in series on the RGB lines to get the appropriate levels. The XRGB series (prior to the mini) has a 220 ohm setting that drops the voltage down to acceptible levels. I use 150 or 160 ohm resistors. IIRC with 75 ohm resistors the signal is still a bit too strong. Any RGB input should have 75 ohm resistors to ground. Adding a series resistor creates a voltage divider circuit. Hence, with a 75 ohm series resistor, the math works out to be 75 / (75 + 75) = 0.5. So the voltage is halved. 150 ohm would be 0.333 (one third), and 220 ohm would be 0.254.
I believe the MVS RGB output is DC coupled, and not AC coupled, so a cap isn't necessary. I'm sure it would be fine to experiment though. Perhaps user viletim can shed some light on this.
Quote from: RGB32E on January 26, 2012, 01:36:31 PM
Adding a series resistor creates a voltage divider circuit.
I know. If the amplitude was 5Vpp, I would need to use a 470 ohm resistor to get it down to ~0.7Vpp. But I guess the amplitude isn't that high on an MVS board. I think I'll just put some 500 ohm potentiometers on the R, G and B lines. That should have me covered :)
But what about the sync line? I've seen some SuperGun designs with a 1K resistor on that one. Does the SCART standard specify a very low amplitude on the sync line?
Quote from: RGB32E on January 26, 2012, 01:36:31 PM
I believe the MVS RGB output is DC coupled, and not AC coupled, so a cap isn't necessary.
Awesome! That's nice to know :)
Quote from: RGB32E on January 26, 2012, 01:36:31 PM
Perhaps user viletim can shed some light on this.
I'd might send him a mail. He seems to know his way around arcade/scart RGB :)