Question about 220uf capacitors on RGB mode

In my Project Unity system, i'm running all systems I reasonably can on RGB (PS2, NeoGeo, Saturn, SNES, TurboGrafx, DreamCast, MegaDrive, SMS, GameCube, Jaguar, GX4000), and the rest on composite (NES, Atari 7800, Intellivision, N64, Colecovision). (that list includes the systems not already incorporated yet into the system BTW). All these systems connect, as separate systems, to a SCART (i'm UK).

I put a 220uf capacitor on each of the RGB and C-Sync/composite lines a while back, as i'd read that it was "good practice" as gave best stability on picture image and also easier on the modern television (is that true BTW?).

Up to the point of having the PS2, NeoGeo, Saturn and DreamCast working, all was fine. I then added the NES (composite) and it refused to work unless the capacitor from the C-Sync/composite line was removed, then it worked perfectly. Ok, tested the DreamCast and Saturn with that change, no issue. I've now installed the SNES (RGB) and the image starts fine for a fraction of a second then gets rapidly dark, refusing in other words to work with the capacitors on the RGB lines - remove them, and the SNES image is perfect and lovely being RGB. I've not tested on other systems installed to date so far, but considering I started out with not using the said capacitors a while back, and image was fine, I doubt the visual image quality will be any different as a result.

So, I have a question, and as i'm not electronics minded i'm asking those of you who know the answer to please advise! The question is: is there any reason not to remove those capacitors entirely (any benefit/reason to keep them, especially as the SNES doesn't seem to want them)? I can attach the capacitors to the systems separately if there is a reason to do so, but if not, then no point using them and may as well remove them.

 

I think the caps are there mainly for imager cleanup. If the console puts out good image without them I see no reason to leave them off. I don't think they serve any other purpose than that. Of course I don't use SCART or even RGB so I can't say from experience. You might try contacting one of the other members here who know more about SCART and RGB. BadAd84 is a good one to go ask about this.

 

True dat, the entire purpose of caps is to clean signals, because they do that. I think the purpose of resistors is to shrink signals since they make bright video dark, seems logical, but I dunno, I'm high on crack, and 12.

 

I detect severe crankiness on this post... XD


Bacteria: The purpose of the capacitors are stop DC current from flowing through the cable (you want only the signal to flow, not the electricity itself) and if the capacitors are missing, the current flow will muffle the signal. Adding two sets of capacitors are no good either.

The resistors are there for impedance matching.

A good example is the NEO GEO AES and the MEGA DRIVE. Both use the CXA1145 RGB encoder inside, that chip requires a capacitor and a 75 ohm resistor in series to the RGB amp output to match the impedance and stop the DC current from flowing. Yet SEGA choose to be cheap and decided that most people won't use RGB. So they saved a few pennies from putting these parts on the cable instead.

Due to that design choice you cannot use a original MEGA DRIVE RGB cable with a NEOGEO as you will have two sets of capacitors + resistors in series with the RGB cricuit resulting in a horribly weak signal.

 

Here I thought capacitors were there to raise costs to keep the proletariat out of the RGB market.

 

I was wondering about this too. I bought some 220uF Panasonic 6.3v caps to put in my mini PS SCART cable though. Same rating as in the official SFC and DC cable. Looks pretty good to me.

 

That's right, the PAL Gamecube and NTSC SNES/ SFC also require the capacitors in place on the SCART end. That's why you get such a dark image when you use a Gamecube RGB SCART on a PAL SNES, as the PAL version does not require the caps.

 

In all seriousness, whether you need capacitors depends on 1) the amplifier driving the cable, and 2) the circuit receiving the signal.

My answer is do what the original console does, they do it for a reason.

Output capacitors are somewhat a thing of the past, they were necessary to block DC when amplifiers had a significant DC offset, and they were important for short-circuit protection. Now a lot of equipment omits them because 1) output capacitors DEGRADE the low frequency components of the signal which is why you need such large ones 2) they aren't perfect at removing a DC offset and if a signal isn't DC-balanced which video signals are not, a virtual DC offset will actually be introduced and cause the signal to slowly wander 3) lots of amplifiers are more robust now.