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  • Joined: 14 Mar 2013
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  • Location: Belgium
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Making my own RGB cable
Post Posted: Sun Sep 23, 2018 8:38 pm
So I've been looking at making my own 1.5 or 2m RGB cable with DIN8 and SCART connector, using following images:
http://www.smspower.org/uploads/Development/rgbschem.png
http://www.mastersystem.dk/modding/rgb/ms1_md1_rgb_2.png
http://members.optusnet.com.au/eviltim/gamescart/megamstr.png

From the cables I've seen online, I couldn't see anyone using a coax cable and I'm wondering why?
RG179 75Ohm impedance cable is perfect for this and isn't too expensive.

When doing a component mod, on the super famicom for example, you'd use RCA cables, which are coax cables (for the high quality ones).

I also want to know where would be the ideal place to solder the 75Ohm and coupling capacitor. I've seen some place it in the SMS on a perfboard, but other placed it in the SCART connector.

How did you make your cable? Pictures are welcome.

Any advice is always appreciated.

PS: Sorry if this isn't the correct forum to post this.
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  • Joined: 31 Oct 2007
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  • Location: Estonia, Rapla city
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Post Posted: Mon Sep 24, 2018 11:09 am
Coax is expensive which is why nobody is using it. All the cheap cables on ebay are non coax and usually not even shielded so there will be massive buzzing in sound etc.
I have made my RGB cables out of VGA cables, works really well as long as it isn't a cheap cable using copper plated steel wires...

The resistors and capacitors should be at the connector.

http://www.tmeeco.eu/BitShit/SCARTcable.jpg
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  • Joined: 14 Mar 2013
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Post Posted: Mon Sep 24, 2018 3:08 pm
Hey TmEE, thanks for the picture. I can't see the caps though, where did you put them ?
I haven't measured anything yet so I don't know what the RGB waveform looks like, but I'm guessing it's a DC signal. Isn't it easier to AC couple this before putting that signal through a long wire ?

I've found my coax on reichelt, it's 8€ foor 5m. Good enough for a 1.5m DIY cable.
Also, I chose RG179 for it's small diameter (and price).
I don't think it's that expensive, if you compare it with other coax cables.
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  • Joined: 31 Oct 2007
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  • Location: Estonia, Rapla city
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Post Posted: Mon Sep 24, 2018 6:08 pm
I don't actually have the capacitors there. It will put bigger strain on the output drivers of the RGB encoder due to 150ohm load in idle condition but it isn't a problem. Almost all TVs have series caps on their RGB inputs also so the DC offset is not a problem either and there will not be any brightness gradients possible or sync issues from level drooping that happens if the series cap is too low in value. Plus there's no aging components.
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  • Joined: 14 Mar 2013
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Post Posted: Tue Sep 25, 2018 2:29 am
Good to know! I do have the 220uF caps shown in the images above so I might try with and without just to see if there's a notable difference.
If I don't forget I'll post a few pictures when I'm done.
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Post Posted: Wed Sep 26, 2018 10:29 pm
While I'm at it, are there any worthwhile mods I can/should do ? I own a SMS2, can't remember which motherboard version (if there are more than one).
I don't own NTSC games so I don't know if a 50/60Hz mod is useful.
I do have a master everdrive.

Maybe an audio related mod ?


Also, the 220uF seems to be for NTSC, not for PAL. Just found that out today.
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  • Joined: 14 Mar 2013
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Post Posted: Fri Sep 28, 2018 10:18 am
I managed to make the cable but man was it hard to do with the coax.
I do not recommend it.

The coax is very thin and there's little to no support for the cable on either side, so one of those will probably brake loose if you're a tad too rough with the RGB cable.


On the other hand the image on my flatscreen TV is amazing.


TmEE: I've put my resistors inside the SMSII, right on the RGB pins. I just didn't feel like the connection between the resistor and coax would last long.


Quick video comparing RGB and RF : https://twitter.com/pyroesp/status/1045620505493946368


A bit more info about my cable if someone wants to know:
5 coax + 2 wires:
- Coax are R, G, B, CSync, Audio (mono).
- Wires are +5VDC and GND.
Added a braided cable sleeve to make it look better and not have loose cables.
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