Super Famicom official JP21 cable (SHVC-010) reconfiguring?

[Ergot]

Is it possible to reconfigure this cable (by swapping pins) to work as a EURO SCART cable for NTSC SNES and SFC consoles? I've read that the JP21 connection was only found on monitors, so was it made with 75 ohm termination in mind for standard TVs or was it intended for use only on monitors in Japan?
I have changed an official PAL SNES cable from composite video as sync to use luma as sync by opening up the console connector end and swapping the pin over, so I wondered if it would be as simple on the JP21 cable?
Obviously I know that I will also have to swap over pins at the SCART connector end too.

 

[Trimesh]

Most of the signals are compatible - you might have to add a resistor for the fast switching pin because RGB-21 doesn't have that. From what I remember, that cable already has the 220uF caps in the RGB lines, so you should be OK there.

 

[Ergot]

I'm not really bothered about the fast switching as the NTSC consoles don't have 12v on the AV out for correct 4:3 output.

 

[Trimesh]

I'm not really bothered about the fast switching as the NTSC consoles don't have 12v on the AV out for correct 4:3 output.

That's the function/aspect ratio select on pin 8 - fast switching is the signal on pin 16, and you really should connect it up, since on some TVs it's the only way to enable RGB mode. It should be between 1-3V for RGB mode, and has a 75R termination resistance - so if you have a 5V supply and want to bias the pin to 2V, then use something like a 120R resistor. There is a resistor on the SFC RGB-21 cable PCB, but it's been so long since I looked at one of them that I forget what it does.

 

[Ergot]

I thought pin 16 was fast blanking and pin 8 was switching?

 

[Trimesh]

I thought pin 16 was fast blanking and pin 8 was switching?

Pin 8 was originally AV mode select (0 = TV, 12V = AV mode). Later the original AV mode was redefined as selecting 4:3 aspect ratio and 5-9V was used to indicate 16:9 aspect ratio.
Pin 16 selects between normal video (either TV or AV) when low and RGB mode when high. It was originally intended to enable the overlay of videotext decoders (or minitel) over the video, so it had to be fast enough that it could switch on and off in a character cell.

On old TVs, this was the only way to select RGB mode, but some of the later ones actually added a specific RGB input mode that didn't require the switching voltage. If you want a cable that is assured to display RGB on any TV, then you should connect both pins 16 (to 12V to select 4:3 mode) and pin 16 (to 1-3V to select RGB mode). Having said that, if you have a specific "RGB" menu item, you can likely leave them disconnected.

 

[Pikkon]

Would be way easier to just get a jp21 to scart adapter.

Also I would check the 220 caps in there,they can leak all over the board.

 

[Ergot]

I've done it! It works! Although the resistor between pin 8 and 16 was only 75ohm, so I swapped it for a 180ohm. My only concern is that there is no 470ohm resistor on the c-sync line, it might not be "CORRECT" but it works.

 

[Trimesh]

I've done it! It works! Although the resistor between pin 8 and 16 was only 75ohm, so I swapped it for a 180ohm. My only concern is that there is no 470ohm resistor on the c-sync line, it might not be "CORRECT" but it works.

The series resistor on the fast blanking pin is not critical - the spec says it should be between 1 and 3 V to enable RGB and it's got a 75R termination, so if you are running from a 5V supply anything between 50R (which gives you 3V) and 300R (which gives you 1V) will work.

The series resistor on the sync pin is also non-critical and really only there to accommodate some TVs that have input clamps and no internal series resistor.

 

[Pikkon]

I've done it! It works! Although the resistor between pin 8 and 16 was only 75ohm, so I swapped it for a 180ohm. My only concern is that there is no 470ohm resistor on the c-sync line, it might not be "CORRECT" but it works.

Just got my sfc rgb cable and I'm trying to doing the same.

Those's pins are a pain to remove,only got two out but sheer luck,you got any tips Ergot on how to remove them,I know there's a tab you have to move to the center,that's my biggest problem.

 

[Ergot]

I used a small screwdriver. Just slide it down the gap at the side of the pins and then gently push to the side while pulling up on the wire connecting to the pin. Most of them will come out very easily but some are more stubborn.

 

[Pikkon]

Thanks for your help,I managed to get them off.

What I did was use a paper clip,filed the end down like a flat-head screwdriver,then I bent the end just a bit and that worked really well.
I need to order some new caps as they leaked pretty good but other that the cable works great.