In this article I will take you through repairing the OEM Nintendo Super Famicom RGB JP21 cable and then I’ll make my own JP21 to EURO SCART adapter so I can use this cable in my setup.
SHVC-010
This is the official OEM RGB cable for the Super Famicom in Japan. It was produced in limited quantities which gives us some indication about how popular the JP21 standard was in Japan back in the day.
While JP21 carried RGBs (as EURO SCART did), the Japanese had their own special plug for component video. When a system supported component, it was regular to see the typical 3 x RCA plugs, however what was even more common was a plug they called “D-Terminal”. This “Japan only” plug carried a component signal, just over a different connector. I made a video explaining this format if you want more information. If you have a “D-Terminal cable”, there are 3 x RCA breakout adapters to use it with regular component gear.
The standard for RGBs in Japan was JP21 and it’s electrically and physically identical to EURO SCART, the only difference is the pins are in a different order. In the second part of this article I’ll wire up a JP21 to EURO SCART adapter which is basically just a SCART extension cable which I have moved the pins about.
I found this OEM JP21 cable on one of my trips to Japan. It came without the box and was only ~20 bucks. That is a steal given eBay sales seem to start at 100 bucks and go upward from there. If you just wanted to play your Super Famicom in crispy RGBs in 2024, I suggest a more straight forward route and buy a quality, modern aftermarket cable from the likes of Retro Gaming Cables or a similar professional.
The SHVC-010 is a well built shielded cable with individually shielded wires. It uses the composite video (CVBS) line for sync. NTSC Super Famicoms have a dedicated CSYNC pin on the multi-out and this is not used. This has a few consequences:
- No resistors are needed on the sync line because CVBS is already attenuated.
- It won’t work with AV switches that need CSYNC, like an Extron Crosspoint.
- It won’t kill your PAL Super Nintendo system. Nintendo being Nintendo have a slightly different multi-out pinout between NTSC & PAL. Pin 9 on NTSC is CSYNC, while on PAL its 12v.
- If that CSYNC line was tapped and you plugged it into a PAL system, the cable would send 12v straight to you TV. That wouldn’t be good. Modern cable solutions like Retro Gaming Cables get around this by tapping composite video and then stripping out CSYNC.
- It’s still not a good cable to use on a PAL SNES because PAL needs different components in the SCART head, but it won’t kill your console or TV.
If we look at the NTSC to SCART wiring diagram, we can see that this cable is supposed to have a 220uf capacitor on each color line and a 180ohm resistor going to AV blanking.
Nintendo worked with the technology available in 1990 and built these components into a small PCB in the JP21 plug. 34 years later, the capacitors have definitly dried up. My first move was to replace them. It’s a pretty easy, through hole solder job which a beginner could handle. The solder will be very dry so use lots of flux and be patient.
Just for fun, I decided to check the resistor mounted into this PCB. While every wiring diagram I have ever seen for the Super Famicom lists a 180ohm resistor, I measured this one at 75ohm.
I am no electrical engineer, so I asked my friend Martin Hejnfelt and he explained that 75ohm works as well.
Resistors don’t generally need to be replaced over time so I left the original in place. The PCB looks a bit rough because of the years of corrosion and I didn’t want to mess with it anymore than I had to.
Button up the JP21 plug and that’s the SHVC-010 restored
Creating a JP21 to EURO SCART Adapter
As I live in the United States of Europe, every single thrift store has good quality SCART cables available. Most are usually male to male but I found this short male to female which will do the job nicely.
My plan was to switch the wiring of the pins around. At first I tried pulling the pins from the male end but this proved impractical. I ended up using my soldering iron to undo the joins in the female plug and move them around.
This diagram below shows the pin mapping between JP21 and SCART. The female end will have JP21 coming in and the male end will have SCART coming out.
I quickly got confused and forgot what wires were what. I had to break out the multi-meter and check continuity between the wires and the other end of the SCART. This was a slow process but not technically super hard.
I am not the most precise at soldering and the old solder joints often needed to be cleaned and re-tinned. Some of the wires were too short to connect to their new pins so I had to add in some extra wires to extend them.
After a few hours of soldering, checking, rechecking and testing, everything came up Milhouse. I plugged in the SHVC-010 and this new JP21 to SCART adapter and it all worked.
I tried this in my PAL GameCube and modded NTSC N64 and the 34 year old OEM cable and this homebrew adapter both work well. I did my best to compare to my “reference standard” cable, a Retro Gaming Cables N64 NTSC SCART. To my eyeballs, the signals were the same on this consumer Sony Trinitron. No doubt more scientific tests are needed but for my gaming needs, this new setup works great.