Super Famicom + RGB cable: mod for RGB|4/3

[Alcahest]

Hey All,
I use a Super Famicom with RGB cable.
Each time i power up the SFC, the tv changes the channel automatically to RGB input, OK but it also changes the Aspect Ratio of the screen to 16/9!
Since it makes no sense that a SFC would force 16/9, i looked around and seem to have found the issue.
Euro TVs are "told" which way to display the input according to Pin 8 on the scart cable:

Select [Pin 8]
0-2V  TV Mode (default) 
5-8V  16:9 Mode 
9.5-12V  4:3 Mode 

The problem comes from there. A Japanese SFC or USA SNES sends only 5 volt to Pin8, which makes the display switch to 16/9.
Euro SNES do not have this problem as they send +12Volt to this pin, so that TV is informed it must display 4/3 alright.

Source:
http://gamesx.com/wiki/doku.php?id=av:nintendomultiav
http://members.optusnet.com.au/eviltim/gamescart/gamescart.htm

With this in mind, is it possible to correct this issue for Japanese SFC/USA SNES by modding the cable?
It's borring to correct the Aspect Ratio back to 4/3 on the TV side every time after switching ON the SFC.
I don't know anything when it comes to electricity, but can the +5v be altered to +12v somehow? or any other tricks you can think of
Thanks for your help.

Alcahest

[NFG]

Have you tried simply unplugging the mode select pin ( or grounding it?  If you put it in "TV Mode (default)" does it switch to widescreen or 4:3?  And, if it's in this mode, perhaps you can change it back with your remote, as you normally do.

[Link83]

I think if you put it in 'TV mode' it would no longer switch to AV1 (The RGB channel) so that would probably makes the situation worse, as you would then have to choose AV1 and choose 4:3 aswell!

Sorry I havent got a solution. I think you may just have to put up with switching to 4:3 mode manually using the remote ....At least it switches to AV1 automatically though!

On a slightly unrelated note, I cannot believe that HDMI doesnt currently support auto-switching as standard like European Scart sockets have done for years 

<EDIT> After having a think, I was wondering if there are any 12V points inside a US SNES that you could connect up to pin 3 of the AV Multi Out? (If you do its probably best to cut the original 5V trace to be on the safe side) I have never tried this and I dont know if it would work but it should do?

Alternatively I guess if there is no 12V point in the US SNES you could get a 12V battery pack/power supply and open the scart cable, remove the wire currently going to pin 8 and connect this extra power to it? Seems like alot of work though just so you dont have to press a button on the remote! (Even though I know how annoying it is)

Please note I havent tried either of these mods - im just guessing that they 'should' work.

[viletim]

Alcahest,

The PAL SNES uses some kind of capacitor charge pump circuit to generate approx +12v scart switching voltage from its 5 volt rail.

You could put a 9 volt battery in series with the 5 volt rail to get 14 volts. That'll switch the TV over - at least till it goes flat.

[Alcahest]

Hello guys,
thank you so much for your fast answers.

> Have you tried simply unplugging the mode select pin ( or grounding it?  If you put it
> in "TV Mode (default)" does it switch to widescreen or 4:3?

Yes, if i disconnect pin 8 and leave pin 16 connected, I must go to the AV channel manually, it displays RGB alright and 4/3, all good. But it doesn't autoswitch to that channel anymore, which is handy ^^

> Sorry I havent got a solution. I think you may just have to put up with switching to 4:3
> mode manually using the remote ....At least it switches to AV1 automatically though!

That's right. Either i leave pin8 connected and must correct 16/9 or remove pin 8 and must switch to RGB channel manually.

> On a slightly unrelated note, I cannot believe that HDMI doesnt currently support auto-
> switching as standard like European Scart sockets have done for years

Yup, that stroke me as well. But it's a sony marketing scheme it seems.. later Bravia tv models and sony equipment (ps3), have what's called "theatre mode", which will detect sony equipment upon startup and swith to the right tv channel automatically.
In other words, they're selling what used to be free, auto-switching. :/

> Alternatively I guess if there is no 12V point in the US SNES you could get a 12V battery
> pack/power supply and open the scart cable, remove the wire currently going to pin 8
> and connect this extra power to it? Seems like alot of work though just so you dont have
> to press a button on the remote! (Even though I know how annoying it is)

> The PAL SNES uses some kind of capacitor charge pump circuit to generate approx +12v
> scart switching voltage from its 5 volt rail.

We have the answer right there

> You could put a 9 volt battery in series with the 5 volt rail to get 14 volts. That'll switch
> the TV over - at least till it goes flat.

Is there no other ways before resorting to this? this capacitor charge pump circuit, depending on how hard it is to reproduce, sounds like it could do the trick?

Later,

Alcahest

[albino_vulpix]

You've got nothing to complain about :p

Not only does my TV not auto-switch, an image with no sync appears on every other channel.
So if I'm playing Mega Drive or Wii, can't flick to another channel.

[viletim]

> Alternatively I guess if there is no 12V point in the US SNES you could get a 12V battery
> pack/power supply and open the scart cable, remove the wire currently going to pin 8
> and connect this extra power to it? Seems like alot of work though just so you dont have
> to press a button on the remote! (Even though I know how annoying it is)

> The PAL SNES uses some kind of capacitor charge pump circuit to generate approx +12v
> scart switching voltage from its 5 volt rail.

We have the answer right there

> You could put a 9 volt battery in series with the 5 volt rail to get 14 volts. That'll switch
> the TV over - at least till it goes flat.

Is there no other ways before resorting to this? this capacitor charge pump circuit, depending on how hard it is to reproduce, sounds like it could do the trick?

You won't be able to reproduce the Nintendo circuit, it uses part of some custom chip.

Maybe this will do the trick: +5v to +13v Converter

albino_vulpix,
Once you get used to auto-switching it's very annoying to go with out it. It's a feature which should have been built into all TVs ever since A/V devices were invented! At least the europeans got it (half) right.

[Alcahest]

You've got nothing to complain about :p

Not only does my TV not auto-switch, an image with no sync appears on every other channel.
So if I'm playing Mega Drive or Wii, can't flick to another channel.

If you have a Sony TV, go in service mode and set "RGB Priority" to OFF.
Worked for me on my old trinitron
With this i could have RGB source working and still see the other channels OK.

[Alcahest]

You won't be able to reproduce the Nintendo circuit, it uses part of some custom chip.

Maybe this will do the trick: +5v to +13v Converter

Wow very nice, but i fear way too complex for my skills ^^;
I think i'll settle for the 9v battery trick, or i may just remove pin8 and switch to RGB input manually, it's 1 step less than switching manually to 4/3 on my tv.
Thanks again a lot guys, and kudos to Lawrence for his excellent site.
Later,

Alcahest

[marqs]

Why not try to take the ~10V directly from sfc's power supply? I don't know if it's capable to drive the extra power though (and is it over 9.5V under load?).