Snes scart lead noise?

[paulcan69]

Hello All,

Thanks Ace' for my awesome modded snes it's getting some love tonight, I have a RGB scart lead which works fine but like probably all cheap scart leads I get feedback screen noise as the picture gets brighter, same as my megadrive which I think also came with a cheap scart lead.

B.T.W Ace' didn't supply this lead as I purchased "unit only" from him, just I had this with another snes.

The picture is perfect but it always has this buzzing/hum noise and it gets louder when the picture gets brighter and more busy.

I don't really want to buy another snes scart and another megadrive scart, I want to try to fix them, some caps or resistors maybe?

It's not my setup, as I run loads of consoles on this TV and lots of them with RGB scarts but they are all £10-£15 ones (nice ones) my megadrive and my snes ones are £5 max jobbies.

(Plus I have tried other TV's and setups)

Could this all be down to the sheilding of the lead itself?

In other words I'll never fix it without buying better cables?

Or your advice on things to try please?

Thanks in advance!
paulcan692011-01-15 22:15:38

 

[Ace`]

Hi Paul,

You need to open up your scart lead and see if it has any caps on the rgb lines, if it has you will need to remove them as shown here http://www.mmmonkey.co.uk/console/nintendo/pal-snes-rgb.htm

HTH Paul.

 

[paulcan69]

Hello mate, I did check just that tonight and no caps, I can see one resistor, can't remember the value but can check it to see if it's the wrong one?

 

[Ace`]

Sounds like you'll need to add resistors to the rgb wires, have you tried a composite cable?. I know composite isn't as good as rgb scart but I used a composite on a 40" lcd and it looked surprisingly good.

 

[paulcan69]

What value would you try Sir?

Also yeah I will try composite and see + report back.

 

[trm]

In the absence of better (i.e. tested) info on what resistors to use, try something between 220R and 470R (R=Ohms). I'd put these on the RGB lines initially and leave sync alone. If you find you've still got issues then try a same value resistor on the sync line.

It sounds like the SNES is over-driving the inputs to the TV. If you can get a good photo of the noise/interference then that'd be useful.

cheers

tim

 

[trm]

Also, I don't recall whether you've got a scope yet or not. If you have, scope one of the colour lines on 5V/div and whatever timebase you need to get a stable beam you can measure. If at 5V/div the trace is almost at zero point then switch to 1V/div and measure the number of divisions between the baseline (the default beam position) and the maximum deflection of the beam. That'll give you the Peak-to-Peak signal levels that the SNES is outputting. Most home TVs only like 0.75V P-P which means that on a 5V/div setting you shouldn't see much activity from the SNES, but if you do then it's overdriving the TV.

Various options once we've narrowed it down - you will have high quality (well, until you display it on a 40" screen

) SNES gameplay!

 

[paulcan69]

The picture is frecking awesome!! Spot on, nice and bright but not too bright!

No interference to the actual picture, just humming noise which gets louder or quieter depending on amount of graphics and or overall brightness on the screen.

For example Zelda as you boot the cart it's all black screens, even the first part of the title screen, the noise is there but so quiet you almost can't hear it, but if for example a very white bright screen screen comes on the noise gets louder, at first I thought I could cope with it but now after 1/2 a day of playing on it no way.

Same goes for my megadrive lead really so most keen to see if this works.

I have got a load of 470 ohm resistors so I think I'll try that first.

Thanks Tim, and sorry no scope yet but shall keep my eye out for one.

I will try on the rgb lines first then onto the sync line, ta bud.

P.S I could shoot a video I'm sure it would pick it up if I cranked the tv volume up to the max
paulcan692011-01-16 20:45:36

 

[paulcan69]

By the way I still have various 25", 28" crt 4:3 tv's, it's the only way to play retro games.

Various makes, Sony, Mitsuishi, JVC, Panasonic it does this on all of them, same with my megadrive, I'm guessing it's a cheap lead problem.

My psx/ps2 blaze rgb lead (factory made) is the nuts, no bleed of noise through the speakers at all + it has 2x rca's which I push through and old Sony stack system and it sounds great.

So that's what I use for retro stuff, I keep it as old skool as possible to stop other issues which may arise from adding modern TV's etc...
paulcan692011-01-17 21:19:58

 

[trm]

Ahhhhhhhhhhhhhhhhhhhh.

I didn't realise that when you said "noise" you meant audible noise. I thought you were talking about a noisy image. Too much time spent geeking with video

.

The more obvious reasons for noise will be crosstalk between conductors, mains hum being induced in the cables, poor signal isolation on the source end and so on.

So is it fair to see that a black screen is nice and silent, but a full bright white screen causes a nice hum? Can you capture the hum - could be mains 50Hz bzzzzzz.

A super quick fix could be to wrap the cable through a ferrite core in case it is induction causing the problem, but I suspect it could be a bit of a ropey (i.e. cost-saving) video design on the mobo which means insufficient screening and grounding is in place

cheers

tim

 

[DanP]

I had no idea you could do that to a Snes. What's the picture quality like? Is it a difficult conversion? Got a stack of Snes stuff in my loft

Dan

 

[paulcan69]

Will do I'll post a video later.

Dan the picture is soooo good, snes puts out RGB as standard so no mods needed just a "decent" cable, the picture is perfect, I know that if I had a better cable it wouldn't do this, same as my megadrive.

Be warned though, you do need to wire it for a pal snes or a ntsc snes, as far as I know they do have different pinouts, do some reading on this.

Like I say picture is uber good, just need to lose this humming noise.

Thanks,

 

[paulcan69]

Just for info this is a pal snes with a 50/60hz mod via the reset button, I will try my other snes which is normal to prove it's the lead and report back with a video

 

[paulcan69]

Right "hear" goes....

Notice you can hear it slightly from the beginning but it does get bad when you press start button and the items menu drops in, even when Link walks outside and the screen goes blank you can hear it stop for a second then it returns as outside loads.

It does do this on other games, just as bad but all do it under slightly different conditions, i.e sometimes when it's bright, but I think it's related to how many pixels are in use at one time on the screen if that makes sense, don't laugh at my bad description

I tried the same lead on my normal snes and that's the same so 100% the lead, I think it's just cheap, tempted to just buy another and one for my megadrive as well but would be nice to know if I can fix it just so I know what people do wrong when they build these leads??

It's worse when I put the camera closer to the tv so you can hear it more, but as a person I can hear it louder than you can record it.

DanP check out the picture close up, you can see it's waaayyy better than using RF or comp, snes rules with it's RGB as standard.

Pal N64's don't do it, Gamecube's do.

NTSC 64's can do but you still have to mod them.

Thanks for looking!!

[tube]sMiKRBr2QUc[/tube]
paulcan692011-01-17 19:29:36

 

[trm]

Sounds to me like you've not got screening between the video and audio cables. When I used to make my own SCART or S-Video leads I'd buy specific cable that had a mylar coated polyester ribbon that wrapped around the individual wires within the cable and tied to ground to stop crosstalk.

Not sure how much you fancy hax0ring this, but it would be interesting to see what happened to the audio if you disconnected the RGBS wires at the SNES end and ran the game. Given that no signal will be transmitting down the RGBS wires, there'll be no chance of crosstalk to the audio wires. If the noise is diminished when you do this, then it'll almost certainly be fixed by using properly screened & shielded cables.

Note that the noise will probably only drop and not disappear because you'll then have the RGBS wires on the SNES end acting like aerials and picking up any AC50Hz hum around.

cheers

tim