Super Famicom corrupted video output

[DaveJ-UK]

I bought a Super Famicom (aka Japanese SNES) from the bay.

The guy claimed to have lost the AV cable and was therefore selling it as untested. In hindesight, I should have seen that this is blatantly bullshit - turns out the video output is corrupt. I think it's reasonable to assume he knew this. Bastard.

Being the adventurous type I am, I'm going to have a stab at repairing it. I've been under the hood of a PAL SNES on a number of occasions to do the region mod and 50/60Hz mod. However I don't even know where to start with this video issue and it's not exactly the easiest topic to Google on.

The game plays and you can see what's going on but there's a purple and green horzontal bar that scrolls from top to bottom. When it gets to the bottom it disappears for a second, there's a small pop on the sound, the screen flickers, then it appears again at the top. I've tried it with several games and it's exactly the same.

If it was a monitor I'd say it needed a cap kit!

Any help greatly appreciated!

[kendrick]

Dave, do you get this same weird, travelling horizontal bar in RF, composite, S-video and RGB? It's worth figuring out of the bar is isolated only to one of those output types (which would indicate an encoder problem, or a signal noise issue) or if it's present on all four (which might indicate some kind of digitization problem that occurs prior to video encoding.) If it's the former, it might not even be worth fixing if you can make use of the other formats. If it's the latter, you might not be able to fix it short of an IC swap.

And now, Tim will be along to remind us that he's ten times smarter than I am when it comes to video signals. :)

-KKC

[viletim!]

DaveJ-UK,

From what you've described, I'd be inclined to point the finger of blame towards the power supply. Does the bar take about 4 seconds to get from the top of the screen to the bottom? If this is the case it's likely the source of your noise is your mains power (which would be 50Hz in the UK) which is manifest as a scrolling bar on your Super Famicom's (60Hz) video output.

How is the unit powered? The PAL and NTSC NES require different types of power supply (one wants DC voltage, the other AC), so if you're trying to power it if with a localy bought SNES power supply then you'd better check that it's suitable.

[NFG]

Seems to me the connectors on a PAL, JP and US SuperNES are different, but the voltages are the same.  Like viletim I too would blame the power supply, the fact that it 'pops' indicates a power problem somewhere.

[FM-77]

Seems to me the connectors on a PAL, JP and US SuperNES are different, but the voltages are the same.

Actually that's not entirely correct.

PAL 9V, 1250 mA
NTSC 10V 850 mA

I tried using a PAL adaptor on an NTSC SNES once and I encountered the same problems DaveJ-UK did.

[DaveJ-UK]

Thanks for the great response guys. This sounds encouraging - hopefully it's not the console at all.

I am indeed using a UK power supply which would have originally shipped with a PAL SNES.

I haven't tested it with anything except RF - I should have thought of that one really.

And yes, it takes about 4 seconds from what I remember.

I'll have to dig through my box of power supplies for a more appropriate supply. I would have assumed a Japanese SNES had the same power requirements as a UK model and since it came with one, it didn't even occurr to me to check.

I'll keep you posted. Thanks again.

[DaveJ-UK]

I've only just had a chance to test this with another PSU and the results are encouraging.

From Seldane's post, I understand that a Japanese Super Famicom requires 10V/850mA/centre-negative

The original issue I described was with a UK SNES PSU.

I tried it with a Jaguar 64 PSU (!) which is 9V/1.2A/centre-negative. This is MUCH better although if you look closely you can still see the scrolling bar, although it just looks like a dark patch rather than funky purple/green.

[blackevilweredragon]

my american snes is always noisy, even via svideo

[RobIvy64]

Dave, see if a Mega Drive power supply fixes the problem (Mega Drive model 1).

I have a Super Famicom and this PSU works perfectly for me.

[CZroe]

I just want to add for the record that my US model 1 Sega Genesis plug seems to work fine also, but I am concerned about the increased amperage and I am looking for the correct specs. Also, when someone says that the "tip" is negative or positive, do they mean the outer sheath or the pin inside? It seems like the terminology was coined for the less-common kind with similarities to a headphone connector.

[DaveJ-UK]

I just want to add for the record that my US model 1 Sega Genesis plug seems to work fine also, but I am concerned about the increased amperage and I am looking for the correct specs. Also, when someone says that the "tip" is negative or positive, do they mean the outer sheath or the pin inside? It seems like the terminology was coined for the less-common kind with similarities to a headphone connector.

As long as the power output (A) of the supply matches or exceeds the requirement of the device it's powering then it's fine. The console will only pull the power it needs. However you should always ensure that both the Voltage and Polarity (+/-) match. Sometimes you'll get away with a slightly different Voltage but don't count on it.