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PostPosted: Tue Mar 05, 2013 5:29 pm 
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I've dug through several threads on the internet from the Assembler and Sega forums and nothing solid has been found about it other than it doesn't affect all SNES revisions. It's not caused by faulty power supply or interference from other devices on the same power grid. It occurs no matter what video output you use RGB/S-Video/Composite. It may be a design flaw in some of the SNES's. Sometimes the bar has a yellowish tint to it (one of my SNES's does).

For those that don't what the vertical line is, basically it's a fairly thick band that is smack dab in the center of the screen. It's most prominent on dark areas and can be seen very well in the FF3/FF6 intro and in Super Metroid when Samus is exiting her ship after the intro.

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So has anyone done any further research on this. I figured this would be the best board to ask seeing as there are so many hardware tech savvy fellows abundant here. I'm really curious what the underlying problem is that causes this, if it's the PPU, or the video encoder, or whatever. I have a SNES-001 that has it pretty bad with a yellow tint that has a BA6592F encoder, another SNES-001 with a S-ENC chip that doesn't have it and a SNES 101 (mini) that also does not have the bar.

Any ideas?


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PostPosted: Tue Mar 05, 2013 6:16 pm 
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Is that bar the DRAM refresh time?


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PostPosted: Tue Mar 05, 2013 7:05 pm 
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It may be worth pointing out that I have seen before a very similar line on the very right side of the screen in some of the border area.

It may correlate with power draw or line stability as well. My SNES with the new power supply I have installed internally shows very little to no bar; I notice it on my SFC now that I've switched from that SNES. Some SNES revisions have a spot for a pretty large capacitor on the DC in jack where it is not populated.

Edit: From looking at that Super Metroid screenshot, I think it definitely comes from spikes in power draw and not from interference from other lines like the Famicom/NES vertical jailbars; it is lighter for a length, then comparably darker, before settling to the brightness it was before, suggesting power consumption that looks somewhat like so:

Image

Please excuse my laptop drawing skills


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PostPosted: Tue Mar 05, 2013 7:43 pm 
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It's been proven that replacing the capacitors on the SNES PCB does not have any effect the visibility of the bar unfortunately. I've dried different AC adaptors on my SNES with the problem, 2 official and a quality universal that I recently purchased and it doesn't show any sort of difference on the visibility of the bar, it's just always there.

Tepples: I'm unsure what you mean by your question. I'm not too familiar with SNES hardware and to be honest, have no idea what DRAM is.

Here's my SNES in particular at the bootup of FF3 and title screen. It's faintly visible in the picture at the title screen, but clearly visible in person. The bootup picture you can see it very well:

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PostPosted: Tue Mar 05, 2013 8:19 pm 
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The SNES uses DRAM memory instead of static RAM, to save cost. DRAM requires regular refreshing of the contents before it fades. The SNES does this refresh in the middle of each scanline, thus the theory that it could be the cause. I've seen this on several of my SNES units, though it's quite light. It seems plausible that it's something in one part (like DRAM refresh) spilling over into another due to imperfect isolation (power supply droop, RF coupling) between the video section and somewhere else. The source of the interference is related to scanline timing, since it occurs consistently on each one. It would be very interesting for someone with a scope to see whether there's a corresponding disturbance in the 5V power rail.


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PostPosted: Tue Mar 05, 2013 8:38 pm 
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Did all models of SNES's use DRAM? Would that explain why some are affected and some aren't? Or maybe a low quality DRAM was used on certain revisions...would their position on the board have any impact?


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PostPosted: Tue Mar 05, 2013 8:41 pm 
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blargg wrote:
The SNES uses DRAM memory instead of static RAM, to save cost. DRAM requires regular refreshing of the contents before it fades. The SNES does this refresh in the middle of each scanline, thus the theory that it could be the cause. I've seen this on several of my SNES units, though it's quite light. It seems plausible that it's something in one part (like DRAM refresh) spilling over into another due to imperfect isolation (power supply droop, RF coupling) between the video section and somewhere else. The source of the interference is related to scanline timing, since it occurs consistently on each one. It would be very interesting for someone with a scope to see whether there's a corresponding disturbance in the 5V power rail.


I have neat old scope, when I get home I could see if there's any regular fluctuation in the 5V line. What would I want to compare this to? Is there an obvious point that will oscillate during HBLANK?

Pasky wrote:
Did all models of SNES's use DRAM? Would that explain why some are affected and some aren't? Or maybe a low quality DRAM was used on certain revisions...would their position on the board have any impact?


A more important question to me is can the DRAM be replaced with superior but compatible RAM?


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PostPosted: Tue Mar 05, 2013 8:50 pm 
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The DRAM is in the chip. Good luck replacing that. But still, anyone willing to start hooking up bigger caps to their system?


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PostPosted: Tue Mar 05, 2013 10:34 pm 
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DRAM consumes drastically more current during refresh than normal read/write operations. So if that's when it's refreshing DRAM it is pretty probable that's the culprit. Replacing caps apparently didn't help.

Like 3gen said you might try hooking a low ESR large capacitor as close to the DRAM as possible (apparently that means the CPU since I think 3gen is saying it's part of the CPU's die.

Not sure what the SNES has for a power supply. I'm guessing it's a linear reg. One might investigate using a better power supply and see what happens. You could test with a typical CPU power supply before trying to permanently replace the original.

If the DRAM refresh current is the culprit your only real solution is a better power supply can more (better, low ESR) caps.

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PostPosted: Tue Mar 05, 2013 11:41 pm 
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infiniteneslives wrote:
Not sure what the SNES has for a power supply. I'm guessing it's a linear reg.


The power brick provides 10v, 850mA. I'm guessing it's not too well regulated. Internally, the console does indeed use a linear regulator. A 7805 connected to a huge heat sink, in fact. You could probably save power, reduce the heat, and provide more current in the process by switching to a drop in DC-DC converter replacement.


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PostPosted: Wed Mar 06, 2013 2:11 am 
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When I get a bit more disposable income, I'd be willing to guinea pig some power options (starting with adding caps I suppose). Although I'll need some suggestions on what to do as I'm nowhere near the technical level of some of you.


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PostPosted: Wed Mar 06, 2013 3:02 am 
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That mysterious bar's been driving me nuts lately, too. :roll: Even more so because I can't for the life of me remember seeing it as a teenager back in the 90s. My assumption is that modern TV sets are much more susceptible to slight (power-related) changes in the A/V signal. (I noticed that the bar is more distinctly visible with special hardware like the SNES PowerPak than with regular game cartridges.)

To verify, I hooked up one of my PAL consoles (that clearly shows the bar on my 2004 Loewe 16:9 CRT) to a 1994 Sony Trinitron just the other day -- and behold, the bar was gone. :o

I'll try the same console with my parents' even older CRT next weekend, and report back.

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PostPosted: Wed Mar 06, 2013 5:02 am 
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Oh, I am so relived !!
I really thought this bar was a problem specific to my SNES, and yes, for all theese years. Apparently it's not ^^


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PostPosted: Wed Mar 06, 2013 6:55 am 
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Wow, just the other day I got myself a SNES Jr. (SNS-101) and this line was very noticeable, so I figured it was some kind of malfunction. It's mostly visible in black screens, I can hardly see it during normal gameplay. I have 2 original model SNES's that don't have this problem, at least not as apparent.


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PostPosted: Wed Mar 06, 2013 8:37 am 
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If it's something that degrades with time it's most likely due to the aging of the power supply and especially the caps. Possible that the DRAM could be increasing power consumption over it's life, but a less likely to be this drastic.

My SNES jr. doesn't have the issue but I bought it new in 1996, it really hasn't been played much though. I've got a stack of SNES's out in the garage that I never took the time to test out or try to fix the broken power plug. If no one else is actively making efforts to try a new power supply I might see if I can find a SNES with the problem and try to fix it.

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