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PostPosted: Tue Oct 07, 2014 3:38 pm 
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When I see a high frequency, I try to relate it to known frequencies in the system. Here, 1340 kHz is one-fourth of the 5370 kHz dot clock of the NTSC NES and Super NES PPU. Are the wiggles spaced about 4 pixels apart?


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PostPosted: Tue Oct 07, 2014 4:10 pm 
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Hmm. Did you really submerse it?

I think the only real reason fully covering it in water/alcohol can be a step above q-tipping it is because you can flush out all the little areas you can't get to, under chips and whatnot. I sort of feel like I'm just pushing dirt around with alcohol sometimes. I'd imagine if you brush the area next to a chip the alcohol will spread out under the chip and then evaporate, leaving some crud behind. No scientific evidence here though just a vibe. And dirt doesn't always cause a problem, it can be a shot in the dark.

I've seen non-working macs start working, no-sound macs suddenly have sound. But those have so many interference problems, some people get one and recap it before they even turn it on. Just a more complex board or something. You're more likely to get results when you've got so many problems on one board I bet. Your NES has 1 minor problem whereas the stuff I did this on had quite a few minor and major problems. So I guess your chances of success would be lower.

I did once have this sort of problem on a genesis and it ended up being mostly due to a bad voltage regulator. If I recall, it seemed to put out the right voltage when I checked it with a multimeter but I had no scope to look at the waveform. I changed it anyway and it did come out better. Though not perfect until I changed the caps.

If nothing else at least if you've gotten away with putting water on it. I sure felt better when I realized you can be a little rough with circuit boards.

Btw if you're thinking about recapping but you're still a bit scared to do it you can always find some board you don't need from somewhere and practice on that. The two things I watch out for when I remove caps is holding the iron way too hard on a via and then it just lifts off with the solder like it wasn't attached in the first place, or pulling too hard on a lead as I'm desoldering. If the solder hardens while you're pulling it out you can rip off a trace pretty bad that way. But if you're gentle and back off of a via when it's not melting for some reason rather than grinding the iron into it, you should be fine. My soldering iron is pretty bad but I've never ruined a board or even a single trace/via except when I'm trying to recover a chip with no regard for the board it's on.

I just have such a strong distrust of capacitors after all this mac business. I feel like it's hard to narrow these kinds of problems down if you haven't recapped. So many things could happen but bad capacitors eventually always happen. They're so likely to go that the second I see something like this I usually think about recapping the board. The NES, again, is some kind of magic for even working this long. I know in some cases capacitors are absolutely necessary and some are just extra insurance for clean power that the board will work without. Maybe some of them just aren't that important on the NES. I'd be interested to know why it's not such a problem on the NES if anybody knows.

Anyway, sorry for all the capacitor rants. haha.


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PostPosted: Tue Oct 07, 2014 4:11 pm 
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tepples wrote:
When I see a high frequency, I try to relate it to known frequencies in the system. Here, 1340 kHz is one-fourth of the 5370 kHz dot clock of the NTSC NES and Super NES PPU. Are the wiggles spaced about 4 pixels apart?

Interesting! That looks about right to me (roughly 3-4 pixels) when looking at the initial screenshot (which isn't the OPs, it's just an example he found).


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PostPosted: Tue Oct 07, 2014 4:12 pm 
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Caps do suck, even today. Most cheap PSU's buy cheap caps that dry QUICK because they're POS's, causing tons of failures. Any discount computer or PSU probably uses those caps, unlike my corsair 950 watt desktop PSU, which uses solid caps. :)


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PostPosted: Tue Oct 07, 2014 4:23 pm 
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tepples wrote:
When I see a high frequency, I try to relate it to known frequencies in the system. Here, 1340 kHz is one-fourth of the 5370 kHz dot clock of the NTSC NES and Super NES PPU. Are the wiggles spaced about 4 pixels apart?
Yeah, they are. The problem is that they're not at a constant phase relative to the pixels, which they should be if it's noise directly generated by the PPU.


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PostPosted: Tue Oct 07, 2014 8:42 pm 
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For a better point of reference, this is a screencap from my own system. This was from the first motherboard, before I swapped it with the second one, but, the results are largely the same.

Image


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PostPosted: Tue Oct 07, 2014 8:52 pm 
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Probs the TV PSU. Keep the NES on, turn the TV on and off a lot.


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PostPosted: Wed Oct 08, 2014 4:28 pm 
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So, I'm finally going to bite the bullet and try replacing the main cap in the RF mod - the 2200 uF/25 volt one.

In case I can't find an exact match, is there any other spec I can use that's compatible?


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PostPosted: Wed Oct 08, 2014 5:13 pm 
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Higher capacitance and/or voltage rating will be fine, maybe even preferable. Just don't go lower. Dimensions-wise, a newer capacitor of the same rating will be much smaller than that old one. If you have a choice, I would go with decent low-ESR caps like Nichicon HE series, or Panasonic FC series.


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PostPosted: Wed Oct 08, 2014 5:15 pm 
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I'll see what I can find at RadioShack. I'm reading elsewhere that apparently the back of the RF mod just pops off without having to desolder it from the circuit board. Is this correct?


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PostPosted: Wed Oct 08, 2014 5:19 pm 
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Yeah, the cover pops off. Desoldering the RF box itself is a pain, it takes a lot of heat.


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PostPosted: Thu Oct 09, 2014 8:34 am 
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Well, the only appropriate capacitor at RadioShack they had available had one the pins on either side, so, it's not exactly like the one that's in the NES. I don't know if this is even going to fit in... it certainly won't fit in that hole that's in the RF mod because it's going to lay horizontal instead of vertical and even if it can lay horizontal, I doubt the pins are long enough as they are. Can I still use this cap or should I order online something else?


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PostPosted: Thu Oct 09, 2014 10:55 am 
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Bridger wrote:
Well, the only appropriate capacitor at RadioShack they had available had one the pins on either side, so, it's not exactly like the one that's in the NES.
In that case, I'd look for one with higher values that would fit better. The values of the capacitor aren't too important, as long as they're at least as much as the original 2200uF and 25V.


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PostPosted: Thu Oct 09, 2014 11:23 am 
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I thought the rule of thumb was same capacitance, same or higher voltage. Just in case a capacitor is filtering something specific only. I know you can generally get away with higher capacitance but is there no scenario where higher capacitance would mess with the original intended function of the capacitor? Like in the case of something like a high/low pass filter?


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PostPosted: Thu Oct 09, 2014 11:43 am 
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The huge capacitor there is a power supply filtering one. Larger is ok, as long as the equivalent series resistance (i.e. maximum instantaneous current) doesn't go up (down) too much. (It probably won't)


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