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PostPosted: Wed Aug 15, 2018 7:23 pm 
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I will look at this site, seems to have a lot of interesting information on the subject. I don't know if they talk about Japanese sets yet.

I have been searching for a converter that could have done rf to hdmi so I could have used one of my famiom near my computer but it seems quite uncommon actually in Japan or I do not search with appropriate words in Japanese.

For connecting to my tv set, I could try the composite mod since I have a few junk famicom lying around but the converter would have saved time and allow to use on a PC monitor, which is a plus (the rest of the family don't really "share" much the tv :lol:)

How hard is the composite mod to do for someone that knows how to solder but is have very little knowledge about electronics?


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PostPosted: Wed Aug 15, 2018 7:29 pm 
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Banshaku wrote:
How hard is the composite mod to do for someone that knows how to solder but is have very little knowledge about electronics?

It's a pretty simple construction.

I used this schematic by kyuusaku, and it worked very well for me:
Image

Here's the original thread where I found that: http://www.famicomworld.com/forum/index.php?topic=4713


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PostPosted: Wed Aug 15, 2018 9:11 pm 
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Does this mod also work for the top loader or are things different somehow?


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PostPosted: Wed Aug 15, 2018 9:15 pm 
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It's the same 2C02.

The only possible variability is the amount of impedance-induced hue rotation, where higher gain (i.e. multiple voltage buffers) might (maybe) reduce the amount of differential phase distortion (i.e. where colors $3x aren't the exact same hue as colors $0x)


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PostPosted: Wed Aug 15, 2018 10:20 pm 
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I browsed the thread very fast and it seems that you need to cut the trace for that pin to avoid jailbars in some case. I may have said that it was some junk famicom but what I meant is that I found them in the junk section, which in Japan means "things we didn't even bother to test" :lol:. They seems to be working well it just that cutting trace and maybe breaking things along the way scare me a little bit ^^;;

The diagram with the pin seems to be about the video so I guess there must be something else to be done for the audio. I will continue to read the thread on the subject.


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PostPosted: Wed Aug 15, 2018 10:35 pm 
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You don't need to cut any traces or lift any pins to do that mod. (I didn't.) Everybody seems to report different amounts of jailbars, but I was maybe lucky that they weren't significant for me.

The audio signal just comes straight from the audio return pin on the cartridge connector. Only a wire is needed. (I think some people use a small capacitor in line here, though.)


As for the jailbars, I wouldn't pay any attention to all the weird suggestions people have for that unless you first do the simple mod and determine that it's a problem for you. A lot of the things people suggest for that seem really complicated (desoldering PPU, etc.) or dubious/superstitious.


Last edited by rainwarrior on Wed Aug 15, 2018 10:38 pm, edited 2 times in total.

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PostPosted: Wed Aug 15, 2018 10:37 pm 
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If you're worried about damaging things by cutting a trace, you can instead just desolder the original transistor amplifier or its pull-up resistor (Q1 and R12 on Electronics Junker's schematic) instead.

That's far more reversible.


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PostPosted: Wed Aug 15, 2018 10:39 pm 
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...also, I can't seem to find that image I linked in the thread anymore, which is kind of weird? There is a very similar alternative linked here but it switches the resistor/capacitor components slightly. I'm not sure if this works better/worse, I only tried kyuusaku's diagram.

lidnariq wrote:
If you're worried about damaging things by cutting a trace, you can instead just desolder the original transistor amplifier or its pull-up resistor (Q1 and R12 on Electronics Junker's schematic) instead.

I think some people actually suggest desoldering the original amplifier to use for the transistor in the mod circuit. (I just used a new one, and left everything intact.)


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PostPosted: Wed Aug 15, 2018 10:47 pm 
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So that mod works just by soldering the new circuit in? No need to cut/desolder anything? Every guide I ever saw said you had to cut/remove stuff, which I too am not very fond of.


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PostPosted: Wed Aug 15, 2018 10:50 pm 
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Given Kyuusaku's original schematic, I think you could even just leave the original 2SA937 in place (because it's the same type of transistor and hooked up the same way), and just remove R12. Then add the two new resistors and capacitor.

If you want an even less visible modification, you might be able to bypass the RF modulator altogether and repurpose the RF output jack to emit baseband video instead. Still need a place for the baseband audio output jack, though.


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PostPosted: Wed Aug 15, 2018 11:42 pm 
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While searching about what is a 2SA937 (like I mentioned, I don't know much about electronic yet) I ended up on some Japanese website that one seems to update the mod to improve the jailbar by adding some caps(?) :

http://68000.web.fc2.com/nes_composite/ ... osite.html

And other site which modify the famicom for hdmi instead (maybe this is something already known, I'm quite late in nes news these days):

http://vaot.mydns.jp/fc/hi-def-RWFamicom.htm

the hdmi link came from the author site:

http://vaot.mydns.jp/fc/

Maybe I ended up on something interesting or it is something that everybody knows and I'm just shaming myself by posting obvious things ^^;; If those things were unknown, I can translate some of the content, if necessary. But I guess someone that knows electronic can guess just by looking at some of the hardware used.

edit:

And this page seems to talk about a solution for jailbars on famicom:

http://vaot.mydns.jp/fc/noise5.htm

I'm too illiterate in electronic to confirms the content ^^;; I think I found an interesting site. I would love to know more about electronics first though.


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PostPosted: Thu Aug 16, 2018 1:02 am 
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rainwarrior wrote:
As for the jailbars, I wouldn't pay any attention to all the weird suggestions people have for that unless you first do the simple mod and determine that it's a problem for you. A lot of the things people suggest for that seem really complicated (desoldering PPU, etc.) or dubious/superstitious.

For what it's worth, my simple composite mod on my top loader gives me a better composite image than any regular front loader NES I have seen, free of jailbars. I did the thing where I desolder reuse a transistor used for the RF output.


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PostPosted: Thu Aug 16, 2018 9:39 am 
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Banshaku wrote:
improve the jailbar by adding some caps(?) :
The 2A03 and 2C02 are so-called "mixed signal" devices. "mixed" because they are have both digital and analog portions inside.

Modern "mixed signal" devices have separate power supply pins for the two types of signals, allowing a very clean (without any voltage variation) power supply for analog and a much rougher supply for digital.

But the 2C02 doesn't. Internally, the same 5V are used for both.

A major source of noise is this variation on the 5V line; especially for the 2C02 which has no feedback (and so no power supply "rejection") internally. The video stage is nothing more than a long chain of resistors, and a multiplexer to choose between one of the those voltages.

Adding the capacitors makes the 5V supply "firmer", so that it changes voltage less in response to other devices needing more or less power. This, in turn, means less noise should be visible inside the video output.

Quote:
And other site which modify the famicom for hdmi instead (maybe this is something already known, I'm quite late in nes news these days)
That's kevtris's project.


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PostPosted: Thu Aug 16, 2018 5:52 pm 
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Oh, that's why it looked familiar but didn't know why. Thank you for clarifying that part and the caps one. I always enjoy reading the explanations even though my knowledge is limited on the subject but I'm always grateful about such information.

So the site was nothing new after all. I was just getting exited for nothing but it was fun while it lasted :lol: As for the Kevtris mod, that is something I would have loved to add to one unit since it could be connected later to a pc monitor and with the limited space in Japan, that would have been very useful. But.... After seeing the images on how it was installed... I don't think I can do that.

My old monitor for some odd reason support components cables (not the japanese d-terminal type, the RCA based one) so maybe figuring out a way to convert the signal that way would make more sense even though the quality was not so great when I tried a PS2 long time ago. I will check if there is information about that on the web.


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PostPosted: Thu Aug 16, 2018 6:55 pm 
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The two japanese sites linked seem to advocate very similar solutions.

1. A large, 330uF capacitor on the power rail. The sites differ on whether solid polymer or standard electrolytic is best.

2. Replace .1uF capacitors with 1.5uF capacitors (GPM revisions) or add 2.2uF capacitors (HVC revisions), multilayer ceramic.

3. Cut Pin 21 or eliminate the trace to the base pin on the video amplifier transistor or remove the video signal wire from the board

4. Add a 1nF capacitor across the video and ground lines (optional).

I have read that it is best to add a 220uF capacitor at the audio output pin, to eliminate DC offset perhaps.

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