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 Post subject: Correct Famicom AV mod
PostPosted: Wed Oct 02, 2013 9:36 pm 
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So I wanted to perform the AV modification on my Famicom. Google led me to a few different places with quick hacky mods and all of them seemed to have to deal with the jailbars and the infinite number of ways to possibly fix them. I decided to ask the master himself (kevtris) and get the best solution. He said to do it the way Nintendo did it. After searching for the NES schematics and checking them out, I began building my mod. After a few days of working and frustration, I got it working without the jailbar problem. It uses more components but the picture quality is nice. I have traced the NES schematics and included the relevant information in my attachment.

A little explanation about the schematic. First off, this is the first thing I have made with Eagle, I'm just learning it. The inductor is labelled as 'MISC15' and its value is 3.3uh. The three things on the left (H1, H2, and H3) are outputs from the Famicom. 5v, Pin 21 of the PPU, and Ground. The ones on the left (H4 and H5) are the leads going to your TV. All capacitors are ceramic.


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File comment: Schematic
famicom-av.png
famicom-av.png [ 155.66 KiB | Viewed 7237 times ]
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PostPosted: Wed Oct 02, 2013 11:07 pm 
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Eagle has export scheme into the picture. There is no need to print screen.


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PostPosted: Thu Oct 03, 2013 12:13 am 
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Are you sure your R1 should be 510? according to the schematic I have it is 150.
Image


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PostPosted: Thu Oct 03, 2013 12:44 am 
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I think there is supposed to be a 10µF electrolytic capacitor in between where the emitter of the left transistor (2SA937) meets a 330Ω resistor (negative side facing the transistor).


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PostPosted: Thu Oct 03, 2013 1:02 am 
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In simulation, the gain is entirely immune to a factor of 4 change on the value of R1. This makes sense, because it's a common-collector amplifier (voltage buffer) and the voltage above the transistor should be one diode drop above the voltage out of the PPU.


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PostPosted: Thu Oct 03, 2013 7:44 am 
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Let me begin by thanking you guys for your feedback, it is much appreciated.

The schematics I used was the buggy Electronix Corp ones for the NES-001. I do not doubt there are errors, but I have found using this method described works. The 10uf electrolytic capacitor right before the 330ohm resistor causes no video output, so I just omitted it. I do not know how it works. I haven't disassembled my NES (again) to check the schematic. Last night I traced the Twin Famicom's AV circuit, and I will be attempting it next. I have attached it here. D1 is mis-labeled because I cannot identify the diode part number.


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twin-av.png
twin-av.png [ 4.79 KiB | Viewed 7205 times ]
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PostPosted: Sun Oct 06, 2013 7:04 am 
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As a suggestion you could go for the standard "hamburger"(as fast food style) kind of Schottky diode, "the legendary" 1N4148. That would be the "right diode" to use there.


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PostPosted: Mon Oct 07, 2013 8:12 am 
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So what I have done now was replace the power/RF board from the famicom with a new power supply and I have used the Twin Famicom AV circuit. I pulled my video directly from PPU pin 21. The picture is good. The diode I ended up using was a Panasonic MA2C029W. The characteristics seems to fit, and the diode looks just like the one in the Twin Famicom. More images can be found at http://nesemu2.com/images/fammod/


Attachments:
2013-10-06 23.50.29.jpg
2013-10-06 23.50.29.jpg [ 1.48 MiB | Viewed 7044 times ]
2013-10-06 23.25.32.jpg
2013-10-06 23.25.32.jpg [ 1.64 MiB | Viewed 7044 times ]
2013-10-06 23.24.43.jpg
2013-10-06 23.24.43.jpg [ 1.43 MiB | Viewed 7044 times ]
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PostPosted: Mon Oct 07, 2013 6:39 pm 
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deadbody wrote:
So I wanted to perform the AV modification on my Famicom. Google led me to a few different places with quick hacky mods and all of them seemed to have to deal with the jailbars and the infinite number of ways to possibly fix them. I decided to ask the master himself (kevtris) and get the best solution. He said to do it the way Nintendo did it. After searching for the NES schematics and checking them out, I began building my mod. After a few days of working and frustration, I got it working without the jailbar problem. It uses more components but the picture quality is nice. I have traced the NES schematics and included the relevant information in my attachment.

A little explanation about the schematic. First off, this is the first thing I have made with Eagle, I'm just learning it. The inductor is labelled as 'MISC15' and its value is 3.3uh. The three things on the left (H1, H2, and H3) are outputs from the Famicom. 5v, Pin 21 of the PPU, and Ground. The ones on the left (H4 and H5) are the leads going to your TV. All capacitors are ceramic.

Huge circuit, lots of filtering, blury picture as result.


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PostPosted: Mon Oct 07, 2013 7:14 pm 
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80sFREAK wrote:
Huge circuit, lots of filtering, blurry picture as result.
What are you talking about? Any circuit that doesn't kill chroma in a composite signal isn't going to appreciably blur the luma.
Anyway, I tried his circuit in sim; it has no appreciable lowpass effect. The -3dB corner is at 100MHz.


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PostPosted: Mon Oct 07, 2013 10:13 pm 
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No blurriness. Just some visible dot crawl. It was blurry because of some camera related problems. Here is some new pictures. Don't believe me? Build the circuit and see for yourself! I been running it on a 50-something inch LCD television.

The output looks identical to my twin famicoms video output. Same circuit same results. I decided to use this circuit instead of the "two resistor and a cap" circuits I've seen floating around the internet. This one has been tested and works on millions of televisions world-wide.

Also I would like to take this opportunity to thank the members of #nesdev. Without them I wouldn't be doing anything like this.


Attachments:
2013-10-07 23.40.35.jpg
2013-10-07 23.40.35.jpg [ 1.25 MiB | Viewed 6994 times ]
2013-10-07 23.40.10.jpg
2013-10-07 23.40.10.jpg [ 1.48 MiB | Viewed 6994 times ]
2013-10-07 23.38.20.jpg
2013-10-07 23.38.20.jpg [ 1.56 MiB | Viewed 6994 times ]
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PostPosted: Tue Oct 08, 2013 6:27 am 
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lidnariq wrote:
80sFREAK wrote:
Huge circuit, lots of filtering, blurry picture as result.
What are you talking about? Any circuit that doesn't kill chroma in a composite signal isn't going to appreciably blur the luma.
Anyway, I tried his circuit in sim; it has no appreciable lowpass effect. The -3dB corner is at 100MHz.

Oh, good :lol: Everything is on the last photo :lol: Keep simulating and emulating, i've gotta go. All the best... :lol:


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PostPosted: Tue Oct 08, 2013 11:48 am 
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His pictures show far improved quality over your "correct" modifications shown on FW and substantially less jailbars. Are you dense?


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PostPosted: Tue Oct 08, 2013 4:14 pm 
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I haven't seen 80sFREAK's pictures, but deadbody's mod lokos fine to me. The pictures are a little blurry, but thats just the photos I think. (Granted you'd need better pictures to accurately judge it)


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PostPosted: Thu Apr 20, 2017 8:37 pm 
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Location: WhereverIparkIt, USA
Well I've had this thread bookmarked forever, and finally got around to performing the twin famicom video circuit mod to my original famicom. My primary motivation came from recently upgrading to a commodore 1702 monitor which lacks the RF tuner I made do with on my previous CRT.

Just wanted to share that this circuit worked great for me as well. For others looking to follow along, I also found some new transistors readily available from Digikey that worked well for me. I also used the 1N4148 as l_oliveira suggested.

Analog, video, and BJT's are far from my expertise, but I searched around and found the KSA1015 has comparable specs to the 2SA1015, and it's compliment KSA1815 looked comparable to the 2SC1740.

Also, just to shed some light on required audio modifications to go along with the video. No circuitry is needed, just need to tap from the cartridge audio output directly from the 60pin connector. So that ends up being cartridge pin 46.

Here's some pictures of my install. My goal was minimal intrusion to the console. I favor a modification that can be easily reversed with minimal signs that anything had been touched. Making the console appear that it was designed with AV out was not my goal.. The idea of taking a knife to my famicom makes me cry..

Thinking about picking up some tiny coax to replace my ribbon cables and cheapo RCA connectors, was all I had on had and good enough for now!


Attachments:
File comment: Final result running on 1702, no clue why forum makes photo sideways... :? click on photo and it's right side up..
2017-04-20 21.36.23.jpg
2017-04-20 21.36.23.jpg [ 2.34 MiB | Viewed 1842 times ]
File comment: Jacks fed out the airy game/TV switch
2017-04-20 21.37.41.jpg
2017-04-20 21.37.41.jpg [ 1.45 MiB | Viewed 1842 times ]
File comment: wiring to main board for video and audio
2017-04-20 21.23.54.jpg
2017-04-20 21.23.54.jpg [ 1.77 MiB | Viewed 1842 times ]
File comment: twin famicom video circuit on perf board mounted in original RF module
2017-04-20 21.15.12.jpg
2017-04-20 21.15.12.jpg [ 1.57 MiB | Viewed 1842 times ]

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