Famicom | AV Mod

Quick update, the resistors that I ordered (what seems to be a lifetime ago), finally turned up so I decided to work on my famicom again.

First off I tried using pin 21, not sure if it's the famicom board but there seems to be no difference between that and using VIDEO.

Secondly I used a 1000uf cap between 5v and the collector on the PNP, jailbars are almost non existent, you can only see them if you literally put your nose up to your TV screen, all that's left for me to do now is close it all up and play some famicom games : )

 

I believe is time for me to get a famicom and try this mod, i like the challenges. I've done my hybrid NES but having a fami around is not bad.

 

That seems a bit drastic - if I wanted to disable the existing video buffer I would just lift the base on Q1 and short it to the collector - it's been a while, but I'm pretty sure that the only place the video signal from pin 21 of the PPU goes is that transistor. It's also got the advantage that it's easy to reinstate if you ever want to back out the mod, which really can't be said for cutting pins or board traces.

 

Just in case people are wondering, something went wrong with my famicom, the gfx were all scrambled up, I thought that it might be the PPU or a cut trace but the console had pretty much had it I think : (

Shame as I was really enjoying the learning process, anyway I've spotted a great deal on an AV famicom so I'm excited about that, I will continue with a few smaller projects from now on I think..

 

Don't give up so soon picking up a AV famicom would mean you have nothing to loose working on the old one either way its not a bad thing having two famicoms

 

Finally i`ve found the best famicom av mod

http://www.youtube.com/watch?v=yYuj5gzqrpI check this out, i`ve done it it really works, perfect picture and sound, no jailbars, nothing, finally!!!!!!!!!!!!!
2 minute work and done... i`m very happy, already playing mario bros

 

This was my solution in the end:


Glad that you got your Famicom to work, I saw the video, looks great : )

 

But you have to have an RF switchbox connected in order for it work, doesn't that almost defeat the purpose of having an AV mod?

 

The RF connection in the video is only being used for grounding... Most convoluted "method" ever.

Also it certainly won't work on every TV since the points being tapped are only meant to drive the RF modulator (low amplitude, high impedance) so the signal actually arriving at the TV will be extremely small/out of spec. A proper A/V mod will deliver a reasonable signal level into 75 ohms (AV Famicom). A great AV mod will deliver a precise, filtered signal into 75 ohms, with 75 ohms back termination (requiring an op amp of sorts).

 

Since we are discussing Famicom AV mods, I thought I would just chime in and show my work on my AV Fami. I need to do a bit more work on it since the picture is really blurry (even through an xRGB Mini), on account of the fact that I followed this diagram:



But I only had 2N4403 transistors on hand, and used a 330 ohm resistor instead of 300 and 100 ohm resistor instead of 110. I also assumed that the negative leg of the 220uF cap goes towards video out, I hope that was correct. However, lifting pin 21 was a fantastic decision as it is all but jailbar free now

I did lift pin 21 and soldered a wire from the pin around to the bottom of the board and connected to the transistor. Here are the photos of my work (again, will be re-doing this).

In this photo I added a filter cap to the 7805 because why not, the wire going from the 5v rail on the 7805 (with 330 ohm resistor) is going to the transistor:



In this photo, I connected the transistor to ground, (lifted) pin 21 (wire coming from underside of the board) and connected to the 5v rail (330 ohm resistor) to the transistor and also to a wire with a 100ohm resistor (the additional wire from the ground point near the transistor will be explained momentarily):



In this photo, I connected to the wire with the 100 ohm resistor to the positive leg of a 200uF cap, and then connected the negative leg of the cap to a bit of shielded cable with the ground/shield of the cable going off to ground via the wire we saw in the second photo. I also added a filter cap to the 5v rail on the CPU.



Finally, in this photo we just see the RCA jacks wired up:



I hope this was not a thread hi-jack, it was not its intended purpose, and again, this is only temporary until I get the correct parts. I know it's a mess, and the heatshrink looks horrible.

 

The one thing I regret about av modding my famicom is the fact I used RCA jacks :,(