Nintendo Famicom AV mod

The original Nintendo Famicom launched in Japan in 1983. At the time the best way to get video from the console to the TV was RF (and in Japan they used different RF frequencies to EU and US). This leaves people picking up a Famicom these days (especially those in the UK like myself) in a bit of an awkward spot – not only is RF a horrible way to get a picture on a modern TV, it also likely won’t work on a non-Japanese TV anyway.

There are quite a few mods floating round the internet which guide you through teasing your Famicom to output something a little more modern. The conclusion I drew pretty rapidly was that RGB output is out of the window unless you’re going to spend a lot of money, lower your expectations to composite and don’t expect a perfect picture. Given the age of the machine I’m pretty impressed that it still works, especially as mine appears to be a second revision motherboard – how many Playstation 3’s are still working that have a second revision board, I strongly suspect they won’t be after 30 years!

Anyway, on to the mod!

I chose to do this mod from “80sFREAK”, it seemed to be the best documented out there but I still found it pretty difficult to follow, partly because the Famicom board shown doesn’t match mine exactly – some of the PCB traces and components are positioned differently. Luckily there’s a few people out there who have also tried this mod which was enough for me to piece together where everything connects, of particular help was this blog post, this post and this other guide (particularly for labelling of pin numbers on the PPU) so thanks to both of the authors!

Important notes

• This mod disables the RF output
• You will need to shoe horn in two phono connectors somehow
• You will only get mono sound (which is all the Famicom and NES were capable of anyway)
• If you break it it’s your fault

Shopping list

• 100r Cr25 0.25w Cf Resistor

• 150r Cr25 0.25w Cf Resistor

• 33uf 16v 2.5mm Tantalum Bead Capacitor

• 220uf 10v 105deg Nrsz Electro Capacitor

• Yellow Phono Socket

• Red or Black Phono Socket

Modification

Step 1

Take apart the Famicom, there’s a good walkthrough on IFIXIT

Step 2

On the board there’s a transistor labelled ECB, carefully desolder it and keep it handy. It gets reused in this mod.

The transistor has a notch in it, use this to keep track of which pins are which when it has been removed.

Step 3

The original guide will tell you at this step to isolate pin 21 of the PPU (the Picture Processing Unit, the largest chip next to the ECB transistor). I tried this mod without isolating it and then went back and isolated it and saw very little difference, your mileage may vary.

If you want to do this step there are two recommended methods in the original tutorial, either lift the chip leg or cut the PCB trace. I cut the trace but, as mentioned earlier, my PCB differs from the one shown in the guide.

This picture shows pin 21 (red square) on the reverse of the PCB and shows the trace which I cut (orange line):

Step 4

Build the circuit shown in step 3 of the original guide, I’ve borrowed 80sFREAK’s images here (@80sFREAK – if this is a problem just contact me and i’ll remove them).

Though the advise is to keep wires as short as possible I chose to do this on a board as it separated it nicely from the PCB and left me with no fears of it shorting!

This is the numbering for the PPU legs on the component side of the board:

 Step 5

That’s the video output done, now to add audio. Follow the circuit diagram and solder to pin 46 of the cartridge connector (again these are 80sFREAK’s images)

For this one I soldered to the back of the PCB as the pins are much more accessible (and there’s enough wires now trailing off the front!)

Step 6

With everything wired up this is a good chance to stop and check whether it works before you go drilling holes in the case!

Assuming it’s all working pick somewhere on the case that your mod can reach and that’s convenient for AV connectors and make some holes! I personally went for the front right as there’s a fair amount of free space on either side at the front.

 Step 7

Cram it all into the case and screw it back together!

Hopefully it all works and you’ve got a reasonable quality picture, mine occasionally jumps a little and has pretty visible “jailbars” but overall it’s pretty good for a console from 1983.