Composite and audio mod on PAL NES "Toaster" - how to guide

I have spent many hours working this out.

The box of tricks you get on a PAL NES "toaster" console is a circuit board about 2" x 2" enclosed in a heavily secured shilding unit that takes some work to remove and separate from the main board, then open up and get to the board.

This box has the AC in (yes, AC in not DC), RF output, composite and mono audio output. The AC goes into components then into a 7805 (hence no need for the AC as it converts to DC for the 7805), and the 7805 although outputs negative, isn't present on the small board. Confusing!

Anyway, after various tests and trimming, etc, worked out what is needed for the video. The video line from the motherboard is too weak so needs amplification, which is why it moves to the transistor. The audio also passes through various circuits, although needs no amplification as you can take it straight off the NES motherboard fine.

I looked on the net for options, found a few but they were for the NTSC NES 2 unit, and frankly, doesn't work on this PAL NES unit, I tried it.

Not knowing a great deal about electronics (learning though slowly), no idea what the coil is or how to rate it, what I do know is the circuit does not work without it present.

The pic below is the board after removing all the shielding, the RF modulator parts, etc. The parts circled are the parts you need for this mod. Keep the 7805 too. A 7805 is easy to wire - the pin nearest the "7" is the 7.5v in, middle is negative, and the "5" pin is the 5v output.



Schematic I made



Pic to clarify - now I know what works, I can wire it up properly!

 

For the AC input you have an diode bridge rectifier circuit (the round part with 4 pins) and an huge electrolytic capacitor. That gives about 11v DC out of 9v AC which then is input on the 7805. Indeed all that is "bypassable" if you intend to mod the system in a way you no longer need the metalic box.

And WOW no A/V on a NES or Famicom makes me sad. :crying:

The coil on the video output is meant to block radio frequency which irradiates from the PPU chip and other digital circuits from the NES CPU board.

These could interfere with the RF modulator, then filtering them make the image a little bit cleaner.

 

Interesting, thanks.

I don't understand why Nintendo used 9v AC and not standard 7.5v-12v DC power supplies. This would also have saved various components in the console which would have helped reduce manufacture costs a bit.

The composite doesn't work without the coil - no screen image at all, so needed; even when the circuit is inches away from the console board, are the radio waves that strong? There is no shielding, as you see, and the entire RF and a/v daughter board is long disconnected so not relevant anymore. Thoughts?

 

How does that work? It should be 9v - forward voltage drop.

9v - diode drop should be JUST over 7v, which is the minimum for the regulator. Any higher than 7v is simply burned up, as is the case in linear regulators.

This is strange. I don't think there's significant interference, since most NES video circuits do not have a L, but that's what it's wired for. Series inductors block AC, but video should be AC-coupled...

 

After a quick search with Google I found an article which explains it:

http://knol.google.com/k/electronic-circuits-design-for-beginners-chapter-1#

At the topic "Full wave rectifier" and it explains how and why the voltage will be around 11.3v.

Of course after putting a load on the circuit, the voltage will lower to values closer to that what we expect. (around 9.5v-10v)

Well I can only agree with you at that. But then I just wanted to comment on Bacteria's comment regarding the "parts before the LM7805" and be instructive ... :thumbsup:

Maybe I forgot to mention that the voltage gets lower when the load is connected...

That video output was feeding an RF modulator which by it's nature is sensible to the radio frequency noise generated by the digital circuits on the NES. When you wind an inductor you set which range of frequencies it should allow by the number of spirals it has.

This one on the picture is meant to filter very high frequencies (way above the ones existing on the video signal) and after your comment, I realized that I forgot to comment to Bacteria that he can omit the inductor as it was only needed by the original NES RF modulator.

If it was just a standard A/V out I agree with you that an inductor there would be waste of components. :thumbsup:

Bacteria: Why you don't try to clone the AV Famicom circuitry ?

 

I think AC adapters are rated in RMS, so RMS in, RMS out. Or does rectification force Vpeak? I had never thought about that.

I guess it could LPF oscillator noise/harmonics, but really everything else falls within the channel bandwidth.

The video output just needs a voltage follower amp, almost anything will do.

 

The NES is rated 1.3 amps, although it probably doesn't use that amount. The 7805 can cope up to about 1.5 amps as I recall. If Nintendo had used a 7.5v DC adaptor rated at 2 amps or more, it would have removed the need for the extra parts in the daughter board as this voltage feeds directly into the 7805 anyway (that is how i'm working the NES board act the moment, so know it works fine). One thing you don't get as "standard" running a NES like this is the reset and on/off buttons don't work, although mega easy to wire them up so they did. If they provided DC not AC as manufacturers, then it would have been a bit cheaper. Nevermind!

On my system, the RF circuitry on the daughter board is completely removed - in fact the whole board is removed, just the transistor, coil and resistor remain. If the coil is removed the video doesn't work, i've tried it. Can't see how the RF can cause any issues, there are no RF circuits now as the daughter board is removed - there were quite a few capacitors and other components on the daughter board for the RF adoption before.

 

The NES itself generates RF interference from that 21mhz oscillator (Isn't that 26Mhz-ish for PAL systems ?). And you can be sure that there's plenty of harmonics in it. Hence the metal cages.

Poor choice of parts, bad design/engineering and an endless supply of fail is why famiclones usually have sucky AV outputs. :lol:

 

The NES probably draws under 600mA. Famicoms under 500mA.

The reason for the rectifier in the console is so that 1) people couldn't fry their NES like people do all the time on Famicoms and 2) it removes rectification and filtering inside the power adapter, making it cheaper and easier for the consumer to replace should it get lost.

If there is noise, it's not induced electromagnetically, it's in the actual video signal. Video on a NES is generated at 21.48 MHz, if harmonics at 43 and 63 MHz got into the signal, once amplified it could affect the modulation at the channel frequency.

Instead of your circuit, I would remove the resistor and inductor, and replace them with a 33 ohm and 220 ohm resistor in series to GND. The video out is tapped between them.

 

Turns out the coil on the composite line is not needed - secured the circuit to the console board, tested without and with the coil - no difference, so there is no need for the coil!

 

The coil should only be needed for RF-modulation.

 

What is the ratings on the capacitors?

 

I am confused by why you need to try and take the composite and audio from a PAL NES when every PAL NES I have come across (UK, Italian, Greek(!) and German) has two AV ports on the side of the unit... maybe I am missing something here..

 

Hey, I did a mod like this one recently, but on PAL RGB NES.
Some pictures here : http://www.obsolete-tears.com/forum/viewtopic.php?f=8&t=6130
Some auto-translation with Google : http://translate.google.com/translate?u=http%3A%2F%2Fwww.obsolete-tears.com%2Fforum%2Fviewtopic.php%3Ff%3D8%26t%3D6130

Anyway I did a test with one of my NES. I fed it directly on the 7805 input with 9 V DC / 500 mA and it was working fine. It was working too with 6 V DC / 500 mA, but I got some discreet vertical lines on the black flat tint in Mario 3 intro.

My next NES modification is to remove all the AC rectifier part and replace the LM7805 (read that more than half of the energy is lost in heat with it) by a LM2676 which is far more efficient.

 

I did a mod today:


It is pretty easy. I only shielded the +5V and the video to make sure that they didnt interfer with each other. However this mod works way better with the Yobo Fc than it did with the nes. Im not 100% sure but i think it helped a little on the nes.

 

I forgot to say that for the mod on the PAL RGB NES, there's is a 510 Ohm resistor to replace by a 47 Ohm one. I guess it's why your composite video signal is to weak.

I have just checked on my PAL NES (the european version with RCA) and this resistor is here too. Maybe you have it on your model. If yes, maybe you can try this :
- Replace 510 Ohm resistor by 47 Ohm one.
- Put a second 47 Ohm resistor between composite out of the motherboard and your RCA connector.

 

Interesting - my video looked nice, perhaps a different variant?

 

Just read again the original post. You have the european version, so it's the same as the one we have in France, except for the daughter board which you have removed.
So what I said before should work and you won't need transistor to amplify the video signal.

But as Jamtex said, why are you doing all this ?

If I remember well, the LM7805 datasheet says that the input voltage should be at least 3 V over the output, that's why input voltage requirement starts at 8 V.
If you're doing this for a portable, I suggest you to replace the 7805 by something more efficient like LM2676.

 

Interesting -lower ohm resistor and no need for the transistor - I wonder why it's there in the first place?

 

I don't know, maybe they wanted a common base for the console with a video signal which could be easily modified by different daugther boards according to the destination country.