USB NES mod - yeah, I know it's silly. ;)

This assumes you already know how to fully break down your system.

1) Remove "MOD RF" box. Best to desolder the 5 pins on the actual back of the RF modulator board instead of at the NES motherboard. This prevents traces getting lifted.
2) Bridge orange and red lines on power switch board.
3) Solder USB ground to where shield of the RF modulator was soldered to. Also check that voltage has not been reversed before step 4! Unplug USB from power.
4) Solder USB +5V to pin going to brown wire on power switch board's connector.
5) Before applying power, double check that the switch is turning the NES on and off, using an ohm meter. Do continuity/visual checks for solder bridges or wrong connections.
6) If no cart is in it, and the CIC chip hasn't been disabled, then when powered up, the LED should blink on and off. Finally a good use for that circuit! XD
7) Add replacement video amp to the video output. Nearest the cartidge port, among those 5 pins that used to go to the RF modulator, is the (needing amplification) video output from the PPU. This goes to the input of your replacement amp. The output goes to an RCA connector, and the ground and VCC lines should be obvious by now. (VCC/+5V is the middle pin of the old RF modulator's connector, ground is the shield)
8) Audio can be sent directly to your TV but you might want to add an amp and headphone connector, as well.

The USB plug should be going to charger and not to a PC directly. This is especially true if you're using a lot of controllers and a Flash cart! For similar reasons, don't use micro-USB sockets. A male end of a (full-sized) USB extension or a female type-B socket is recommended.


NESp notes about the big-honking-box: http://nesp.tighelory.com/construction/chapter_3/page1.shtml

An example of the replacement video amp (NES2, but similar): http://longhornengineer.com/2011/07/19/ ... schematic/
Cleaner schematic, skip the stereo mod nonsense: http://console5.com/wiki/Nintendo_NES-1 ... dification
And again for the NES2: http://www.gamesx.com/rgbadd/nes2avmod.htm

Schematic of the real video amp is here: http://www.neshq.com/hardgen/ (schem2) and here(much cleaner): http://console5.com/wiki/File:NES-001-S ... Switch.png

One I'm trying: http://nesp.tighelory.com/images/nesp_amplifier.gif

What is this mod for?
Is this a joke?

It could be useful for running an NES Control Deck off a newer car's USB charger port (or an older car's 12 V to USB adapter) and feeding the video to the monitors in the back of the front seats.

It's also useful if you don't want to use the enormous power brick that originally came with the console. I've seen plenty of USB AC adapters that can provide upwards of 1 amp at 5 volts, which ought to be plenty for a NES.

After some investigation, though, it turns out getting power out of USB is a lot more complicated than I thought. There's a surprising variety of official and proprietary standards for identifying when it's safe to draw more than 100mA from a USB port. (The good news is, most devices are smart enough to shut off if you draw too much current. The bad news is, there are a lot of knockoff Apple chargers that probably cut cost by removing the overload detection.)

I imagine that manufacturers have started to standardize on what the USB IF's Battery Charging spec calls a "dedicated charging port".

It's not (entirely) a joke, but it is still funny to plug a NES into a hub running off a PC when the easier way is to just get FCEUX. I had technical reasons to need a real NES, since the entire point of getting it was to help me test a custom cart.

This was because I hated the original RF/AV/power box and didn't want to bother getting a wall wart that is both inconvenient and inefficient. It also works on 4 rechargeable batteries, BTW...

I don't know why you'd hate the box, it isn't particularly bad at its job. You can get an efficient switching power supply and use it on your NES. The power section of the NES expects AC power and rectifies it inside, so it'll take just about everything you throw at it.

Also the NES will operate properly even if you *inject* 5V through the 2P controller port ... haha

No need to gut the RF modulator out or even open the console.

I guess it's only 3" of 28ga wire carying ≈half an amp, so it's not a significant voltage drop or resistive heating...

I've wanted to try this, but, isn't there a possibility of the noise from the switching power supply (USB charger) negatively impacting the image quality?

Very, very unlikely. The frequency would be too high.

What I noticed (I used a PC as power source) is that the NES collected all sort of power rail noises the USB devices connected to the PC generated. Including hovering the mouse around the mouse pad and keystrokes on the keyboard could be heard on the audio output.

But the video quality was the same as the usual.

How many mA does it draw when using a controller port power injector? I'm wondering if a controller extension cable with a built-in power regulator and injector (using the USB Battery Charging spec) might be a viable product.

Practically it will draw the exact amount it would draw from the original 7805 chip. (motherboard + cartridge + controllers). Because the NES has no fuse or any kind of short circuit protection on the controller port "injecting"power through it has no ill/negative effects.

A similar thing done on a SNES would leave you with the system working but no sound as the sound amplifiers do rely on the 10v from the power supply for power (they need 10-12v to operate the audio op amps).

And how much is that typically? USB from a PC or self-powered hub officially provides up to 500 mA after negotiation. USB from a Charging Downstream Port (after negotiation) or Dedicated Charging Port can provide more.

Plain NROM games have been around 350 mA, IME. The PowerPak is a lot more, but I don't know how much.

On that note, you can feed the amplifier 5V and everything will be just fine.

Most desktop PCs don't have control over the current supplied by the USB port. Putting the current control devices on the design are actually very expensive so they just put one of those low resistance self resettable PTC circuit breakers. So if the current exceeds the maximum current permitted by the PTC device the port stops supplying current until the PTC device cools off.

USB 2.0 ports are rated for 1 amp. USB 1.1 500ma.

Some devices actually implement the full design (particularly true for portable devices like laptops and tablets) as they're more critical with power stuff.

I'm very doubtful that it would be safe to power the output of the 7805, I don't know if any were designed to handle that. Plus I don't know if Nintendo used parts from different manufacturers, which might allow for different ways for it to screw up (AN7805, Matsushita? in the one next to me). I mean, that's no problem for playing around, but I certainly wouldn't build something that out-of-spec into a product.

I had a similar thought not too long ago about the NES expansion port. The unregulated, rectified voltage is there. But by the time you deal with that expansion port connector, and disconnect the 7805, you might as well just wire a damn module in place of the 7805, hehe.

I'm not totally sure I understand what situation you're describing - do you mean placing a voltage at the 7805's output? If you're referring to my post, I meant giving 5V in place of where the 7805's output pin used to be, not while it is present.

Many of the plain linear 7805s I've tested act like a shunt regulator at 5V... you'll statically lose some power into them by back-feeding them, but I wouldn't be worried about damaging them.

Sorry, I should have quoted a post, I was talking about injecting power into the controller port.

So, I'm still a newb at switching power supplies in practice, I wonder if the proper selection of switching frequency work well, as in, not have any audible effect. One solution it seems like people use if noise is a problem, is a switching regulator followed by a linear regulator. Though I guess that's not much help with USB 5V, you'd probably want 6V or something.

edit:


I just noticed my last couple sentences are suggesting that solution too.

edit 2: Except that I'm forgetting that the AN7805 isn't an LDO, 6V is too low. 7.5V minimum maybe?

They always recommend 3v higher than the target voltage, "at least".

Not to mention I also didn't account for voltage drop through the bridge rectifier.

Keep in mind that the NES is often okay with ~4.5 volts, which gives a little bit of helpful tolerance.