This guide was originally written by the people over at epicgaming.net, they no longer seem to be around so I’m hosting it and updating it. If you are someone from epicgameing.net and are upset with this; email me. I take no responseability if you fuck up your Nintendo.
Nintendo NES Model 1 Overclocking Guide
- This guide is for the Front-Loading NES model only.
- Not all machines are the same. Some NES units may not be able to be overclocked at all (though this should be extremely rare), some may go extremely far past their rating. These results are not indicative of any sort of guaranteed performance.
- Know how to solder. If you haven’t done it before, practice on some old dead circuitry before you get to work on your NES. You’ll be glad you did!
- You can destroy your NES. thejobbitt.com and its staff cannot be held responsible for any damages you may incur. Information here is used at your own risk! Don’t let me discourage you, though. This is a pretty easy modification to perform.
Step #1: Opening the Machine
Turn your NES Upside down and remove the six phillips screws recessed into the holes. Once removed, turn the unit back over and gently lift off the lid. Remove the RF shielding which is held in place with seven phillips screws. Once finished, remove the cartridge loader assembly (black device with springs). Don’t get the screws mixed up, there are two with a different length. Remove the two screws holding the power I/O unit down. Detach the power/reset, the player one, and player two connectors; this should have freed the board from the case. Once finished, you will want to familiarize yourself with the internals of the NES.
The NES is simply 2 small boards. One is the mainboard, the other is a small PCB that holds the power/reset switches and Power LED. On the mainboard are the CPU, PPU, RAM, Sound hardware, Ports, Connectors, the works.
Step #2: Cutting the Clock Trace
This is the most crucial and tricky part of the process so take your time here. Double-check, triple-check, quadruple-check. You need to cut off the original clock to the CPU before you can add your own. The clock is carried by a flat wire on the board called a trace. They’re the light-green wires you can see against the dark green mainboard surface.
Locate this rather large and obvious chip, labelled “RP2A03G”. This is the CPU, the “brain” of the NES. Pin 29, indicated in the above image, is where the CPU takes in its clock. So, the trace to that pin is what must be cut off. This is best done with a sharp implement like an x-acto knife or razor blade. You must be ABSOLUTELY CERTAIN TO ONLY CUT THE TRACE TO PIN 29. NO OTHERS! Note the giant mess I made of the board in the above photo; try not to do that. Cut into it slowly, then keep trying to boot the machine. Once it fails to boot, that should be your cue that you cut it deeply enough. Don’t overdo it though and come through to the back of the board!
Step #3: Testing the Clock Feed
Now would be a good time to make sure your machine is still functional and that you got the right trace. Turn the board over and find Pin 29 on the CPU, from the back this time. All the pins come through, as you can see. Solder a THIN wire to this pin, cut it to no longer than a foot, preferably under 8 inches. Now, you will want to hook the other end up to the clock source. Let’s try the original clock first, which can be found in a number of places. I find the PPU to be the best place to get this signal.
Find pin 18 on the PPU (labelled RP2C02G-0 or similar) as shown in the image above. I’ve chosen to attach a clip to it, as this is a temporary attachment just to test. If you’re careful you can also hold or tape the wire to the pin. Plug in a cartridge and try to boot the machine. If it works, you’re all set, go to the next step! If not, you may have cut the wrong trace, but due to common NES behavior, also make sure the cart is not dirty, your connector isn’t damaged, et cetera.
Step #4: Attaching a New Signal
Now it’s time to attach your new clock! Here you have a few options for clock generators, but your best bet for a quick cheap selection of new clocks are oscillators. They look like the image below (here’s also a pinout):
.. and have their clock output rating printed on them. Here’s the weird part. The CPU divides the clock you give it by 12 times to get the clock it truly runs at. So, if you wanted a clock speed of 2.0 MHz, you would connect an oscillator rated at 24 MHz. For 3.0 MHz, 36 MHz, etc. These oscillators need to be connected to +5 Volts DC, or +5VDC, a ground, and the CPU’s clock pin (pin 29) in this fashion:
+5VDC can be found at a number of places on the board. The obvious place would be the source, where all the power comes from– the voltage regulator. This part breaks down the 9VDC input into 5VDC. You can attach the wire from Pin 4 on your oscillator to this point, the OUTPUT (O) pin on the regulator. DO NOT, UNDER ANY CIRCUMSTANCES, LET THIS WIRE SLIP AND CONNECT TO OTHER PINS OF THE REGULATOR. IT WILL MOST LIKELY DESTROY THE REGULATOR AND PROBABLY YOUR ENTIRE MACHINE !! Erhem. Once this is done, attach Pin 2 to a ground on the machine, such as any of the metal borders of the mainboard or similar. Then connect Pin 3 to the CPU’s clock pin (29) using the shortest and thinnest lead you can.
Once your oscillator is fully wired up, boot the machine and see where you stand. Did it boot up? If so, congratulations, you’re now the proud owner of an overclocked NES!
I have found that a 3.0 MHz clock is to fast, both the NES’s that I have wouldn’t boot with a 36 MHz OSC. I recommend going with something smaller like a 25 MHz, 26.6 MHz or maybe a 32 MHz OSC. You can find them at Electronic Goldmine. Electronic Goldmine has a $10.00 min order so if you want one OSC and don’t want to spend $10.00 email me and I might have some extra; nick at thejobbitt dot com. If you do end up ordering from them get a switch and maybe a LED or something.
What’s that? You want to be able to change between the orginal and the new clock? That’s simple enough.
Optional Step #5: Making a Clock Switch
To pull this off you’ll need a simple ON-ON 2 position switch. This switch has 3 pins- 1 common terminal usually in the middle, and 2 others on either side. The center / common pin here should connect to the CPU’s clock pin (29). Then the 2 others should be wired to the clocks you’d like to use. For example, one to the PPU’s Pin 18 for the original clock (resulting in 1.79 MHz) and the other to your oscillator’s 3rd pin. Here is a diagram roughly detailing how this should be wired up.
Having trouble? Send me a email and maybe I can help.