Some time last year I experimented with SuperFX carts, creating a StarFox 2 and then doing some overclocking.  There’s a lot of info about this on the web scattered all over the place.  The main info is on the Console Mods forums by Drakon, then there’s a load of info on Assemblergames and what’s probably the original guide on benheck by marshallh.

Unfortunately I wasn’t very well at the time, so didn’t keep proper notes on it all, from what I can remember, Stunt Race FX/Wildtrax works well by a straigh forward swap of the timing crystal with a 2 pin one and some capacitors (I’ll add some photos of this further down), (most?) other games need a bit more work which I’ll detail first.

Oh, and there’s arguments about whether the GSU-2 chip overclocks better than the GSU-1, but I think it’s been confirmed by Mottzilla that they just have access to different amounts of memory or something, so shouldn’t have to worry about it too much.

Using 4 pin Crystal Oscillator

Righto, here’s my cart (opened up with a 3.8mm gamebit), you can see the GSU chip and some chips, resistors, crystal etc that we’re working with.  Leg 70 of the GSU is the clock input (this is for a GSU-1 chip, for a GSU-2 chip it’s 75, although I can’t find my working out for this now!  I did trace it back from the chip that the existing crystal connects to).  You can easily trace it to a nearby resistor, which in turn connects to a hex inverter which is working with the existing crystal etc.

You can simply cut the trace somewhere, or remove the resistor.  I decided to add some solder to the resistor and then moving my soldering iron from one contact to the other quickly to heat both up and push the resistor off.

Once it’s removed, you can easily wire in the 4 pin crystal.  Check the spec for your crystal, you need to indentify power, ground and signal.  In my photo that’s Power – Red, Ground – Black and Signal - Yellow.  When you’re finished, you can stick the crystal to the inside of the cart casing quite easily.  For testing, you can just pop the bare board into your console, don’t forget that the chips face away from you when you plug it in.

What crystal should you use?  I’ve already linked to it above, but here is a copy of Drakons excellent info on the subject

Different games have different speeds that they can run at without crashing. Here’s my list so far:

• Starfox: 28.322 mhz is the fastest I got this game going at without it crashing
• Doom: Also 28.322 mhz
• Starfox 2: 33 mhz (33.333)

Using 2 pin Crystal

I’m pretty sure this only gets results on StuntRace FX/Wildtrax and Vortex?  Anyway, locate the 3 pin timing crystal thing (probably blue or white) and desolder it.

Insert your 2 pin crystal through the outer holes, solder it into place and add some solder to the empty middle hole.  I’ll double check, I’m sure I used the same 24.000 mhz crystal that marshallh used.

Now add the 18pf capacitors, one from each leg of the crystal to the middle point.

Other random stuff which I may revisit and elaborate on/clarify

Swapping SRAM

One donor cart I used for StarFox 2 didn’t have enough SRAM on it, so I swapped some over from a different game that I was messing with that didn’t need so much!  There were enough solder points for it, I just had to prep them and move one capacitor.

Desoldering Chips

The following photos show how I insert a needle inbetween the legs of a chip, I heat the leg up and then lever that leg up and away from the board.  With a bit of practice, it doesn’t take too long to remove a chip.

This chip is the Mask ROM for StarFox (to get the best results overclocking this game, it’s recommended to put it onto a board with a GSU-1 (or 2) chip.  You can use this method for the SRAM chips too.