How to run Gauntlet and Gauntlet II on the same board

The following text was written by Jay 'Whip' Grizzard, with support from Eric Crabill and edited by me.

If you're like most folks who like Gauntlet, you like both Gauntlet I and Gauntlet II -- admit it, they've both got their good points and bad points. Also, if you're like most people, you don't have two Gauntlet cabinets lying around (I used to!--Eric) in your dorm/apartment/house or whatever. And finally, if you're like most people, you probably don't want to have to do an entire board swap (or ROM swap) just to switch between the two.

Well, now there is (still) a way to play both Gauntlet and Gauntlet II using the same board, with a single switch-flip toggling between the two. This also works to play Gauntlet 2 Player and Gauntlet II except you need two more 27512 EPROMS for sockets 9A & 9B

Disclaimer: This hack is NOT intended to allow for easy pirating of Gauntlet or Gauntlet II software -- please don't use it as such. Also, we take NO responsibility for any damage you do to your Gauntlet board (or anything else) while attempting this hack. Though the chances of actually damaging something are fairly small, they are there, so make sure you know what you're doing before you start hacking!

The theory: Gauntlet I and Gauntlet II use absolutely identical hardware. The only differences are some of the ROMs used, and the slapstic copy protection chip. If the ROMs were replaced with double-sized ROMs, with the highest address line wired to a switch, flipping that line between 5v and GND would, essentially, give two completely different ROM images. Other than the copy protection, this gives two completely functional games on one board.

We'll assume a few things in this documentation. First off, we'll assume that you're at least semi-technically competent. Second, we'll assume you have Gauntlet I and Gauntlet II ROM images. Third, we'll assume you have access to an EPROM burner.

First, get your parts together. You will need:
         4 27256 EPROMs (300ns or better)
         7 27512 EPROMs (300ns or better)
         1 2816 EEPPROM
         Various machined sockets (2 to 3 for each chip)  (optional)
         Lots of wire (awg 30 is good)
         A switch
         If you don't start with Gauntlet II you will need more EPROMs

Step 1: Get your ROMs ready.

The first thing you want to do is get your ROMs ready. Some of the ROMs, we won't be changing -- in particular, the ROMs in locations 9A & B, 6A & B, 1B, 2B, 1C, 2C, 1L, 2L, 1M/N, and 2M/N will remain the same as they were in Gauntlet II, so don't do anything with those. (We're keeping 9A & B, 1B, 2B, 1M/N, and 2M/N because they're the same in Gauntlet and Gauntlet II. We're keeping the rest because they're ONLY in Gauntlet II, and Gauntlet doesn't mind them being around). If you are starting from a Gauntlet board (not Gauntlet II) then you will need to add the appropriate Gauntlet II 6A, 6B, 1C, 2C, 1P, and 2P ROMs.

The chips we will be replacing are those in 13A/B, 10 A & B, 7 A & B, 1A, 2A, 1L, 2L, 6P, 16 R & S. The new images for all of these (other than 13A/B, which is the EEPROM that stores scores and settings) can be created fairly simply. The EEPROM doesn't need to be initialized.

For all the chips other than 10A, simply read in your original Gauntlet I and II ROMs, and burn new ones, into double sized chips, with the Gauntlet I ROM on the low half and the Gauntlet II ROM on the top half. For 16kbyte images (27128), the double-sized ROM to burn is the 27256, and for 32kbyte images, the double-sized ROM to burn is the 27512. If you are working with files, an easy way to merge two ROM images is to use the MS-DOS copy command, like this:

copy /b some_gaunt1.rom + matching_gaunt2.rom new_merged.rom

For the 10A ROMs download the two files at the end of this page. Burn the G1 file low, the G2 file high

Step 2: Install the ROMs.

Once you have your images, you need to wire up a way to switch the high address line on these chips between 5v and GND. You may choose your own method (it could be as simple as simply bending up a pin on the EPROMs and soldering wires or using a single IC socket pin, like I did), but here's what we personally recommend: Build a stack of 3 (or 2) sockets -- use -MACHINED- (not leaf) sockets. On the bottom two of the stack, remove the socket pin corresponding to the chip pin for the highest address line on that chip. On the topmost socket, solder (or wrap) a wire, and daisy-chain that wire from socket to socket, in essence shorting the high address lines of all the special EPROMs together.

I personally used wire-wrapping, building the sockets one at a time, working from the sound ROMs (up in the corner with the power connector) down around to the left, finishing with the ROM in the middle. Order doesn't matter, really. In retrospect, I probably would have started with the ROMs at 10A, then worked around to the alpha ROM (in the middle) and finished with the sound ROMs.

You probably want to check your sockets with a meter before you install them -- Obviously, the high address pin from each chip should be connected to the wired up pin on all the other sockets, and NO OTHER PINS.

Which pins? Well, on 27256's, the high address line (A14) is on pin 27. On 27512's, the high address line (A15) is on pin 1. On the 2816, you actually want to connect to pin 22. [For the un-initiated, IC pins are numbered, starting at 1, counter-clockwise from the notch on the chip.]

For reference, the 2816 is in location 13A/B, the 512's are in locations 16S, 7A & B, 1A, 2A, 1L and 2L. The 256's are in locations 16R, 10A & B, and 6P.

Once that's done, you'll have an almost-functional machine. Remember how we mentioned copy protection above? Well, the copy protection for both games is -different-, so we've had to work around it by altering parts of the ROMs. However, this work around also requires just a touch of hardware support -- you need to replace your slapstic, the chip in location 10C. Grab a 20-pin machined socket, and solder a wire between pins 4 and 10, then between pins 5 and 9, and plug this into where the slapstic used to be.

Now, if all is well, you'll have a switcharoo game. If the high address lines are grounded, you'll get Gauntlet, if they're at 5v, you'll get Gauntlet II. I, you could used those quick-plug style female connectors, plugged into the two test points (5v and GND) up next to where the player joysticks plug in (Note: some boards don't have a +5 test point). I used I single pole double throw switch (3 wires) as shown on the schematic, It's OK to flip the switch with the power on. It will crash the program and causes a wacthdog timer reboot.

Be sure to check out the Gauntlet Pause Switch page, too. Good Luck.

I own a set of both Gauntlet and Gauntlet II ROMs, so I need


Schematic of Game select switch (and other circuits)

Only the "Dual Game Select" section is needed for this mod. Even the LEDs and resistors are optional. See my other pages for information on the other sections.