This page is about converting a retail Jaguar CD to a developer Jaguar CD. This is done by replacing the BIOS ROM chip of the Jaguar CD by a Flash ROM that contains the developer version of the Jaguar CD BIOS.


Why would you need a developer Jaguar CD BIOS?

Good question. Till now only Jaguar CD software developers needed a developer BIOS. This because normal Jaguar CD players can only play Jaguar CDs that are encrypted by Atari thus preventing unlicensed developers from releasing Jaguar software. Using a developer Jaguar CD BIOS you can boot unencrypted CDs so that developers could test their program before they send the program to Atari for encryption.

With the demise of Atari it is no longer possible to encrypt CDs since the keys to encrypt Jaguar CDs has been lost. So current (homebrew) software developers can only create and release unencrypted CDs which need special hardware like a developer Jaguar CD or CD bypass cart to run. When you do this modification you can run unencrypted Jaguar CDs such as prototype CDs like "Caves of Fear", "American Hero", "Black Ice, White Noise" and upcoming homebrew CD games.


Why opening and soldering in my Jaguar CD if I can buy a CD bypass cart?

Another good question. At the time of writing there are three CD bypass options:

The first reason is the costs. The CD bypass solutions are quite expensive or hard to get (BattleSphere), although the games are worth their price alone. If you are already the proud owner of the old BattleSphere and the old Protector versions, then you might not want to buy the upgraded versions. But the standalone bypass cart is still quite expensive. Modifying your Jaguar CD with a developer BIOS will cost you less than $7 (largely depending on chip cost) and a lot of patience.

A second reason is that a modified Jaguar CD is much faster at booting a CD than a bypass cart. With a bypass cart, first the cart is booted and then the CD is booted making the startup time before actually loading the CD about twice as long.

A third reason is that you with a modified Jaguar CD still can use the cartridge slot for for example the MemoryTrack. Some unencrypted games like "America Hero" are able to use the MemoryTrack although most homebrew software probably won't support a MemoryTrack.



Modifying your Jaguar CD is not easy. To do this you need a lot of soldering experience and a lot of patience. Reassembling your Jaguar CD can be quite tricky too (e.g. problems with closing the lit). Do this modification at your own risk and don't blame me if something goes wrong.



The Jaguar developer bios only works in conjunction with a Jaguar with a Stubulator 1994 BIOS (green screen). So you first have to add the Stubulator BIOS to your Jaguar console. This can be done in the same way as adding the 'BJL' ROM as described on the web page of Matthias Domin. The disadvantage of this is that you can only have one additional boot ROM in your Jaguar so you can't have BJL anymore. Therefore I used, instead of 27C010 (128KB) EPROM, a 29F040 (512KB) Flash ROM and an additional rotary switch. With this I can switch between 5 boot ROM versions (the original version + 4 versions in the flash chip). A short description of this modification can be found here.

Before you begin make sure you have the following parts:


Step-by-step guide

Click on the pictures for a larger version.


First you have to disassemble your Jaguar CD. Begin by removing the 7 screws at the bottom of your player and remove the top part. Now you can remove the 4 screws on the printed circuit board (2 at the front and two in the cartridge connector). Then remove the PCB from the casing and disconnect the connector of the CD lit detection switch. Finally remove the two small bolts that hold the shielding to the PCB. If you don't have a torq screwdriver you can also use a normal screwdriver of the right size to unscrew the torq scews.
The Jaguar CD printed circuit board


Since there is no space to solder an socket with additional Flash ROM chip on top of the original ROM (piggy back) you have to remove the old BIOS ROM chip. I didn't want to solder the Flash directly on the original ROM because then you can't reprogram it anymore. The ROM chip is the large 32 pin chip below the cartridge connector.
You have to remove the 32 pin chip with the sticker

If you have a mini blowtorch or a hot air solder iron you can try to remove the old chip without destroying it. If you have only a solder iron it might be easier to just cut the legs of the chip with a knife or small cutter.


No way back now. Here I've cut all the legs on one side of the chip. Cutting the legs of the other side is easy now.
Half way removing the old BIOS ROM chip


When the chip is removed you need to clear the holes. Use a pair of tweezers to remove the leftover parts of the chip pins and use a solder sucker to clear the holes from solder.
The old BIOS chip is now completely removed


Now you can insert a 32 pin IC socket in place of the old BIOS chip.
Jaguar CD with IC socket for the BIOS ROM

If you don't need to have a switchable BIOS you can now program a 27C2001 or 27C020 (256KB) EPROM with the developer BIOS and insert it in the socket and reassemble your CD. But if you do that you can use your CD only with a Stubulated Jaguar.

Update: Glenn Bruner? has made a cracked CD-BIOS that can load unencrypted CD's but still works with a Jaguar with retail BIOS. You can program this BIOS in 27C020 instead without the need for a Stubulated Jaguar.

For a switchable BIOS read on.


Program the Flash chip with in the lower 256KB the developer BIOS and in the upper 256KB the regular BIOS. Insert the 29F040 Flash ROM in the socket except for pin 31. Pin 31 on the socket is A18 (unused) but on the Flash chip it is "write enable". To ensure correct working we must connect pin 31 of the Flash chip to VCC (pin 32)
Jaguar CD with the 29F040 Flash ROM

The easiest way is to solder a wire from the right contact of C72 (the contact connected to pin 32 of the IC socket) to pin 31 on the flash chip. In the picture it is the brown wire. I used a small socket to attach it to pin 31 so I can easily remove the connection.
It is not a good idea to directly solder the wire to the flash chip. My experience is that the Flash chip could loose its contents.


Now we need to make the BIOS switchable. We do this by toggling pin 1 (A18) of the Flash ROM between VCC and ground. Normally pin 1 is connected to VCC so we need to cut the trace between pin 1 and pin 32 on the underside of the PCB. On the picture it is the thick trace with TP250 written on it.
Cut the trace between pin 1 and 32

Next solder some wires on pin 1 (A18), pin 16 (ground) and pin 32 (VCC). On the picture respectively the brown, orange and orange wire.


Connect the wires to a toggle switch. Pin 1 of the BIOS ROM goes to the middle/common contact of the switch. Pin 16 and 32 go to the outer contacts of the switch. Now A18 can be toggled between VCC and ground thus selecting one of the two 256KB banks to use of the Flash ROM.

Be sure that the wires are long enough to reach the front of the Jaguar CD.
To keep the shielding up I used some sticky tape.


Drill a hole in the front of the bottom half of the Jaguar CD casing for the toggle switch.

Be sure that the switch is placed high enough so that the CD can still be placed on top of the Jaguar. If you place the switch too low, the switch will touch the Jaguar's housing and the CD may not fit on top of the Jaguar anymore.

The switch at the front of the Jaguar CD

Reassemble your Jaguar CD. First refit the torq screws of the shielding. Do not attach them too tight because then the non-conducting layer of the shielding can be damaged resulting in a short circuit with the PCB.

Next reconnect the connector of the CD lit switch and place the PCB back in the casing. Then insert the 4 screws of the PCB. Now comes the difficult part of putting both halves of the casing together. Be careful that the wires do not get stuck between the two halves. Also be sure that the CD lit switch is properly inserted in the hole of the upper part.

Finally screw both halves together.
The upgrade is completed


Connect your Jaguar and Jaguar CD and insert an unencrypted Jaguar CD. Set the switch of the CD so that the CD uses the developer BIOS. Set your Jaguar so that it uses the Stubulator BIOS. Now turn on Jaguar while holding the 'C' button of the joypad. If everything goes as intended the unencrypted CD will be run.
The Jaguar boots unencrypted CDs

If you turn on the Jaguar and the screen becomes red, than you have probably set the CD to the developer BIOS but the Jaguar is set to the retail BIOS.

If your Jaguar boots correctly but instead of booting the CD, it plays the CD in VLM, then the CD is probably set on the retail BIOS instead of the developer BIOS.