SEGA CD Multibios
Before you do a single thing, read this tutorial from top to bottom, twice, and make sure you understood everything.
You will need a soldering iron with 15-25 W and a pen tip. Soldering guns are NOT suitable. A bit of wire (ribbon cable helps avoiding a mess, i.e. use an old IDE cable). Also, two switches, ON-ON, single pole (3 pins, 2 positions, included).
Some solder as well of course. Solder grease for tinning the wires and improving contact will be helpful, but isn't necessary. Most of all, you will need good light and a steady hand. If you are loosing concentration or feel you need a break, then take the break! Rather take a bit longer than mess up.
I will assume that you are capable of opening up the system and remove the shielding plates, all it takes is removing the screws. I also assume you know which end of the soldering iron gets hot, and how to handle desoldering equipment.
The eprom you received will look like this:
There is only a single chip in the system that has the same size and pin number. That's the BIOS. In the model 1, it's on the right side, in the model 2, it's below the Genesis connector.
On a model 1 SegaCD, it is easy to access the BIOS. Solder all 40 pins into place, and make sure there are no shorts. The old BIOS will stay in place, but will be disabled. This is done because the BIOS in model 1 is soldered on both sides (top and bottom), making it difficult and dangerous to remove. On a model 2 SegaCD, the BIOS is positioned below the Genesis connector and harder to reach. You have 2 possibilities to install the new BIOS:
a) You desolder the bios with either professional desoldering equipment (desoldering braid will NOT suffice, you WILL take off traces that way when pulling out the eprom), or (which I do now) use a Dremel with cutoff wheel to carefully cut the pins accessible (I usually cut them down till they almost break, then do the rest with scissors.. lowers the risk of slipping. If you hit the pcb, it's fucked, so be very careful and use a low speed). Cut them as close to the old chip as possible. Then bend the BIOS eprom slowly upwards and back down, repeat it until the pins break off on the other side as well. DON'T bend it sideways or rip it off!
Now, using small pliers and your soldering iron, heat up the pins from above and pull them carefully out. Don't heat them up too long. After this is done, clean the holes from solder with a desoldering pump (recommended) or braid, and put the socket into place. Remember to bend up and wire pins 38+39 before you put it in. You might also want to put a little tape below them so they won't touch the pcb.
It's a brute force method, but quick, and in fact the most stable and sturdy connection. I modded 3 systems that way now, and they all work very well.
Don't attempt this if you do not have a steady hand and good control over a Dremel tool!
or..
b) You only solder the pins accessible to you, and press the other side firmly against the old BIOS (the socket/eprom should sit snug on top of the original BIOS, all pins touching the old BIOS' pins without being bent). Solder at least the corner pins on the inner side (pin 21 and 40) by touching the solder and iron to it till some solder attaches them. There's just enough space to reach the outter pins on either side. If that side of the socket can't be lifted easily anymore, then you got good contact. I'll take some pics of that ASAP.
Alternatively, you could attempt to solder the other side too by using good flashlight and a small soldering iron, as well as a steady hand (alot harder, but highly recommended over the single-sided soldering).
If the SegaCD only shows a black screen after powerup, try pulling the BIOS slightly against the original eprom. Soldering the corner pins should ensure enough contact, tho.. it worked fine for me.
I recommend using a Model 1 for this MOD, it's much easier and safer to do. Model 1's can be grabbed on ebay regulary for less than 50$.
The sockets I use and sell with my MultiBIOS will fit on top of the original BIOS smoothly.
I'm too lazy to re-do all pics with a socket. I have decided to sell the MultiBIOS complete with socket, so do all the below modifications on the socket, not the eprom. The eprom will just be pushed into the socket when all is done.
First, you will have to lift pins 20, 38 and 39 so they stick out straight from the chip. Do not bend them too far and don't wiggle them, or they might break off!
Now you have to disconnect pin 20 of the original BIOS. This is done by either heating up the solder from the bottom of the PCB and pushing the pin up with a small screwdriver (make sure you don't scratch the PCB), or by cutting it as close to the PCB as possible with very small pliers or sharp scissors (those bent ones for cutting fingernails are very good for this). Lift the remains of the pin to stick out sideways as well, and ensure there is no contact to the PCB anymore.
Then, connect the necessary wires to the pins as shown in this schematic:
- Pin 39 connects to the middle pin on switch 1, pin 38 to the middle pin on switch 2.
- Pin 1 connects to the left pins of both switches (link them with a wire)
- Pin 30 (or 11, whichever is more convenient for you) connects to the right pins of the switches.
- Pin 1 also connects to the lifted pin 20 of the old BIOS (only if you are soldering on top of the old BIOS)
- The lifted Pin 20 of the new BIOS connects to the hole on the PCB in which pin 20 of the old BIOS used to be in.
Make sure the cables are connected firmly and won't come off easily:
Pin 20 on both eproms should be in parallel, like this:
(Disregard the 3rd wire at the top, only the bottom 2 count)
Finally, place the new eprom on top of the old BIOS eprom, and push the pins against it a bit so they will make good contact.
Also make sure the small hole on one side points into the same direction on BOTH chips.
Now, with a steady hand, solder the new BIOS into place. The best way is to hold a bit of solder against the pins where they touch, and heat it up for a moment so a bit of solder melts to the pins. Make sure you have good contact, but also ensure you don't use too much solder, or it might get messy. Shake off the solder from the soldering iron onto a piece of paper every 4-5 pins, so the solder won't collect and starts sticking several pins together.
If you accidentally melt 2 pins together, use a desoldering pump or desoldering braid to remove the solder before continuing.
On a model 2, cover the visible pins with a bit of electric tape now, so the shielding plate will not make contact.
After double- and triple checking all connections, put the system together as basic as possible (i.e. no screws, but make sure there are no shorts and all cables are plugged in), and test it. If all works as it should (that being, powers up and shows a different BIOS screen in the 3 switch positions), take it apart again. If you don't get anything at all, first check the connection of the Genesis to the SegaCD. If the power light comes on, but you get a black screen, re-check all connections.
Alternatively, you could solder an eprom socket (included and highly recommended!) on top of the old BIOS. The advantage of this would be that you can plug in and remove the BIOS eprom, don't have to bend the pins on the eprom (but rather on a cheap socket) and also have a bit more space to solder. Just do all of the above with the socket instead, and plug in the eprom when you are done. It might look like a tight fit, but the old BIOS with a socket on top and the eprom plugged in will fit exactly under the shielding plate in the model 1 and the metal piece below the connector in the model 2..
It should look something like this now:
Model 1
Model 2
As the final step, you have to install the switches in the case.
Choose a spot in the case where the switches will not touch anything else, after shielding and case parts are put back into place. On a model 1, the left side is suitable, on a model 2 the bottom right side in front of the drive will work well, or before the drive lid, left and right of the plastic pole, next to the drive light.I recommend using an electric drill with a 6 mm wood drill. If you don't have one, burning a hole with the soldering iron will work, but make sure you don't breathe in the smoke, and clean the tip immediately afterwards. Cut or break off all remains of molten plastic around the hole.
Stick the switches through and tighten the screws so they will not move around.
Put everything back together (don't forget the shielding plates), make sure no wires are in the way, and if everything went well, sit down and enjoy!
For anyone who just shit their pants reading this:
It's not as hard as it might seem at first. All solder spots are fairly large, the only difficulty might be getting the corner pins soldered on a model 2. If you are unsure, print out this tutorial and ask a local electronics shop to do it for you for a fee, or ask a friend who's good with a soldering iron.
Additional Information:
When using a PAL game on a NTSC genesis, or a NTSC game on a PAL MegaDrive, you might experience desync with the sound, most noticable in movie sequences (i.e. in Lunar). The only way to fix that is by installing a 50/60 Hz switch in your genesis, or using the correct version for your country (i.e. US Lunar on US Genny or PAL Lunar on PAL MegaDrive). For switch installation instructions, check SegaXtreme (http://www.segaxtreme.com/).
I also added a (very basic) BIOS switch template that you can stick onto your genesis with tape to remember the switch positions. Just edit it in netscape or notepad to match your switches (combinations vary, depending on which way your switches are installed)
And finally, the disclaimer:
I take no responsibility if you mess this modification up. I guarantee that the eprom and its contents are working, but I can not and will not guarantee that you are able to perform the mod. Again, if in doubt, ask a professional or more skilled person to do it.
If you have any questions, email me and I will answer them as well as possible.
This BIOS is in no way licensed by SEGA.
The BIOS files used are copyrighted and owned by SEGA.
Thanks to:
- Eidolon for his information and help
- Ex-Cyber for removing the country check in the BIOS
- LordC for sending me the PAL model 1 to dump the BIOS
- Flavio for the switching info (whereever he may be)
and everyone who keeps the SegaCD alive.
This document was written 2001 by Arakon.
