Project Genesis - Modding

Now that the repairs and maintenance are complete, I can move onto the final, and most exciting, phase of Project Genesis - "modding." Here I'll modify the Genesis to actually make it better than when it was new. The mods I'm going to make are S-Video, composite, and stereo audio out the back.

Originally the Sega Genesis (Mega Drive) output RF and composite video. My plan is to add a second composite output (more on that later) plus S-Video output which is supposedly much better! This is nothing new, there are tons of people who've performed the S-Video mod and posted their results on the Internet. But all of those posts seem to lack important details. It's my hope to fill in all the missing pieces for anyone else who wants to perform this mod.

To create the S-Video output I need to tap pins 15 and 16 of the CXA1145. Note: not all versions of the Sega Genesis use the CXA1145, so check before you assume this will work. I want to add a second composite output to the back even though the Genesis comes with a composite output. The reason being is the built-in composite requires a proprietary video cable, whereas I'm going to use a standard RCA jack. Finally I plan to add a stereo output jack on the back by tapping the CXA1034P audio chip directly. The schematic for all this should look like this.


S-Video
There are two main S-Video mods I've found on the Internet, David Howland's and Jamma Nation. The Jamma Nation one is newer and uses a much simpler design, so that's the one I'm going to use. However both designs don't give you all the necessary info. I decided to wire up the design on a breadboard first, this allowed me to make changes to the circuit to get the best possible performance out of the mod. Below is a list of the questions about the original designs, and the answers I determined.

1. Some designs use an amplifier for both the luma and the chroma lines, some designs only use an amp on the luma signal. Is the amp on the chroma line optional? Answer: I tested the circuit both with and without an amp on the chroma - I can say the amp on the chroma line does nothing. There was no noticeable difference in the video output with the amp on the chroma line
   
2. Most of the designs call for an NTE85 transistor on the luma amp, but this transistor is no longer in production. What transistor can be used in it's place? Answer: I used a 2n3904 transistor (specifically the 2N3904FS-ND on Digikey) and it worked great.
   
3. Many people who've done this mod state that the capacitor on the chroma line must have the positive towards the CXA1145 chip. Others state that the negative must be towards the CXA1145. Well they both can't be right, so which is it? Answer: I tested the cap forwards and backwards, the polarity made no difference. Since the polarity made no difference, I also tested a bi-polar capacitor and that worked as well. Since polarity didn't matter, in the end I went with the bi-polar capacitor.
   
4. For the chroma line they say to use a 220uF capacitor, but they don't specify the voltage needed. What voltage capacitor should one use? Answer: Using my multimeter on the live circuit I tested the voltage across the capacitor. The voltage never exceeded 2.5 volts. So for this mod I would suggest 6.3, 10, or 16 volts. Anything higher is just a waste. I went with 10 volt in my design.
   
5. Both the chroma and the luma lines call for a resistor, but no one says what wattage resistor to use. Answer: Again I tested this with my multimeter. Both the volts and the current were very low. Even when you multiple them together to get wattage, it was extremely low. So using 1/8 watt resistors leaves enough of a margin. You could also use 1/4 watt if you wanted to.
   
6. The luma line calls for a 27 ohm resistor, and the chroma line calls for a 75 ohm resistor. Varying these resistors greatly effects the quality of the video signal. So are these values truly the optimal values? Answer: On my breadboard I replaced the resistors with trimmers so I could adjust the resistance while the circuit was live. This allowed me to test the values to "see" what looked the best. The people who originally came up with this design did a good job, both of their resistor values were very close. The values I came up with as "optimal" were both within 1 ohm of the original values. So in my final circuit I used the 27 and 75 ohms from the original design.
   

Composite

1. As with the S-Video mod, some claim the capacitor must have the positive facing the CXA1145 chip and others say the negative. So which is it? Answer: I tested the cap forwards and backwards, as before the polarity made no difference. I also tested a bi-polar capacitor which also worked. In the end I went with the bi-polar capacitor.
   
2. They say to use a 220uF capacitor for the compostive, but they don't specify the voltage needed. What voltage capacitor should one use? Answer: Using my multimeter on the live circuit I tested the voltage across the capacitor. The voltage never exceeded 2.2 volts. So for this mod I would suggest 6.3, 10, or 16 volts. I went with 10 volt in my design.
   
3. Again, the composite signal uses a resistor, but no one says what wattage resistor to use. Answer: As before the volts and current very very low. So using 1/8 watt resistors leaves enough of a margin. You could also use 1/4 watt if you wanted to.
   
4. The original design calls for a 75 ohm resistor, but is this the optimal value? Answer: Testing with a trimmer I felt like the best video came from a resistor of 72 ohms. In my final design I went with the original value of 75 ohms as it's the only value I had on hand.
   

Stereo Audio

1. By tapping the CXA1034P directly you bypass the headphone amp and should get a cleaner signal. But is this output too low for the TV, does it need additional amplification? Answer: Surprisingly the audio output directly from the CXA1034P was perfect line-out levels. I did not need any amplification before passing onto the TV.
   
2. Does the headphone slider effect the audio output levels in anyway? Answer: The headphone slider does not affect the audio levels in anyway. So tapping the CXA1034P directly is a great way to get clean stereo audio.
   

Here's the final circuit design I went with:


Here's what it looked like on the breadboard.


Now that I've breadboarded up the design and I'm happy with it, time to solder it all up and squeeze it into the Genesis case. I also need to mount the connectors on the back. Whereas most people drill holes behind the cartridge slot, I decided to use the existing holes on the back of the Genesis. The back of the Genesis had 5 openings; power, proprietary A/V connector, RF output, RF channel selector, and the "EXT" port (which from what I've read was only used for debugging by developers). My plan is to remove the RF unit and EXT port which opens up three holes into which I can mount the S-Video, composite, and audio.

The picture below shows the solder points to clean out in order to remove the RF unit (shown in red) and EXT port (in blue). Getting the RF unit out ended up being tricky. The three point in a row were easy, but the large grounding points are difficult to clear out the solder. I ended up having to use a product call ChipQuik to get the RF unit out. By comparison the EXT port was a snap to remove.


And here's a picture with the RF unit and EXT ports removed.


Now it's just time to solder up all the connections. Here's all the wires connected to the underside of the motherboard.


As you can see in this picture I soldered the capacitors and transistor inline, covering the connections with heat shrink.


And the completed view of the back of the Genesis. I ended up drilling a single hole for the audio jack. The EXT port ended up being too large for the connectors, so that opening went unused.



And finally, the results...

Here are pictures of the composite versus S-Video output. As you can see the S-Video is noticeable clearer. You'll also notice the composite pictures are darker. There wasn't a change in the lighting, nor post image-processing, the S-Video output is just brighter and more vivid.












This mod was a lot of fun, and the quality of the video output was more than I had expected. If you're into retro gaming on the Genesis and if you have soldering skills, you might want to consider this mod. In the end the Genesis cost me $1, and the parts cost about $10.

Project Genesis - Maintenance

Now that the Sega Genesis has been repaired, I can move onto the maintenance phase. Whereas the console does work, it's 22 years old. So I want to do some preventative maintenance with the hopes it will work for another 22 years.

The first step was to clean the Genesis real good. For this I completely disassembled it. I washed the plastic parts in warm soapy water. The circuit board got blown off with a few blasts from my air compressor. And the connectors on the back of the unit got cleaned using a cotton swab and rubbing alcohol.

Probably the biggest problem with these old consoles is a bad connection between the cartridge and the console. If the console doesn't work, chances are the contacts are dirty. Previously I discussed how the best way to clean these connectors is to use cotton swabs with vinegar and rubbing alcohol (separate passes - not mixed together). This is easy to do for cartridges, but doesn't work for the console as cotton swabs don't fit into the cartridge slot. What I find works the best is to take a thin ridged object like a credit card, cut a strip of paper towel to the thickness of the credit card, fold the paper towel over the credit card, and use this go in and out of the cartridge slot. First use some vinegar to remove the oxides on the metal. Then change the paper towel and do a second pass with rubbing alcohol. This should do a great job of cleaning the slot.


The next step is to ensure there are no cracked solder joints. The repeated stresses on the board over the years might crack solder joints. If the console has intermittent problems, if one or both controller ports don't work, etc. then it's very likely there are cracked solder joints. Even if you don't have problems, it can be a good idea to touch up the joints. To do this you'll need a soldering iron and a little bit of leaded solder (I don't recommend lead-free solder as it tends to crack over time and is harder to work with). The best is a temperature controlled soldering station, but you can get by with an el-cheapo Radio Shack iron. A smaller tip is very helpful. Lastly, buy smaller diameter solder. To touch up the solder joints you do the following for each point:

Place the hot iron on the joint to melt the existing solder. Technically that's all you need to do. But it can be a good idea to add just a little bit of new solder to each point to ensure the joint is even stronger. You don't need to do this for every solder point in the console. Pick the joints that are most likely to have physical stresses. Those include the controller ports on the front, the audio/video and power connectors on the back, as well as the row of pins for the cartridge connector.


There was one more step which I considered but ultimately decided against. I was going to replace the electrolytic capacitors (a.k.a. recap the Genesis), but in the end I decided against this. Capacitors are often times the first components on a circuit board to go bad, so replacing them can be a good idea. I decided against this for several reasons. First, using what's called an ESR meter I tested the existing capacitors and they tested good. And the second main reason is because it's a lot of work. This model Sega Genesis has over 30 capacitors which is a lot. The cost is cheap, the replacement caps cost about 40 cents each.

Check back next time for the final task - modding.

Project Genesis - Repair

The first step in Project Genesis is to try and repair it. After all, if I can't repair it what good would it do to perform maintenance or "mod" it? Right away I know I will need a new power cord as the power cord that came with the system was cut.


For testing purposes I can use my bench power supply. Before I even try and power it up, I opened the console and immediately found additional problems. There were two blown traces on the top of the circuit board, and two more on the bottom. The two on the bottom were right where the power comes into the motherboard, and the two on the top were near the on/off switch. Here's a picture of the damage on the bottom of the motherboard. It was hard to get a picture of the top side so there's no picture of that damage.


To repair the traces on the bottom side I decided to solder the power wires onto the first component after the break. As for the traces on the top side, it was easier to solder some jumper wires onto the underside of the board.



With so many problems related to the power, I suspect the previous owner tried to use the wrong power cord with the Genesis. Either the polarity was backwards and/or the voltage was too high. This cause several traces on the motherboard to blow. The big question is was anything else damaged on the board? With the traces repaired I was finally ready to test it so I would soon know. I connected up my bench power supply, put a cartridge in, and turned the system on. It worked on the first try! So the Genesis is alive. I can now order a replacement power supply and get ready for the next task, maintenance.

Project Genesis

No, I'm not making some obscure reference to Star Trek II / III. No, "Project Genesis" refers to the latest project on my workbench.


I recently purchased a Sega Genesis off eBay for a whopping 99 cents, and it included a controller plus Sonic 2. Why was it so cheap? Simple, because it was being sold as "broken." This is the perfect project for me. I can work on it, have fun tinkering with it, and in the end if I can't fix it or if I break it even further, no big loss. This project is purely for fun as I already have a working Sega CDX.

My plan on this project will be in three distinct phases; 1) repair, 2) maintenance, and 3) modding. The repair phase is obvious, I hope to repair it and return it to working order. In the maintenance phase I am going to clean it up and make it good to go for another 20+ years. And finally I plan to "mod" the Genesis by adding S-video output. Each of these phases will be documented here and I'll include lots of pictures along the way.

Before I get started, I should say there are tons of different Sega Genesis models out there (or Sega Mega Drive for those who live outside North America). There was the original model 1, the model 2, and also the model 3. Each version was smaller than the previous. This is a model 1 Sega Genesis. Also, within each model there are different revisions. Specifically mine is the "VA6" model.




Below you can follow along with the next posts in the series.

• Project Genesis - Repair
  
• Project Genesis - Maintenance
  
• Project Genesis - Modding
  

The return of cartridges?

What do the Atari 2600, Sega Genesis, and Nintendo 64 have in common? They are all cartridge-based video game systems. But there hasn't been a cartridge-based video game system since the N64, nowadays everything is disc-based (be it CD, DVD, or BluRay). Well I wouldn't be surprised if future video game systems return to cartridges.

I know, at first that sounds like a step backwards - but if you think about it such a step would actually make sense. First off, why did companies stop using cartridges in favor of discs in the first place? The answer is simple - cost. Back in the day the chips needed to make cartridges were very expensive whereas mass producing discs is dirt cheap. But discs have some real drawbacks.

1. They are slow to load. Whereas cartridges are near instantaneous, discs are slow to spin and read. Also, disc loading speeds cannot improve beyond their current state. To load faster the disc needs to be spun faster, but they are already spinning the discs at their maximum, to spin them any faster would shatter the discs.
   
2. Discs are more fragile than cartridges. Discs are easy to scratch or break.
   
3. Discs are relatively large in size. Discs are 12cm (approx 5") in diameter, which means the drive has to be at least that large, which also means the game console has to at least be larger than the drive. For example look at the Wii, the console is the size of a disc drive, so without the drive how much smaller could the console be?
   
4. Discs are limited in capacity. Already it's not uncommon for games to come on multiple discs. One of the original selling points to discs was their greater capacity, but their capacity hasn't progressed at the same rate as memory chips.
   
5. Discs are relatively easy to duplicate (pirate). Yes, all modem video game consoles employ counter measures to prevent pirating, but still it happens. There are ways to modify your console machine to play pirated discs. As long as game consoles use the same media as home computers, pirating will be prevalent.
   

I wouldn't be surprised if a video game console in the near future returns to cartridges. Think of those handy thumb drives (a.k.a. flash drives) you carry in your pocket. Compared to discs those are a lot smaller, more durable, faster access times, and can store more data. So why not store games on drives like that? The cost is still higher than discs, but the cost per gigabyte has come way down thanks to thumb drives, RAM, and SSDs. The industry is pumping out memory chips at unbelievable rates.

Of course, I think the primary distribution method for games in the future will be downloads off the Internet. But as a secondary media (for purchase in stores) I see cartridges as a better option that discs. I guess we'll just have to wait and see if video game manufactures agree with me.