S-Video Modification

Many people have grown (rightfully) weary of their system's composite video output (see the Arcade Works section for reasons why) and have sought a way to view the Sega Genesis in improved S-video.  Fortunately, S-video is possible for all model 1 and most model 2 Genesis systems by simply amplifying the Chroma and Luma lines from the CXA1145 or MB3514 circuit.  Here is the schematic I made for it:




Note that the signal input capacitors are sometimes necessary to remove for the best quality signal. 

CDX RGB/Video Repair

Some CDX systems need to have their RGB lines amplified to output a correct signal to your monitor.  I spent some time tracing out the signals and devising a fix for my unit:

This is where the RGB signals originate from, just a point of reference should you want to test if your processor is outputting video at all.  The sync output is on the opposite side of this chip and can be traced from the chroma encoder.


Here are the main points of interest- this is where the RGB is most usable (after going through 4.7k resistors) because the initial signal is a little too strong to be worked with.  Wire opamps to these points like so:


This is an EL5410 quad op amp from Intersil.  I actually gutted this from a broken PSOne screen but it can also be found on their site for a very inexpensive price.  This is a terrific opamp for this mod and produces amazing RGB output.  Here is the opamp function for the RGB fix:



Now onto the video fix:

These 0.1uf caps shave worn out with the CDX's age and cause considerable video noise in all formats.  The RGB lines feed through these caps before they go onto the MB3514 chroma encoder.  Replace this caps with new 0.1uf ones for huge improvement in video quality.
Note that your chroma encoder should be a MB3514 and not the BH7236AF shown above.  This is an improved chroma encoder that I swapped in for the MB3514.





   Genesis 3 Stereo and Import Modification

The 3rd revision of the Sega Genesis console is definitely a space saver around the house but for some odd reason Majesco/Sega left Stereo sound out.  This is a VA2 Genesis 3 board but the idea is the same for modding other Genesis 3's:


First off, the import mod is very easy to do here and is exactly the same as the majority of Genesis versions out there.  The main CPU has 2 "detect" lines for region settings.  When both are connected to logic high (+5v) you get 60hz US.  When both are connected to logic low (GND) you get 50hz JP.  Just use 2 SPDT switches to swap between settings.

Now onto the stereo mod- 
The main CPU outputs 3 different audio channels that are combined together before going to the LM324 opamp and then onto the output jack.  The 3 channels are labeled above as left, right, and sound effects.  By disconnecting the one resistor shown above you get Left audio output at line level.  To get a correct audio right output you need to amplify the audio right channel to line level.  I did so by using another LM324 quad opamp.  If the sound isn't perfectly balanced you can use pots to adjust the levels to your liking.  Here is my finished Genesis 3 modification with my Component video board connected via an RGB jack I installed.  I also added a blue power LED:





Radica S-Video Mod

For those of you outside the modding scene, there was a new Genesis version released back around 2 years ago.  It is the Genesis Plug and Play system by Radica, a new Genesis sucked down to a single chip and the smallest version of the system to date.  Myself and some others at the Ben Heck forums figured out a way to attach a Genesis cartridge slot to the unit, making it a full Genesis console.  Since then I have done little work with the unit having been pre-occupied with arcade mods.  The one main drawback to this great little system is its lack of decent video output- so far the system has supported nothing but composite (crappy) video.  I noticed that there were 2 video signals that the GOAC (Genesis-on-a-chip) emitted and immediately suspected S-video compatibility.  I finally got around to pulling S-video from the system.  Here is my first schematic for doing it:


Right click to see full size

While this schematic is missing some details it will give you a general idea on how to perform the mod.  The Radica sends out both Y and C signals via the obvious choke inductors on the PCB.  From here the signals are mixed and thrown into a general purpose NPN for amplification.  The trick is to separate the signals before this amp and to build/supply another amp for the second video line.  The easiest way to do this (which I did to come up with this mod) is to simply have another Radica board on hand.  Power the both boards and split all the signals but use the amp and parts on the second board for the Chroma line.  Pull the amped Chroma signal directly from the NPN like in the schematic and voila, improved Radica video.  I apologize for not having the capacitance values yet but they are SMD so they cannot be read on hand.  I need to invest in a new multimeter to read them.  Here are the comparison pics:


Composite is on the left and S-video is on the right.  The blur in the composite image is not from my camera at all but simply the downgraded video quality.  Notice how the colors are improved and the image is sharper.  I was hoping for an even larger difference in image quality but I suppose the video lines coming GOAC are not the greatest quality (possibly due to a crappy video encoder within the chip?)  In any case I am still pleased with having a way to improve the image quality

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