Jump to content

ITC - Sega Master System

ITC - Sega Master System

I bought this SMS with 2 controllers and bunch of games over a decade ago at a garage sale for about $100. Since then it has been a constant occupant in the main game console case where the systems I actually play are connected up and added to the AV system. 

This SMS was an early project of mine for mod work only a year or two after I got it. It has had quit a bit of work done/redone, removed, added etc during that time. But thought it might be fun to see the chaos that exists within the inside of the ITC SMS. This is an early '86 made unit that has only the built in Snail Maze game and uses leaf switches for the pause and reset.

It has the following work done to it over the years:-

- FM add on board (Provides FM music & sound for games that support it)

- Region switch added (Some games only provide FM when set to JPN region)

- Hand made circuit for handling remote pause function from player 1 controller

- S-video amp (designed for a Genesis) installed to provide s-video output

- RCA jacks were added (wired from the audio & composite output of the built in AV port)

- Capacitors replaced about 4 - 5 years ago

- Original voltage regulator removed and replaced with DC-DC switching regulator

- RGB active amp & breakout added in Jan. 2024 for cleaner RGB and composite output from second 9-pin AV mini din


As a result or consequence of all of these services/modifications over the years, the work quality varies and I like this fact as it shows a progression from my early days of doing this stuff for myself personally to more higher skills I've developed since that time. As the list above shows, I added a replacement active RGB amp setup to it on Jan. 9th, 2024 to provide improved RGB output as the original has bad jail bars that can only be corrected with a modification like this being added. Most tech will remove the original AV jack and install the replacement there, but I chose to remove the RF modulator instead and install the second AV out port there. This way the original AV can be used on the original circuit or the new AV used with the new. This not only allows both as a point of comparison, but allows both to be used at the same time since they are from different isolated circuits so I can use the composite output from the original or RGB and provide a nicer composite or RGB from the other to two displays at once. 

The RGB setup that I installed was NOT designed for the model 1 SMS and in fact is designed for the model 2 SMS. But I figured I could adapt it and was curious to see if I could get it to work. I did, but it required me to meter out the points to take my signals from that the board needs. It also required me to add additional resistors to the RGB inputs to the RGB amp board. Try a few different values but it seems that 740 Ohms is pretty much were it needs to be. Each RGB signal is sending a .7v peak to peak signal to the amp/encoder on the new PCB and that is right at the high end of where you want that to be. Without the resistors the image was overly bright with quite a few colors not being displayed as they were blending together due to over driving the RGB amp. Using higher value resistors results in the image looking a bit too dark in some colors.

The FM board has the ability to not only provide FM synthesis sound and music on games that support it, and that is more than a few surprisingly. But also allows for changing the console country region between US and JPN. This is needed as a few games only provide their FM audio sound when they detect running on a JPN region console. This also results in a few games having different difficulty in their games along with different startup and title screens. Several games will boot up the console showing a MARK III logo vs the SEGA logo as this model of the SMS was known as the Mark III in Japan. However, getting the region switching to work was a chore as the original install guides for the SMS refer to attaching the needed wire for region switching to a completely different pin on the console than what actually works on these earlier model 1 consoles. The guide will tell you to lift pin 19 or cut the trace to it from the Gate Array IC chip. However, this result in a NON working SMS if you do this. In reality, you have to lift or cut the traces to pin 23 on the gate array IC and then run a wire from that pin back to the IORQ# pad on the FM board. Once this is done, the console will then switch between US/JPN properly.

The hand made remote pause is designed to allow you to pause the games on the console from the controller vs having to press the PAUSE button on the console. This is handy because many games will use the pause as a 3rd function button to pull up stats or inventory etc. It can be a pain to have to keep the console nearby for easy access to the pause button. So I found a circuit years ago that requires modifying your controller with a 3rd button that you wire to both the Left & Right, or Up & Down contacts. Basically when you press this 3rd button, it will send an impossible controller combo to the system that you can exploit as a trigger for simple logic circuit you add in the console that will then initiate the command to the Pause in the console. This is normally done using a NOR IC logic that will take the two inputs pressed at the same time to create a True logic output that you feed to the pause switch in the console to initiate the pause. However, mine is more complicated because I didn't have any NOR chips on hand at the time and so I use an AND IC logic chip instead and by routing the signals to several logic gates in that IC, it eventually creates the same True output logic that I feed to the Pause switch. I've thought about redoing this circuit over the years, but it works and I kinda like to see some of my early hand done stuff remain in use in some of my consoles.

- JH:- Ivory Tower Collections


  • Album created by CrossBow
  • Updated
  • 8 images

0 Album Comments

There are no comments to display.

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Add a comment...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...