techno-junk.org

I've added a big chunk of all the various technical documentation back online. There's more to come soon.

If you have any requests or feel what's available is out of date, let me know. Some files could older versions.

 

The Sega Master System has almost everything needed for RGB video output but is missing a few capacitors and resistors. I've designed a PCB that plugs into the A/V port that adds these missing components so you can get RGB video output without having to modify your console.

RGB adapter for SMS/SMS II.

There's a pass-through DIN connector for using an existing A/V cable to get monaural audio and composite video output. The DE-9 connector has a pinout compatible with Sony GVM monitors but the PCB layout could be modified for any other connector that is needed. There are jumpers to route the A/V input directly to the GVM connector, bypassing the extra components so it functions as a wiring converter only, and there's a pin header for monitoring signals on an oscilloscope or logic analyzer. I'll upload the design files for this project shortly.

 

The VA1 mainboard for the Sega Master System II has a footprint for a DIN connector underneath the RF modulator at location CN5. Adding this connector allows you to use A/V cables intended for the SMS or Genesis (original model). If you remove the modulator and short some unpopulated jumpers together you can route the A/V signals to the DIN connector to make it functional. The jumpers used are highlighted in red:

Jumper locations on VA1 mainboard (Click for larger).

The Sega Master System II service manual specifies that a ferrite bead (Taiyo Yuden FBA04VA600VB-00, 60Ω impedance) should be used for each JPx and FBxx jumper. Instead I used a small piece of green wire as shown in the image above. Short the following jumpers:

• JPR : Maps red video to DIN connector
• JPG : Maps green video to DIN connector
• JPB : Maps blue video to DIN connector
• JPS : Maps composite sync to DIN connector
• FB55 : Maps PSG audio to DIN connector
• FB56 : Maps +5V to DIN connector
• FB57 : Maps ground to DIN connector

The only missing signal is composite video which you can tap from pin 2 of the RF modulator connector. The VA1 board has two of these connectors to support different sized modulators so either one can be used.

 

I recently picked a PCB for an unknown Sega gambling game. It's the first one I've seen that directly drives a RGB monitor with the 315-5246 VDP without multiplexing the video output with other sources. As such, it makes a good example of a reference design for getting RGB output from that chip. Here's a schematic showing one color channel and the composite sync buffer:

315-5246 monitor interface schematic (Click for larger).

The VDP analog video output is AC coupled to the rest of the circuit to remove the VDP DC bias. The voltage divider and diode provide a new 1.9V DC bias for the video signal. The transistor is used in a common collector configuration to provide a a low impedance output capable sourcing enough current to drive a 75Ω load. It's a similar configuration to what's used in the Mega Play board but greatly simplified.

 

I'm updating the website so please don't report dead links for the time being. All the old content will be restored in the upcoming weeks.