Sega Mega Drive Genesis technical details

Sega Mega Drive Genesis

Back in 1999, I've got a Mega Drive for a present, Sony Playstation came out big, we used to rent it. No one near me had the money to buy it. Mega Drive is of course outdated. For me, who only had some Famiclone until that time, it was still good. I was trading some Xmen game for probably two of the worst games in human history. VR Troopers and Evander Hollyfield Boxing. Then my neighbor gave me Ristar in a box. I also bought the first two Sonic games. That 16-bit blast processing is slowly becoming one of my favorite consoles ever. 

Let's get technical! 

Mega Drive (メガフライブ), called Sega Genesis in North America and Super Gam*Boi (수퍼겠보이), later Super Aladdin Boy (수퍼알라니보) in South Korea. Codenamed Sega Mark V during development, it is Sega's fifth video game console (following the SG-1000, SG-1000 II, Sega Mark III, and Sega Master System). The Mega Drive's selling point was its 16-bit main processor, which, in addition to superior graphics capabilities, enabled a more advanced gaming experience previously only possible in arcade games. Full technical details can be found here:

Mega Drive Technical Details

It was also called baby neogeo, because it had the same processor, the Motorola 68000, but of course it was far weaker than the SNK Neogeo Mvs arcade machine and the home variant Aes.

What sets the console apart and why it is my favorite is that it has a specific FM synth sound. The YM2612 chip is what, in my opinion, separates the console from other 16-bit consoles, so to speak. Despite the limited palette of colors that it can display on the screen at the same time, compared to its contemporaries SNES/Super Famicom and PC Engine, which will be discussed in the following articles, it has that distorted synth sound, a special charm. Unlike SNES, for example. which sounds midi, like an orchestra, clean.

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Hardware revisions

Let's start with the hardest part.

In Japan, the PC Engine was sold big time and then took over the 16-bit Snes/Supa Famicom market, the Mega Drive went unnoticed. However, it was very popular in America and was a competitor with SNES. Europe, Brazil also had good sales.

High demand, especially from '95 in the poorer EMEA regions of Europe, such as Russia, parts of Asia and Eastern Europe, and Sega's desire to drain the last drop of blood in mega drive game sales, led to the Mega Drive being the absolute most cloned console possibly ever. A huge pain in the crotch area when it comes to hardware and the lack of quality control, you can see by the official number of revisions.

In general, the Mega Drive has officially had 3 iterations. Mega Drive 1, 2 and 3.

It would take 3 days to write the differences for each. Detailed differences in hardware revisions can be found at the following links.

Mega Drive Hardware Revisions - Sega Retro

Board Revisions

Which console should I buy?


The general rule is that Mega Drive 1 have better sound than Mega Drive 2. The sound through the din8 port is mono with the MD1 and even through rgb scart. Through the 3.5mm jack, there is crystal clear stereo sound. 

Mega Drive 1

The MD1 VA0 is the first Japan-only version. They say there are vertical lines on both the composite image and the RGB, I didn't notice it on the RGB. 

MD1 VA1 and VA2 are similar. 

VA4 is the first PAL European revision. Whichever of these first 4 revisions you take, you are not wrong. 

Starting with VA5, Sega introduces the TMSS TradeMark Security System, something like region lock/copy protection. You must have seen at the beginning of the bootloader this:

TradeMark Security System (TMSS) is a feature of Sega Mega Drive motherboards. It's the first thing that runs when you turn on the console, displaying a copyright notice.

Apart from some games requiring this as a check and additional checks to see if the system is 50Hz PAL or 60Hz NTSC, there is no difference.

In Europe, the most Mega Drive 1 consoles are VA6.5 and VA6.8. Both great consoles but have this TMSS.

With the MD1 VA7, in fact, the reduction in components and quality begins in order to save money. That is per se the same board as the Mega Drive 2 VA0. 

Mega Drive 2

A complete internal redesign with most of the main chips consolidated into a custom ASIC, increased use of surface mount chips and has one 7805 voltage regulator instead of two. Video quality has been improved over previous revisions. It has poor sound quality due to poor choice of components in the audio circuit. 

So MD2 VA0 as we said, is condensed MD1 VA7. Poor sound quality, but that's when compared to the MD1. MD2 VA1 and VA1.8 slightly improved sound. The rca/composite picture is slightly better by default than with the MD1. 

MD2 VA4 is the most preferred version of all Mega Drive 2, because it has the best composite picture and the best sound among all the two (most balanced). Kind of like the holy grail or 1chip of the Super Nintendo.

Mega Drive 3

Essentially a highly condensed VA4 model 2 without an expansion port. Although it is not compatible with the 32X or Master System games, it can be modified for these due to it using the same 315-5960 GOAC as the VA4 model 2. One other major change is that stereo sound was omitted, and all audio goes through a single LM324 op-amp. The Sony CXA1645 video encoder was also carried over, providing decent quality composite video output and RGB.

Generally Sony encoders tend to provide better composite out rather than Fujitsu or Samsung encoders. RGB is always (more or less) fine.

There are 2 revisions of MD3, VA1 and VA2.

More on video out and encoders:

Mega Drive Video Out

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Sound

The heart of the Mega Drive's sound hardware is the Yamaha YM2612 FM synthesizer chip, derived from the YM2203 chip that Sega used in a number of arcade games (eg Hang-On, Space Harrier, others). The YM2612 has six channels of 4-carrier FM synthesis, with a sixth channel capable of playing an 8-bit PCM sample. Unlike the YM2203 and YM2151 that Sega also used in arcade hardware, the YM2612 also has a built-in stereo DAC (digital-to-analog converter), saving motherboard space and manufacturing costs.

With the YM2612 are four PSG audio channels (three square waves and one noise) originating from the VDP. The PSG core used in the VDP is based on the TexasInstruments SN76489, which was first used in discrete form on the SG-1000 and then as an integrated core in the Master system. In many Mega Drive games, PSG is usually used for sound effects, but it has also been used to great effect in some games for main and background tunes. Two YouTube videos from the guy I follow where you can hear how powerful the Mega Drive audio chip actually is.  YT @RetroCore

Video 1

Video 2


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Modes and Clones

In order for your mega drive console not to sound like a broken audio cassette tape in 50 lines, not to mention hertz or frames. Mod it.

MD1 60Hz Mod

MD2 60hz mod

When your console shows a black and white image after that mod, use rgb scart. 

That is the best possible picture and then the quartz-crystal oscillator is not important anymore.

How to recognize a clone? Best see the pcb. Sometimes of course, it is not possible to see the pcb to know for sure.

None of the clones have SEGA written on the chips. 

MD2 clones have the SEGA logo in the middle (upper shell), the originals have it a little offset lower. The bottom side, under the Sega sticker, a short underline for clones, a long one for clones. Voltage is misspelled in clones. Also, original vonsoles miss the "dot" engraved on the bottom shell, where it says patent pending, the clones are followed by a "dot" after pending. And obvious things, when the board is slightly dark green, when there is no Sega CD port, etc. 

Russians are crazy gurus for mega drives. Here is a video where Russian explaining it how to recognize a clone. Well, in Russian. 😁

How to recognize a clone?

Newer clones, the Russians call them "novodeli", are mostly system on a chip, blob and mostly bad. However, there are also very good clones from the 90s, with MD1 as plates and MD2. Russians call them "starodeli". 

Another Russian video:  YT @alexmtechno_315

Some good clones