Retro Teardown: The Sega Genesis

December 15, 2016 by Robin Mitchell

In this Retro Teardown, we will open up the Sega Genesis (also known as the Mega Drive) to see how these were designed.

In this Retro Teardown, we will open up the Sega Genesis (also known as the Mega Drive) to see how these were designed.

The Genesis

In the beginning, there was nothing. Then, suddenly, the creator said “let there be 16 bits of color”. The creator saw the color and said that it was good. On the second day, the creator then said “let there be sound” and thus the Yamaha chip came into existence. The creator saw this and thought it was good. After a few months of thinking and development, the Sega Genesis was born.

The Sega Genesis (also known as the Mega Drive in Europe) was a home gaming console that was released in 1989 in Japan and North America and in 1990 in the UK. Despite being discontinued in 1997, the Genesis is still available for purchase by retailers in many different forms (including the 80-in-1 game packages). As of today, over 30 million units were sold with over 900 games available for the console. Many consoles, by default, have Sonic the Hedgehog built in to provide a game out-of-the-box which spawned an entire franchise and, later, a mascot for Sega.

In this Retro Teardown, we'll see what's inside this iconic console.

Before we dive into the Genesis, a quick note to the audience. This Genesis has been in storage for a very long time and so I apologize for any dust, cobwebs, spiders, etc. that have decided to move in. Not to worry, however, since I have done my best to evict any unwanted squatters (I have not seen a penny of rent from any of the creatures that lurk in my loft).

The Outside

The front of the Genesis shows the main two controller ports, a power button, an indicator LED, and volume control for external headphones. The sound for the Genesis, by default, comes through the connected TV (typically through an RF connection on channel 36).


The front of the Sega Genesis


The back of the Genesis has information regarding the power consumption, company, and serial number. The back also shows some vent ports that are needed for heat removal (most likely due to some linear regulator which was common back in the day).


The back of the Genesis


The serial number of the Genesis


The back of the Genesis shows the IO ports which include a power connector, an RF output, an AV output, and an EXT output.


The back ports


The front ports show a headphone jack and two controller ports while the controls that are available on the front include a volume level, a reset button, and the power slider.


The controller ports


The controls on the front of the console


Didn’t you know that the Genesis does HD graphics?!

The side of the Genesis has an edge card that is hidden by a cover. This edge connector is similar to the one on the top that holds the game cartridges. The difference is that the side connector is the male PCB part of an edge connector instead of a socket.


Side edge connector

Inside the Genesis

With the top cover off, we can see the large metal shield that most likely improves EM compatibility. In a gaming environment, it is more important that the console is unaffected by nearby electronics than the other way around. Imagine being in Labyrinth Zone in Sonic the Hedgehog 1 and the console froze!


The large metal shield that covers the whole PCB (except the edge connector)

Removing the shield reveals the true beauty of this circuit. The PCB consists of a mixture of through hole and surface mount parts, which is peculiar as using a mixture increases production costs. Judging by the quality of the build so far,  it appears that money-saving was not on the priority list. Nice one, Sega!


The PCB of the Genesis


While the Genesis, on the whole, has a lovely looking circuit, this section has much to be desired. The large amount of electrolytic capacitors near the CXA1034 IC suggest some form of audio amplification for use with the headphone jack.


All those caps all over the place. Urgh!

Processing in the Genesis

The Sega Genesis has two 32KB RAM chips giving the total RAM space of 64KB. The IC responsible is the HM65256BLSP-10 which hold 32KB each. The PCB allows for either the narrow or wide DIP version of the package which creates fewer headaches if certain parts become unavailable or if one part is cheap at a particular time.


RAM ICs: the HM65256BLSP-10 32KB

The Genesis has two processors: the 68000 (a 32-bit processor with an external 16-bit bus) and the Z80 (8-bit processor). The 68000 is the main processor in the system which is clocked at 7.61MHz while the Z80 handles audio and is clocked at 4MHz.


The 68000 processor


The Z80 processor along with the 8KB SRAM (shared)

The Sega 315-5364 IC is a bus arbiter that controls data path flows between memory and the processors on the Genesis.


The Sega 315-5364 bus arbiter


The Sega 315-5313A is the Video Processing Unit of the Genesis (essentially the graphics card). This is the chip that takes in instructions and data to produce the graphics that is shown on the connected display. Like the other Sega Genesis ICs, these are custom ASIC chips so the IC itself is a generic array of gates and functional units which are then connected together by defining the metal layers by the customer.


The VPU of the Genesis: Sega 315-5313A

The Genesis also uses another IC for video manipulation, the Sony CXA1145P. However, this IC does not produce video but instead helps to create all the needed H-sync and V-sync signals needed to get a video signal to produce video on a TV correctly.


The Sony CXA1145P video “post-processor”

The Iconic Sound

Everyone who used the Genesis remembers one thing in particular: the sound and music! All of this is thanks to the iconic sound chip in the Genesis, the YM2612.

This IC is an FM synthesizer that produces all sound effects and music tracks while the IC itself is controlled by the Z80. This use of a co-processor results in music and sound effects that are not affected by the core processor (the 68000). Therefore, during times of heavy data processing, music still plays and sound effects are left unaffected.


The YM2612

The "Funnies" of the Genesis

The Genesis uses two separate 7805 regulators instead of one large regulator. This is possible so long as the two regulators are not sharing the same 5V line. If two 5V lines are used (one for processing ICs and the other for IO controllers), then no one 7805 will overheat due to excessive current draw.


The two 7805 regulators


Another strange aspect of the Genesis is the use of many capacitors with components with names including "EM". This would suggest that the function of these is to improve EM compatibility and power line stability.


The many EM capacitors

Output Video Ports

The video port of the Genesis shows the use of an RF modulator, which was common in just about every device from that era. Interestingly, the RF modulator was needed because no TV has composite video input which is what video processors from this time generated. Eventually, TVs included a composite input which meant that the RF modulator could be removed and the video output could be directly connected to the TV.


The various video ports


Many people prefer Nintendo products while some prefer modern consoles such as the Xbox and others have inclinations towards PC gaming. But the Sega Genesis clearly embodies a time when games had to rely on gameplay rather than graphics and audio to create games that were both entertaining and captivating.

The Genesis also demonstrates how programmers, graphic designers, and musicians alike had to really pull together to produce exciting games with limited hardware. At the end of the day, the Genesis is a truly amazing console that has provided millions of hours of entertainment.


Next Retro Teardown: Commodore 1541 Floppy Drive vs DVD Drive