Genesis:Motherboard Differences

Some page content & researching taken from io55.net's Sega Genesis page with permission, in collaboration.

There were numerous models and variations of the Genesis/Mega Drive hardware produced over the years, ranging from standalone consoles to handhelds and even an unusual boombox/game console hybrid. This page serves to document these models and all variations (if any) found within each.

Models and Revisions

Models are arranged chronologically. Revisions are underneath their respective model.

Model 1 (1988-1992)

The model 1 Genesis/Mega Drive is easily distinguished from the model 2, as it is rectangular, with a large and raised circular area on top containing the cartridge slot, "16-Bit" text and the console logo in the case of the Genesis. Audio output is known as being vastly superior on most of these models, although stereo must be routed through the headphone jack instead of the usual AV port, which was inherited from the Master System. One downside is that most revisions have a minor "vertical bar" issue in the video output, while revisions with lessened vertical bars come with the TMSS lockout program. Earlier revisions of the Model 1 have an EXT port on the back, similar in pin structure to a 9-pin RS-232 serial port. One specific late revision of this model has horrible audio quality. Production largely stayed in Japan though most Western models were manufactured in Taiwan, China and Thailand.

"VA0" (1988)

This is the earliest revision of the model 1 and is only found in Japanese Mega Drive consoles. These are distinguished by a small daughterboard which contains the master oscillator crystal and a few support chips. Although the board is not designated as such, it is commonly referred to as the "VA0" in keeping with Sega's revision naming practices and the fact that it was the first board revision produced.

VA1 (1989)

VA2 (1989)

The primary element of this variant is the peculiar situation with the sound output. While the balance between frequencies is excellent, the preamp is far too high, resulting in horrible distortion in games that are too loud. Otherwise, this revision maintains the usual distinctions of the “HDG” Genesis consoles, such as clean and crisp video output, the EXT port, and the “FJ846EUSASEGA” FCC ID (this will be important later). Apparently, the preamp issue can be fixed with just a few changes to resistors.

VA3/VA4 (1990)

A usual circumstance for “High Definition Graphics” Model 1s remains, this being the clean and crisp video output, EXT port, and long FCC ID. Alongside this, the audio situation has been changed from the VA2, lowering the preamp, but somewhat altering the balance between frequencies. This results in no more distortion in loud games, but a slightly poorer frequency response curve, leading to a minor muffling.

VA5/VA6 (1991-1992)

Of the changes on this revision, the crucial difference is the inclusion of the “TMSS” lockout screen (Produced by or under license etc.) on the VA6 that appears for a bit before playing any game. These are MOSTLY identifiable by the FCC ID, which has been shortened to “FJ8USASEGA”, although some VA6es do NOT have this FCC ID. Furthermore, the video output is moderately improved, as the “jailbars” or “rainbow banding” issue has been fixed on these. Otherwise, all is identical to the VA3 and VA4 (EXT, great audio). The VA5 board is identical but has a different I/O chip which does not have TMSS. These boards are only found in Asian and Japanese Mega Drive models.

For the remaining model 1 revisions, the "High Definition Graphics" slogan at the top is removed. The "AV Intelligent Terminal" text on Asian/Japanese models was also removed at around the same time.

VA6.5 (1992)

These are easily identified by the aforementioned slogan removal, alongside viewing the ports at the back. The EXT port is no longer available on these consoles, but the other ports have not changed position compared to prior revisions. This presentation will result in the four remaining ports being justified to the right of the I/O area, leaving a reasonable gap to the left where the EXT port was. Outside of this change, this revision is identical to the HDG VA3-6 systems (TMSS/banding status is unknown). Some people claim they have a slogan-free Genesis that still has the EXT port, so if one finds such a console, it can be guaranteed to be of this revision.

It is worth noting that the EXT port was not removed for Japanese models as the Mega Modem attachment, which made use of this port, was still being actively supported.

VA6.8 (1992)

Only found in European Mega Drives, the VA6.8 revision is largely identical to the VA6 but has a surface-mount Fujitsu MB3514 video encoder in place of the DIP Sony CXA1145 found in most other models.

VA7 (1992)

Introduced in late 1992, the VA7 was the final and most drastic revision of the model 1 released. It is the first Genesis/Mega Drive to use the FC1004 ASIC found in most model 2 consoles, which combines the VDP, I/O and a YM3438 audio chip into a single chip. All VA7s use a surface-mount version of the Sony CXA1145 encoder as well as a QFP version of the Motorola 68000 CPU.

The ports on the back have been shifted significantly to the left, having the AV out occupy where the EXT port used to be (except on Japanese VA7s which still have the EXT port present), which leaves a large gap to the right. In addition, the sound output is notoriously bad when compared to other revisions; it is muffled, filled with hiss, and possesses a flat frequency range with excessive distortion. This is due to Sega using an inadequate amplifier circuit and can be corrected using a modification board such as the Triple Bypass or Mega Amp.

TeraDrive (1991)

Wondermega RG-M1 (1992)

Model 2 (1993-1998)

These models introduced a redesigned smaller case, removing the raised circular area and changing the console’s shape to a square. The headphone jack has been removed, although the A/V output now supports stereo. However, the EXT port is completely removed, and audio output on some revisions is noticeably worse compared to the model 1. The RF port and channel switch have also been removed on Western models, as all models now make use of an external RF modulator.

All model 2 revisions can be distinguished by viewing the motherboard through the cartridge slot. See the "Sega-16" guide linked below for details.

VA0/1/1.8 full-size motherboard (1993-1995)

These are for the most part, very similar to the VA7 model 1. The sound quality still suffers though is not as bad as the VA7, leaving only the incessant hissing. Alas, the lack of a volume slider (since the headphone jack was removed) eliminates any ability to change the volume of the hiss. At times, the video output may also be very poor if the console uses the Samsung KA2195D video encoder; this is something that can only be determined by opening the console.

The VA1 differs from the VA0 mainly in that it consolidates the two VRAM chips and two 68K RAM chips with one chip each - and there are major trace routing changes to accommodate this. However, there are also some resistor values changed in the audio circuit that likely reduce distortion in these later revisions: R42 through R45 are increased from 4.7 kohm to 7.5 kohm, while R81 is decreased from 7.5k to 6.8k.

It is unclear what exactly is different between the VA1 and VA1.8, as the boards appear mostly identical with the exact same components and no documentation of this difference has been found.

All three of these mainboard revisions come with or without HAL (Hot-Air Solder Leveling), although the "HAL" text is not always present on the boards which have it.

All three of these mainboard revisions also come with or without plated through-holes, and the layout is slightly different between these variations. The non-plated variations have extra vias. Additionally, the non-plated variations have jumper links in place of some power traces.

In Japan, the Mega Drive 2 only features either the VA0 or VA1 revision; later board revisions did not appear in Japan due to the Mega Drive's unpopularity there.

Model 2 VA0 Motherbaord

VA2/2.3 full-size motherboard (1994-1995)

Sound-wise, these are noticeably better than the 7/0/1/1.8 revisions, but it is still not perfect. Hissing is removed, but volume balancing, PSG sound, Master System, CD, and 32X sound are all faulty in some way. However, the likelihood of getting the bad Samsung video encoder chip is higher, although some of these will have a Sony CXA1645 instead, which is bright, sharp, and vivid. These are also the only revisions of the model 2 which have a discrete YM2612 like most model 1s, as the ASIC used in these revisions does not have a YM3438 core.

This board revision is only found in US Genesis consoles.

For the remaining Model 2 revisions, the motherboard’s size has been reduced by a quarter lengthwise. To determine the difference, look at the bottom of a model 2. If the metal plates visible through the exhaust vents end a significant distance from the edge of the console, it is a ¾ motherboard. If the metal plates practically touch the edge of the console, it is a full size.

VA3 ¾ motherboard (1994-1996)

These are about as hit and miss as the full-size motherboards. Identifying these can be done by looking for square cutouts on the metal plates (thru the vents). If the console has no square cutouts, it is of this revision. Depending on the encoder chip, video quality of these can range from utterly poor to acceptable. If this revision has a Sony CXA1645 or a Samsung KA2195D, the video output will likely be mediocre to horrible (although the Samsung isn’t the worst of the two). Luckily, sound is universally improved on all ¾ revisions, resulting in sound quality close to the first Model 1s (although with minor PSG difficulties). These will have compatibility issues with the MK-84000 model of the 32X.

VA4 ¾ motherboard (1996-1998)

Appears to be the best model 2 revision for output quality. All video issues have been eliminated, as the Sony CXA1645 chip in these is back to being crisp, colorful, and vivid. Furthermore, the sound has been improved a little more, eliminating further DAC noise than on the VA3. To identify one of these, look for two square cutouts on the metal plates (through the vents). These will also have compatibility issues with the MK-84000 model of the 32X.

Later VA4s in North America were sold under license by Majesco in 1998, who marketed the Genesis as a budget console. The build quality is largely identical to the earlier Sega-built examples. This was also the final board revision for the PAL Mega Drive II. PAL VA4 boards also feature a ROHM BH7236AF encoder, which is pin-compatible with the CXA1645.

Amstrad Mega PC (1993)

Wondermega RG-M2/X'Eye (1993-1994)

Mega Jet (1993-1994)

Perhaps one of the most novel versions of the Genesis/Mega Drive hardware, the Mega Jet is a semi-portable console initially made available in 1993 on certain Japan Air Lines flights and on March 10, 1994 to the general public in Japan only. It is essentially a Mega Drive 2 condensed into a handheld form with a built-in 6-button controller, although it lacks a built-in screen or the ability to accept batteries, basically making it akin to a "plug & play" controller with a cartridge slot. The Mega Jet's hardware would later form the basis for the truly portable Genesis Nomad.

CDX/Multi-Mega (1994)

A small console combining the Sega CD and Genesis/Mega Drive together, while also functioning as a portable CD player. Only some thousands of these were made, resulting in significant rarity. Video quality of these systems is quite good, but the sound is a bit mixed (too quiet, weak bass without headphones). FMV-heavy Sega CD games may freeze up on this system. It is compatible with the 32X and Power Base Converter despite its different physical form compared to standalone Genesis/Mega Drive consoles, and also features the same 9-pin mini-DIN video out as the model 2 with RGB output.

Aiwa Mega CD (1994)

Genesis Nomad (1995)

Genesis 3 (1998-1999)

Only released in North America. Less commonly seen than the prior two versions, this variant was actually released by a licensee, Majesco, instead of Sega themselves (who designed it). These are easily identified by their much smaller size, and of course the large “3” on the top. Many features have been removed, such as the headphone port, EXT port, expansion port (meaning no Sega CD compatibility, power LED, and even stereo sound. Furthermore, certain games such as Gargoyles have compatibility issues with these consoles (revision dependent) due to the removal of a memory addressing bug. Other games as well as the 32X and Power Base Converter are incompatible due to the cartridge port not being fully connected as with earlier consoles.

VA1 (1998)

Essentially a highly condensed VA4 model 2 without an expansion port. All compatibility issues (except Sega CD and TAS instruction issues) can be fixed on this variant. Virtua Racing will boot on this one, while it will stay at a black screen on the VA2. Without a copy of Virtua Racing, it can be hard to determine the revision; the cartridge slot must be opened, and the traces need to be inspected. It appears that the VA1 has a vertical trace on the far left, which cannot be found on the VA2. Lastly, the video output is known to be extremely high quality and still has RGB output. The sound is also high quality, although it is monophonic with a slight hiss.

VA2 (1998-1999)

Generally inferior to the VA1, as almost all of the compatibility issues cannot be fixed due to the VA2 using a different ASIC. In particular, 32X and Master System compatibility cannot be restored on this revision; only the Game Genie and Virtua Racing problems are fixable on the VA2. Video output quality was not changed, but the audio is a little better in low frequencies, and does not hiss.