Genesis:Genesis Model Differences

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

There are 4 models of the Genesis. Of these models, the Model 1 has 5 revisions, the Model 2 has 4 revisions, the III has 2 revisions, and the CDX has none.

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

“Genesis (Model 1)” (1989-1992?)
The Model 1 is easily distinguished from the Model 2, as it is rectangular, with a large and raised circular area on top containing the cartridge slot and logo. Audio output is known as being vastly superior on these models, although stereo must be routed through the headphone jack instead of the usual AV port. One downside is that most revisions have a minor "vertical bars" 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 usual RS-232 serial port. One specific late revision of this model has horrible audio quality. Model MK-1601 was made in Japan, while the rest were made in Taiwan. Certain versions of the Sega CD require plastic spacers to work correctly on this model.

“VA2 motherboard; High Definition Graphics at top” (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.

“VA3-5 motherboard; High Definition Graphics at top” (1989-1990?/91?)
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.

“VA6 motherboard; TMSS; High Definition Graphics at top” (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.) 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 VA3-5s (EXT, great audio).

''For the remaining Model 1 revisions, the High Definition Graphics slogan at the top is removed. Thus, it will not be mentioned in the names of both following revisions.''

“VA6/6.5/6.8 motherboard” (1992?)
These are easily identified by the aforementioned slogan removal, alongside viewing the ports at the back. EXT is no longer available on these consoles, but the other ports have not changed position, compared to the prior revisions. This presentation will result in the 4 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.

“VA7 motherboard” (1992)
Only two visible changes are known within this revision, but the impacts are drastic. Firstly, the ports on the back have been shifted significantly to the left, having a port occupy where EXT used to be, which leaves a large gap to the right. Secondly, the sound output is notoriously bad when compared to other revisions. The audio is filled with hiss, with a flat frequency range, excess distortion, and somehow it’s also muffled. There is even a chance for poor video output, depending on the chip within.

“Genesis (Model 2)” (1993-1997?)
These models introduced a different case design, 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 removed, and audio output is noticeably worse compared to the Model 1. The RF port + channel switch have also been removed. Certain versions of the 32X and CD require special plates to work correctly on this model.

''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” (1993-1994?)
These are for the most part, very similar to the VA7 Model 1. The sound still sucks, although some chips offer improvements to the sound, leaving only the incessant hissing. Alas, the lack of a volume slider (headphone jack 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 replaces 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 the later revisions: R42 through R45 are increased from 4.7 kiloohm to 7.5 kiloohm, while R81 is decreased from 7.5k to 6.8k.

It's unclear what exactly is different between the VA1 and VA1.8, as the boards appear mostly identical 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.



“VA2/2.3 full size motherboard” (1994?)
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.

''For the remaining Model 2 revisions, the motherboard’s size has been reduced by 1/4th. 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 (thru the vents). These will also have compatibility issues with the MK-84000 model of the 32X.

“CDX” (1994?)
A model combining the Sega CD and Sega Genesis 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. Details about feature set (such as the presence of an RF out) are not researched.

“Genesis 3 (Majesco)” (1998-1999)
Less commonly seen than the prior two versions, this variant was actually released by an understudy, Majesco, in place of a first party release. These are easily identified by the much smaller size, and of course the large “3” on the top. Many features have been removed, such as the headphone port, the EXT port, the normal expansion port (Sega CD etc.), the power LED, and even stereo sound. Furthermore, certain games, notably Virtua Racing, have compatibility issues with these consoles (revision dependent), due to the removal of a memory addressing bug.

“VA1 motherboard” (1998?)
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. The sound is also high quality, although it is monophonic with a slight hiss.

“VA2 motherboard” (1999?)
Generally inferior to the VA1 III, as almost all of the compatibility issues cannot be fixed. Of the fixable issues, only the Game Genie and Virtua Racing problems are fixable. Video output quality is not changed, but the audio is a little better in low frequencies, and does not hiss.