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S > SEGA > Genesis


Thanks to Sean Smith (Las Vegas - Nevada) for the following information :

I wanted to share some reasearch i have done on the american Sega Genesis, I believe this may apply to the Mega Drives as well.

There were quite a bit of revisions of models, The early model in 1989 could play unlicenced titles because it didn't have a lockout chip, and read High Definition Graphics on the top of the ring and had an external port on the back for a modem that was only released in japan. It also had better audio clarity.

Then in 1990 they added the lockout chip while still keeping the external port on the back and the High Definiton logo still on the top of the ring, this revision still has clear audio.

Then in 1992 Sega decided to take out the external port, remove the High Definition Graphics logo and make the red part of the plastic around the light a seperate piece of plastic, before it was painted on the ring. This models audio was fuzzy sounding and the contacs on the expansion port for the sega CD were not silver anymore; they put cheap black material for the contacs.

There is a model bettween 1990 and 1992 revisions that had the High Definition Graphics logo removed and the external port removed but inside the hardware is the same.

When 1992 came around they stoped using the big Motorolla processor and used a cheap set of clone chips.

That concludes all the revisions of the model 1 Genesis. The best one to get is the 1989 one. You get the full quality of what you would have payed for in 1989. There are distinctive factors that tell you the differance when shopping for one, first of all you will want to look for one with the "HIGH DEFINITION GRAPHICS" logo on the top of the ring or "High AV Terminal" for the japanese mega drive. Then to tell if it is the 1989 model with out the lockout chip instead of the 1990 model with it, you want to look at the front rubber boots on the botom that support the system. The 1989 model will have real rubber boots and the 1990 model and later will have plastic. Good luck and have fun, If you find one of these you have to get the Sega CD Model 1 for it, they also have better audio clarity and generally look better with the Model 1 Genesis.

Epicenter (USA) sends us some corrections concerning the text above :

Just wanted to correct some inaccuracies in the original post.

#1. The Megadrive never had a lockout chip. The glue chip had a new BIOS incorporated into it in a secondary revision adding the copy protection .. also the VDP Then required SEGA be written into it before it would start up.

#2. The MC68HC000 (smaller surface mount 68000) or Hitachi HD68HC000 weren't 'cheaper clones'. The MC68HC000 is a surface mount variant from Motorola. Hitachi's HD68HC000 is a licensed clone and actually performs MORE work per clock tick than the real McCoy from Motorola under numerous tests I've performed. The only weaker clone was the Signetics SCN68000 used in the VERY FIRST versions of the MegaDrive model 1, which did FAR LESS work per clock tick, about 20% less!

#3. I am unable to confirm claims of any lower sound quality on newer MegaDrive revisions except the Genesis 3 released by Majesco which omitted the Z80 and incorporated a workalike into a large combination chip.

#4. The EXT port acted as a controller port and is wired into the glue chip as such. It was used to select a game on a second display in the MegaTech/MegaPlay arcade system. It was removed from the design spec shortly after the first revisions at the same time as HIGH DEFINITION GRAPHICS was removed from the lid.

I may be wrong about this but I believe the modem released in Japan utilized the cartridge slot or Mega CD / Demo Unit edge connector rather than this port. However the Megaplay/Tech application appears to be the intended purpose of this port.

For all interested, the MegaDrive/Genesis overclocking page is here:

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