SG-1000:SG-1000 Model Differences
The SG-1000 hardware only saw two major revisions, with one board revision for one of them.
Models
Original SG-1000 (1983-1984)
The original SG-1000 was released in Japan on July 15, 1983. It is easily distinguished by its large aluminum nameplate, red pause button and hardwired SJ-200 joystick. The top of the console is made of cream-colored plastic with a separate gray/beige piece which surrounds the cartridge port. At the rear of the console are the RF out, channel select, power input, and a 24-pin card edge connector which is the expansion port; this port was later used for the SK-1100 keyboard.
Most SG-1000s have a nameplate with blue trim, but some earlier consoles have black trim instead. These are colloquially known as the "Germany" models due to the nameplate's color scheme resembling the German flag.
Internally, the SG-1000 features rather flimsy construction with the single-sided main board only being held in by the four case screws. Alarmingly, the cartridge port is not properly secured to the board and is only held on by its solder joints. Due to the board being single-sided, it does not take much for the cartridge port to develop cracked solder joints, leading to poor reliability.
The original console also saw a release in New Zealand under the Grandstand brand, being released as the "Grandstand Sega 1000". These are mostly identical to the Japanese model save for the different nameplate and the use of a TMS9929 VDP, due to the lack of a PAL variant for the TMS9918 chip. These models have a separate board which converts the 9929's component video signals into composite, which is then fed into the RF modulator.
SG-1000 II (1984-1985)
A year after the SG-1000's debut, Sega released a revised model known as the SG-1000 II, which set out to correct some of the flaws from the original system. It is primarily a cosmetic redesign with no hardware upgrades, with the expansion port being relocated to the front of the console and a controller port for player one. On the top, the cartridge port is offset to the right with a small yellow pause button below it. At the back are the RF out, channel select, controller ports and power input. The console was also bundled with new joypad controllers which snap onto the sides of the console for storage.
The SG-1000 II saw two different board revisions over its short life, though these are not readily apparent without a teardown or trained eye. Build quality was improved compared to the original console, as the main board is screwed down on each side of the cartridge port, and the cartridge port itself is reinforced onto the board with rivets.
Early SG-1000 IIs feature identical hardware to the original console, including a TMS9918 VDP and SN76489 audio chip. At some point during production, Sega revised the SG-1000 II and replaced these two chips with the 315-5066, a custom chip designed by Yamaha. This board variant is especially notable in that the 315-5066 has unused RGB and sync outputs, meaning that these consoles can be easily modified for RGB output. Despite this, the color palette used by the 315-5066 is slightly inaccurate compared to a TMS9918. The number of VRAM chips was also reduced from eight to two with this board revision.