Sega System 1/2


A system 1 board has been acquired in a working state for hardware testing and analysis. No hardware testing has been performed so far.


Refer to SegaRetro (System 1, System 2) and System16 (System 1, System 2) for a general hardware overview and list of games.

Hardware Components

I don’t believe the naming that’s currently applied to this hardware is correct. The terms “System 1” and “System 2” seem entirely made up by the emulation community, with no markings on the boards themselves identifying them in this way, nor the game flyers or manuals, or the schematics. The general information that’s commonly published providing system specifications for this hardware seems unsupported by actual references, and the division between System 1 and 2 games seems confusing and in some cases contradictory. It appears there may have been significant hardware variations between System 1/2 games, with at least six unique variations of main board layouts identifiable in the set of board photos provided below. Additionally, upgrade kits have been supplied in many cases, which provide daughter boards that extend the hardware for earlier main boards to support later games. It is true however that the many variations of boards are quite similar, and have the same primary hardware. The manual for the Wonder Boy conversion kit, released in 1986, suggests it was compatible with six hardware variations. With the currently available manuals and images, it appears there were at least the following main board variations:

This indicates at least four major board variants, with six minor revisions across those lines. There is not enough information currently available from the various online sources to clearly identify which games run on which hardware, and the prevalence of conversion kits with daughter boards further complicates matters. With the large number of board revisions, and lack of overall system identity and branding however, I’m not convinced this was ever considered as a formal general purpose hardware platform. It seems clear that there’s no distinct System 1 and System 2 hardware platforms, although there is a case to be made that all the various games released with similar and largely compatible hardware form a de-facto system of sorts. It appears likely that one first game was produced with a game-specific main board. To save time and costs however, that board was then re-used for other games. In some cases the board was used in an identical form, but in other cases the main board was revised to extend it slightly, for example to allow larger ROM sizes, or to add additional hardware, but still in a game-specific form. This approach had served Sega well in the past, no doubt reducing the up-front development time and costs for the first title, but with 30+ games released for this line of hardware, more than Sega had ever done before on an arcade platform, this approach would have ended up quite inefficient over time. It appears Sega ultimately found themselves revising the hardware once for approximately every three games they released. It seems highly likely that Sega’s experience with this hardware is what lead them to build formal general purpose platforms shortly afterwards. Having a flexible and extensible general purpose base board, with a switchable ROM board, allowed Sega to release many titles on a single hardware platform, reducing R&D costs over the life of the system and simplifying software development, while also making it easier for arcade operators to upgrade to new titles on the same platform.


       Code        Document Author Description Source
  Choplifter Schematics Sega Complete hardware schematics for Choplifter running on a 171-5303 main board. These are the original schematics from Sega. The schematics are clean, however slightly lower resolution than would be ideal. Some of the smaller labels are a bit hard to make out.
420-5110 Star Jacker Service Manual Sega Full service manual for StarJacker, including the board layout and schematics for the 171-5034 main board.
420-5270-91 Choplifter Instruction Manual Sega Choplifter conversion kit manual, with wiring diagram. 171-5303 or 171-5054-03 main board.
420-5295 Wonder Boy Instruction Manual Sega Wonder Boy conversion kit manual, with wiring diagram. 171-5034, 171-5054, 171-5154-01, 171-5054-02, 171-5054-03, or 171-5303-02 main board.
421-6057 Heavy Metal Dipswitch and Pinout Sega Heavy Metal dipswitch settings and pinout. 171-5303 or 171-5054-03 main board.
421-6113 My Hero Dipswitch and Pinout Sega My Hero dipswitch settings and pinout. 171-5034, 171-5054, 171-5054-01, 171-5054-02, or 171-5054-03 main board.
421-6178 Choplifter Dipswitch and Pinout Sega Choplifter dipswitch settings and pinout. 171-5303 or 171-5054-03 main board.
421-6285 Rafflesia Dipswitch and Pinout Sega Rafflesia dipswitch settings and pinout. 171-5034, 171-5054, 171-5054-01, 171-5054-02, or 171-5054-03 main board.
421-6307 Wonder Boy Dipswitch and Pinout Sega Wonder Boy dipswitch settings and pinout. 171-5034, 171-5054, 171-5154-01, 171-5054-02, 171-5054-03, or 171-5303-02 main board.
421-7289 UFO Senshi Yohko Chan Dipswitch and Pinout Sega UFO Senshi Yohko Chan dipswitch settings and pinout. 171-5303, 171-5303-01, or 171-5303-02 main board.
CN-112 Flicky Dipswitch and Pinout   Flicky dipswitch settings and pinout. Unofficial third party sheet.
  Wonder Boy II Dipswitch and Pinout   Wonder Boy II dipswitch settings and pinout. Unofficial third party sheet.
28-081300 Regulus Conversion Kit Technical Manual Wico Brief third party conversion kit instructions for Regulus.

High Resolution Photos


Miscellaneous Photos

Here’s a collection of images of this system that have been posted online from various sources: Hardware Photos