Sega CD (Model 1): Difference between revisions
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| name = Sega CD Model 1 ("Front-Loader") | | name = Sega CD Model 1 ("Front-Loader") | ||
| image = [[File:Sega-Genesis-CD-Model-1-Bare.jpg|260px]] | | image = [[File:Sega-Genesis-CD-Model-1-Bare.jpg|260px]] | ||
| caption = North-American Sega CD | | caption = North-American Sega CD Model 1 | ||
| manufacturer = Sega Enterprises Ltd.<br />Optical block by [[Sony]] (KSS-240A/KSS-240R) | | manufacturer = Sega Enterprises Ltd.<br />Optical block by [[Sony]] (KSS-240A/KSS-240R) | ||
| type = CD-ROM add-on console | | type = CD-ROM add-on console | ||
| release date | | release date = {{Start date|1991|12|12}} (JP Mega-CD)<br />{{Start date|1992|10|15}} (US Sega CD)<br />{{Start date|1993|05|01}} (EU Mega-CD) | ||
| discontinued = 1994 (superseded by Side-loader & Model 2) | | discontinued = 1994 (superseded by Side-loader & Model 2) | ||
| price = JP ¥49 800 • US US$299 • EU £270 | | price = JP ¥49 800 • US US$299 • EU £270 | ||
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| compatibility = Plays all Genesis/Mega Drive carts<br />Plays Sega CD/Mega-CD discs (region‐locked)<br />CD-Audio & CD+G graphics discs | | compatibility = Plays all Genesis/Mega Drive carts<br />Plays Sega CD/Mega-CD discs (region‐locked)<br />CD-Audio & CD+G graphics discs | ||
| predecessor = – (first Sega optical system) | | predecessor = – (first Sega optical system) | ||
| successor = [[Sega CD (Model 2) | | successor = [[Sega CD (Model 2)]] | ||
| codename = TMR-50 (Japan R&D), “Topaz” (US) | | codename = TMR-50 (Japan R&D), “Topaz” (US) | ||
| model = HAA-2910 (JP), MK-1601 (US), MK-1690-50 (EU) | | model = HAA-2910 (JP), MK-1601 (US), MK-1690-50 (EU) | ||
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Released in late 1991, it augmented the base console with a faster 12.5 MHz 68EC000, hardware scaling/rotation ASICs, 8-channel PCM audio and the ability to stream full-motion video (Cinepak) from CD-ROM. | Released in late 1991, it augmented the base console with a faster 12.5 MHz 68EC000, hardware scaling/rotation ASICs, 8-channel PCM audio and the ability to stream full-motion video (Cinepak) from CD-ROM. | ||
== | == Historical context & sales == | ||
* '''Concept (1989–1990):''' Sega R&D2 (Hisashi Suzuki) partnered with Sony Devices Div. to adopt the KSS-240 laser deck. | * '''Concept (1989–1990):''' Sega R&D2 (Hisashi Suzuki) partnered with Sony Devices Div. to adopt the KSS-240 laser deck. | ||
* '''Launch:''' 12 Dec 1991, JP ¥49 800 – initial shipment 100 k; supply shortages until Feb 1992. | * '''Launch:''' 12 Dec 1991, JP ¥49 800 – initial shipment 100 k; supply shortages until Feb 1992. | ||
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* '''Total Model 1 units:''' ≈ 600 k worldwide (of 2.2 M total Sega CD family). | * '''Total Model 1 units:''' ≈ 600 k worldwide (of 2.2 M total Sega CD family). | ||
== | == Architecture overview == | ||
{| class="wikitable styled-table" style="width:70%; text-align:center;" | {| class="wikitable styled-table" style="width:70%; text-align:center;" | ||
! Sub-system !! IC(s) !! Notes | ! Sub-system !! IC(s) !! Notes | ||
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|} | |} | ||
== | == Technical specification (Model 1, BIOS v1.10) == | ||
{| class="wikitable styled-table" style="width:70%; text-align:center;" | {| class="wikitable styled-table" style="width:70%; text-align:center;" | ||
|- | |- | ||
! | ! style="background:#ddd;" |Processing | ||
|- | |- | ||
| Main 68k | 12.500 MHz (25 MHz ÷ 2) wait-stated 3–4 cycles to word-RAM | | Main 68k | 12.500 MHz (25 MHz ÷ 2) wait-stated 3–4 cycles to word-RAM | ||
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| DMA | 5.0 MB·s⁻¹ peak host⇄word-RAM | | DMA | 5.0 MB·s⁻¹ peak host⇄word-RAM | ||
|- | |- | ||
! | ! style="background:#ddd;" |Memory map (simplified) | ||
|- | |- | ||
| $0000 00–$1F FFFF | 2 MB Program RAM | | $0000 00–$1F FFFF | 2 MB Program RAM | ||
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* V-blank interrupt every 262 lines NTSC (≈ 59.92 Hz). | * V-blank interrupt every 262 lines NTSC (≈ 59.92 Hz). | ||
== | == Pin-by-pin expansion bus == | ||
The 50-pin edge (CN-B) carries the Genesis 68000 bus plus additional DMA and audio lines: | The 50-pin edge (CN-B) carries the Genesis 68000 bus plus additional DMA and audio lines: | ||
{| class="wikitable styled-table" style="width: | {| class="wikitable styled-table" style="width:70%;" | ||
! Pin !! Dir !! Name !! Description | ! Pin !! Dir !! Name !! Description | ||
|- | |- | ||
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| B49 || – || +5 V || | | B49 || – || +5 V || | ||
|- | |- | ||
| B50 | – | GND | | | B50 || – || GND || | ||
|} | |} | ||
Full table with all 50 pins on [[Mega Drive expansion port pinout]]. | Full table with all 50 pins on [[Mega Drive expansion port pinout]]. | ||
== | == Known hardware revisions & PCB errata == | ||
{| class="wikitable styled-table" style="width:90%; text-align:center;" | {| class="wikitable styled-table" style="width:90%; text-align:center;" | ||
! Assy # !! Board silk !! Region !! Notable changes / bugs !! Service fixes | ! Assy # !! Board silk !! Region !! Notable changes / bugs !! Service fixes | ||
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|- | |- | ||
| 171-5978B || VA1 || US | BIOS 1.10, word-RAM wait fix || Add R511 pull-up (factory bodge) | | 171-5978B || VA1 || US | BIOS 1.10, word-RAM wait fix || Add R511 pull-up (factory bodge) | ||
| | |||
|- | |- | ||
| 171-5978C || VA2 || EU | CXD1162 rev-C, 315-5548A ASIC || 74HC00 (IC15) ESD prone – replace with HCT | | 171-5978C || VA2 || EU | CXD1162 rev-C, 315-5548A ASIC || 74HC00 (IC15) ESD prone – replace with HCT | ||
| | |||
|} | |} | ||
== | == Common failure points == | ||
* '''“GREEN LED but no spin”''' – blown surface-mount fuse F301 (2 A) or shorted 5 V tantalum C230. | * '''“GREEN LED but no spin”''' – blown surface-mount fuse F301 (2 A) or shorted 5 V tantalum C230. | ||
* '''Tray won’t eject / belt slip''' – 40 mm × 1.2 mm neoprene belt hardened. Replace with 41 mm 0.6 mm square belt. | * '''Tray won’t eject / belt slip''' – 40 mm × 1.2 mm neoprene belt hardened. Replace with 41 mm 0.6 mm square belt. | ||
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* '''Backup RAM corrupt''' – CR2032 coin cell dead or IC3 SRM2016 failing. | * '''Backup RAM corrupt''' – CR2032 coin cell dead or IC3 SRM2016 failing. | ||
== | == Service manuals & schematics == | ||
* [[Sega CD Service Manual|Sega Service Document #170-0436-01]] | * [[Sega CD Service Manual|Sega Service Document #170-0436-01]] | ||
== | == General maintenance == | ||
Full disassembly, recap lists and belt change procedure: see [[Sega CD (Model 1) | Full disassembly, recap lists and belt change procedure: see [[Sega CD (Model 1) Maintenance Guide]]. | ||
Capacitor map and polarity silks are on [[Sega CD (Model 1) Capacitor Replacement Guide]]. | Capacitor map and polarity silks are on [[Sega CD (Model 1) Capacitor Replacement Guide]]. | ||
== | == Troubleshooting == | ||
A step-by-step power-on diagnostic flow (LED blink codes, fuse chart, clock probing) is available on [[Sega CD (Model 1) Troubleshooting Guide]]. | A step-by-step power-on diagnostic flow (LED blink codes, fuse chart, clock probing) is available on [[Sega CD (Model 1) Troubleshooting Guide]]. | ||
== | == Audio/Video modifications == | ||
* Direct-mix “board-jail”: lift R171 &R172, route RF5C164 output to Genesis EXT stereo jack – no crosstalk. | * Direct-mix “board-jail”: lift R171 &R172, route RF5C164 output to Genesis EXT stereo jack – no crosstalk. | ||
* RGB bypass: use Genesis VDP RGB; Sega CD adds no extra graphics plane, so standard MD RGB mod applies. | * RGB bypass: use Genesis VDP RGB; Sega CD adds no extra graphics plane, so standard MD RGB mod applies. | ||
* 50/60 Hz region switch – tie ASIC pin 4 ‘AREA’ to DIP switch + patch BIOS byte $1FE1. | * 50/60 Hz region switch – tie ASIC pin 4 ‘AREA’ to DIP switch + patch BIOS byte $1FE1. | ||
== | == Software & homebrew == | ||
Model 1 BIOS 1.10 supports '''CD-R''' if session is MODE1+CDDA (avoid 40× burns). Recommended test suites: ‘’Sega CD Test Disc’’ by discedge; ‘’RAM Stress’’ by Luke Usher. | Model 1 BIOS 1.10 supports '''CD-R''' if session is MODE1+CDDA (avoid 40× burns). Recommended test suites: ‘’Sega CD Test Disc’’ by discedge; ‘’RAM Stress’’ by Luke Usher. | ||
== | == Trivia & pop-culture == | ||
* ‘’Snatcher’’ (JP) used SCD PCM channels for full Japanese voice acting – a first on 8 Mbit disc. | * ‘’Snatcher’’ (JP) used SCD PCM channels for full Japanese voice acting – a first on 8 Mbit disc. | ||
* The launch bundle ‘’Sol-Feace’’ shipped on both cart (JP) and CD; players compared load-times as marketing. | * The launch bundle ‘’Sol-Feace’’ shipped on both cart (JP) and CD; players compared load-times as marketing. | ||