Sega CD (Model 2): Difference between revisions
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{{Infobox computer | {{Infobox computer | ||
| name = Sega CD Model 2<br />(Mega-CD 2) | | name = Sega CD Model 2<br />(Mega-CD 2) | ||
| image = [[File:Sega-CD- | | image = [[File:Sega-CD-Model2-Set.png|260px]] | ||
| caption = U.S. NTSC Sega CD (Model 2) side-mounted beneath a Genesis 2 | | caption = U.S. NTSC Sega CD (Model 2) side-mounted beneath a Genesis 2 | ||
| manufacturer = Sega Enterprises Ltd. | | manufacturer = Sega Enterprises Ltd. | ||
| Line 29: | Line 29: | ||
Launched '''April 1993''' in Japan and late-1993 overseas, it re-engineers the bulky front-loading Model 1 into a '''smaller, top-loading deck''' that bolts to the right-hand side of a Model-2 Genesis (or underneath a Model-1 via spacer plate). The redesign slashes build cost by integrating disc-logic, FM synth mix, and RF modulator into two new ASICs and by replacing the complex motorised tray with a spring-latched lid. | Launched '''April 1993''' in Japan and late-1993 overseas, it re-engineers the bulky front-loading Model 1 into a '''smaller, top-loading deck''' that bolts to the right-hand side of a Model-2 Genesis (or underneath a Model-1 via spacer plate). The redesign slashes build cost by integrating disc-logic, FM synth mix, and RF modulator into two new ASICs and by replacing the complex motorised tray with a spring-latched lid. | ||
== | == Historical Context & Sales == | ||
* Sega’s first CD drive – the '''Model 1 “front-loader”''' (HAA-2910) – cost US$299 and carried a high RMA rate (optical alignment, belt stretch). | * Sega’s first CD drive – the '''Model 1 “front-loader”''' (HAA-2910) – cost US$299 and carried a high RMA rate (optical alignment, belt stretch). | ||
* Cost-reduction taskforce (“MCD-R2”) produced a simplified mechanism using Sony’s ubiquitous '''KSS-210A''' pickup and a plastic clam-shell housing. | * Cost-reduction taskforce (“MCD-R2”) produced a simplified mechanism using Sony’s ubiquitous '''KSS-210A''' pickup and a plastic clam-shell housing. | ||
| Line 35: | Line 35: | ||
* Combined Model-1/2 worldwide sales ≈ '''2.24 million''' units – ~70 % are Model 2 according to 1995 Sega annual report. | * Combined Model-1/2 worldwide sales ≈ '''2.24 million''' units – ~70 % are Model 2 according to 1995 Sega annual report. | ||
== | == Hardware Architecture == | ||
{| class="wikitable" style="width:70%; text-align:center;" | {| class="wikitable" style="width:70%; text-align:center;" | ||
|+'''Major ICs (VA0 main-board)''' | |+'''Major ICs (VA0 main-board)''' | ||
| Line 80: | Line 80: | ||
|} | |} | ||
== | == Differences vs. Model 1 == | ||
{| class="wikitable" style="width: | {| class="wikitable" style="width:70%;" | ||
! Area !! Model 1 (1991) !! Model 2 (1993) !! Result | ! Area !! Model 1 (1991) !! Model 2 (1993) !! Result | ||
|- | |- | ||
| Line 95: | Line 95: | ||
|} | |} | ||
== | == External Connectors == | ||
* '''Expansion edge''' – identical 64-pin BUS as Model 1; ships with '''10 cm ribbon “mixing” cable''' to the Genesis 2 A/V port (carries left/right audio). | * '''Expansion edge''' – identical 64-pin BUS as Model 1; ships with '''10 cm ribbon “mixing” cable''' to the Genesis 2 A/V port (carries left/right audio). | ||
* '''AC Adaptor''' – same barrel 2.1 mm as Genesis 2 (centre positive). | * '''AC Adaptor''' – same barrel 2.1 mm as Genesis 2 (centre positive). | ||
* '''EXT Link''' – 9-pin mini-DIN to daisy-chain two Mega-CDs for dev use (never utilised by retail titles). | * '''EXT Link''' – 9-pin mini-DIN to daisy-chain two Mega-CDs for dev use (never utilised by retail titles). | ||
== | == Motherboard Revisions == | ||
{| class="wikitable" style="width:90%; text-align:center;" | {| class="wikitable" style="width:90%; text-align:center;" | ||
|+'''Mega-CD 2 Main-Boards''' | |+'''Mega-CD 2 Main-Boards''' | ||
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''All revisions are cross-compatible; BIOS ROM changes (v2.00→v2.11) fix '''Lunar Eternal Blue''' save bug and 32X pass-through timing.'' | ''All revisions are cross-compatible; BIOS ROM changes (v2.00→v2.11) fix '''Lunar Eternal Blue''' save bug and 32X pass-through timing.'' | ||
== | == Audio Path == | ||
1. RF5C164 PCM → 315-5880 bus → | 1. RF5C164 PCM → 315-5880 bus → | ||
2. ASIC mixer combines FM+PSG from Genesis via ribbon audio BUS → | 2. ASIC mixer combines FM+PSG from Genesis via ribbon audio BUS → | ||
| Line 120: | Line 120: | ||
Because mixing is line-level only, Model 2 inherits Genesis 2’s famous “quiet” output (~300 mVpp). Mods: VMU Audio Amp or “Sega CD Audio Boost” board (TL072). | Because mixing is line-level only, Model 2 inherits Genesis 2’s famous “quiet” output (~300 mVpp). Mods: VMU Audio Amp or “Sega CD Audio Boost” board (TL072). | ||
== | == Maintenance == | ||
* '''Pickup lens''' – KSS-210A rarely fails; clean with 91 % IPA swab. | * '''Pickup lens''' – KSS-210A rarely fails; clean with 91 % IPA swab. | ||
* '''Spindle hub''' – plastic hub cracks; 3-D-print “clamp hub saver” or cannibalise PC CD-ROM. | * '''Spindle hub''' – plastic hub cracks; 3-D-print “clamp hub saver” or cannibalise PC CD-ROM. | ||
* '''Lid switch''' – dual leaf SW1; adjust if unit reports “Please Close Cover” error. | * '''Lid switch''' – dual leaf SW1; adjust if unit reports “Please Close Cover” error. | ||
* '''Belt''' – Model 2 has *no belt*, only a direct-drive spindle. | * '''Belt''' – Model 2 has *no belt*, only a direct-drive spindle. | ||
* '''Capacitors''' – far fewer SMD cans: primarily C224 220 µF (5 V rail) and audio coupling 47 µF (C138, C139). See [[Sega CD Model 2 Capacitor Replacement Guide]]. | * '''Capacitors''' – far fewer SMD cans: primarily C224 220 µF (5 V rail) and audio coupling 47 µF (C138, C139). See [[Sega CD (Model 2) Capacitor Replacement Guide]]. | ||
== | == Common Faults & Fixes == | ||
{| class="wikitable" style="width:96%;" | {| class="wikitable" style="width:96%;" | ||
! Symptom !! Diagnosis !! Remedy | ! Symptom !! Diagnosis !! Remedy | ||
| Line 140: | Line 140: | ||
|} | |} | ||
== | == Popular Mods == | ||
* '''RGB Bypass''' via Triple-Bypass board (VDP → THS7374 → DIN 9). | * '''RGB Bypass''' via Triple-Bypass board (VDP → THS7374 → DIN 9). | ||
* '''Region Free BIOS''' – swap 27C1001 EPROM with patched ''Mega CD Multi-BIOS v2.8''. | * '''Region Free BIOS''' – swap 27C1001 EPROM with patched ''Mega CD Multi-BIOS v2.8''. | ||
| Line 146: | Line 146: | ||
* '''S-Video + Stereo Jack''' – tap Y/C from CXD2510Q and RF5C164 out. | * '''S-Video + Stereo Jack''' – tap Y/C from CXD2510Q and RF5C164 out. | ||
== | == Technical Documentation == | ||
* | * [[Sega CD 2 / Mega CD 2 - Service Manual]] – full schematics & test points. | ||
* Yasushi Yamaguchi, “Sega CD ASIC Architecture” – Nikkei 1994 conference slides. | * Yasushi Yamaguchi, “Sega CD ASIC Architecture” – Nikkei 1994 conference slides. | ||
* US Patent 5 471 206 – “Home-use CDROM system with rotation & scale processing”. | * US Patent 5 471 206 – “Home-use CDROM system with rotation & scale processing”. | ||
== | == Trivia & Pop-Culture == | ||
* Sega’s marketing touted Model 2 as “'''2 ½ times faster'''” to load due to firmware tweaks, though the drive itself is identical 1 × speed. | * Sega’s marketing touted Model 2 as “'''2 ½ times faster'''” to load due to firmware tweaks, though the drive itself is identical 1 × speed. | ||
* Film prop in ''Hackers'' (1995) – Acid Burn’s bedroom shows a Mega-CD 2 + Genesis 2 stack. | * Film prop in ''Hackers'' (1995) – Acid Burn’s bedroom shows a Mega-CD 2 + Genesis 2 stack. | ||
* The JP manual warns: “Do not place cup noodles on top lid while operating.” | * The JP manual warns: “Do not place cup noodles on top lid while operating.” | ||
== | == See Also == | ||
* [[Sega CD (Model 1)|Sega CD Model 1]] – original front-loader | * [[Sega CD (Model 1)|Sega CD Model 1]] – original front-loader | ||
* [[Sega Mega Drive / Genesis Model 2|Sega Genesis (Model 2)]] – matching base console | * [[Sega Mega Drive / Genesis Model 2|Sega Genesis (Model 2)]] – matching base console | ||
Latest revision as of 09:11, 12 May 2025
 | |
| U.S. NTSC Sega CD (Model 2) side-mounted beneath a Genesis 2 | |
| Specifications | |
|---|---|
| Manufacturer | Sega Enterprises Ltd. |
| Type | CD-ROM add-on console |
| Released | April 23, 1993 (JP Mega-CD 2) November 1, 1993 (US Sega CD 2) |
| Discontinued | 1996 (replaced by licensed JVC WonderMega 2 & CD X) |
| Intro price | JP ¥29 800 • US US$229 • EU £230 |
| CPU | Motorola MC68EC000 @ 12.500 MHz (main) Sony CXD1802Q custom gate-array (CD-DSP) † |
| Memory | 512 KB Program RAM 768 KB dual-ported Word-RAM 128 KB PCM Sample RAM 64 KB Battery-backed Save RAM |
| Storage | 1× 1 ×-speed top-loading CD-ROM (150 kB s⁻¹) cartridge passthrough up to 4 MB |
| Display | 256 / 320 × 224 px (NTSC) • 52-colour line-scroll • 80 sprites |
| Sound | Genesis YM3438 FM & PSG plus Ricoh RF5C164 8-ch PCM @ 32 kHz 10-bit DAC |
| Dimensions | 252 mm W × 215 mm D × 63 mm H |
| Weight | ≈ 1.3 kg |
| OS / Firmware | Mega-CD System BIOS v2.x (128 KB mask ROM) |
| Predecessor | Sega CD (Model 1) |
| Successor | Sega CDX / JVC Wondermega |
| Codename | • MARS-CD-B (JP R&D) • “Top-loader” |
| Model no. | HAA-2950 (JP) • MK-4102 (US) • MK-4102-50 (EU) |
The Sega CD Model 2 – known in Japan and PAL regions as the Mega-CD 2 – is the second-generation optical add-on for the Sega Genesis/Mega Drive. Launched April 1993 in Japan and late-1993 overseas, it re-engineers the bulky front-loading Model 1 into a smaller, top-loading deck that bolts to the right-hand side of a Model-2 Genesis (or underneath a Model-1 via spacer plate). The redesign slashes build cost by integrating disc-logic, FM synth mix, and RF modulator into two new ASICs and by replacing the complex motorised tray with a spring-latched lid.
Historical Context & Sales
[edit | edit source]- Sega’s first CD drive – the Model 1 “front-loader” (HAA-2910) – cost US$299 and carried a high RMA rate (optical alignment, belt stretch).
- Cost-reduction taskforce (“MCD-R2”) produced a simplified mechanism using Sony’s ubiquitous KSS-210A pickup and a plastic clam-shell housing.
- Debuted 23 April 1993 bundled with Sonic CD in Japan; U.S. release November 1993 bundled with Sewer Shark.
- Combined Model-1/2 worldwide sales ≈ 2.24 million units – ~70 % are Model 2 according to 1995 Sega annual report.
Hardware Architecture
[edit | edit source]| Part | Function(s) |
|---|---|
| MC68EC000 (64-pin) | Primary 16-bit CPU @ 12.5 MHz |
| 315-5880 “MCD ASIC 2” | Sub-CPU bus arbiter • Word-RAM controller • rotation / scaling / 3×3 matrix |
| 315-5788 | OKI MSM6295-compatible DMA + CD-SUB code ROM |
| Ricoh RF5C164 | 8-channel PCM generator, 10-bit DAC |
| CXD2510Q | CD-DSP / decoder – replaces discrete CN-303 & CXP controllers in Model 1 |
| 315-5684-B | RGB DAC + stereo mixer (shares with Genesis 2) |
Internally, software sees identical registers to Model 1; all games and dev tools remain compatible.
Clock Scheme (NTSC)
[edit | edit source]- Master XTAL = 12.500 MHz × 4 = 50.000 MHz → ÷4 = 12.5 MHz (68k)
- Z80 (in Genesis) still sourced from 53.693 MHz ÷15 ≈ 3.58 MHz
- Word-RAM dual-ported clock = 25 MHz.
Memory Map (MC68EC000)
[edit | edit source]| Range | Size | Device |
|---|---|---|
| $0000 00–$0FFF FF | 1 MB | Program RAM |
| $0200 00–$03FF FF | 2 MB | Word-RAM (dual-bank 0/1) |
| $0400 00–$05FF FF | 2 MB | PRG-RAM mirror / save RAM (battery) |
| $0600 00–$07FF FF | 2 MB | PCM sample RAM mirror |
| $0800 00–$0BFF FF | 4 MB | BIOS ROM (128 KB mirrored) |
| $0C00 00–$0DFF FF | 2 MB | CD-DSP & sub-CPU registers |
| $0E00 00–$0E00 FF | 256 B | Gate array I/O (gate, LEDs, reset) |
Differences vs. Model 1
[edit | edit source]| Area | Model 1 (1991) | Model 2 (1993) | Result |
|---|---|---|---|
| Drive mech | Sony KSS-240A sled + worm gear front-tray | Sony KSS-210A fixed sled, top-lid | 40 % cheaper, quieter |
| Optical control | CXP921P + CXD1095Q (DSP) | CXD2510Q SoC | Fewer PCB layers |
| Audio mixing | External op-amps, RCA output | Mixed inside 315-5684-B, no RCA | Shares Genesis 2 mini-DIN |
| Power rails | 9 V in → 5 V, –5 V, +12 V regulators | –5 V rail deleted (unused) | One less 7905 IC |
| Word-RAM width | 2 × 16-bit SRAM (dual bus) | Same, but SRAMs integrated in ASIC later VA1 | Slightly lower latency |
External Connectors
[edit | edit source]- Expansion edge – identical 64-pin BUS as Model 1; ships with 10 cm ribbon “mixing” cable to the Genesis 2 A/V port (carries left/right audio).
- AC Adaptor – same barrel 2.1 mm as Genesis 2 (centre positive).
- EXT Link – 9-pin mini-DIN to daisy-chain two Mega-CDs for dev use (never utilised by retail titles).
Motherboard Revisions
[edit | edit source]| Rev | Key ICs | Notes |
|---|---|---|
| VA0 | 315-5880, CXD2510Q, discrete SDRAM | Japan launch – green soldermask |
| VA1 | 315-5933 “ASIC 3” (RAM+gate array in one) | Most common US/EU; no Word-RAM wait glitches |
| VA2 (Majesco) | GOAC single-chip + Mitsubishi drive board | Pack-in with late Genesis 3; cost-reduced |
All revisions are cross-compatible; BIOS ROM changes (v2.00→v2.11) fix Lunar Eternal Blue save bug and 32X pass-through timing.
Audio Path
[edit | edit source]1. RF5C164 PCM → 315-5880 bus → 2. ASIC mixer combines FM+PSG from Genesis via ribbon audio BUS → 3. 315-5684-B internal op-amp → mini-DIN 9 (pins 2/4) / RCA L+R (PAL only). Because mixing is line-level only, Model 2 inherits Genesis 2’s famous “quiet” output (~300 mVpp). Mods: VMU Audio Amp or “Sega CD Audio Boost” board (TL072).
Maintenance
[edit | edit source]- Pickup lens – KSS-210A rarely fails; clean with 91 % IPA swab.
- Spindle hub – plastic hub cracks; 3-D-print “clamp hub saver” or cannibalise PC CD-ROM.
- Lid switch – dual leaf SW1; adjust if unit reports “Please Close Cover” error.
- Belt – Model 2 has *no belt*, only a direct-drive spindle.
- Capacitors – far fewer SMD cans: primarily C224 220 µF (5 V rail) and audio coupling 47 µF (C138, C139). See Sega CD (Model 2) Capacitor Replacement Guide.
Common Faults & Fixes
[edit | edit source]| Symptom | Diagnosis | Remedy |
|---|---|---|
| “Checking disc” endless | Spindle hub height / dirty lens | Clean lens; shim hub 0.2 mm |
| No PCM channels | RF5C164 pin-rot on VA0 | Re-flow QFP; recap C139/C140 |
| BIOS boots, drive dead | 5 V present, 9 V missing at CN3 | Replace poly-fuse PF1 or AC adaptor |
| 32X hangs on Sega CD | ASIC revision < v2.11 | Burn patch cart with “32X-SCD fix” |
Popular Mods
[edit | edit source]- RGB Bypass via Triple-Bypass board (VDP → THS7374 → DIN 9).
- Region Free BIOS – swap 27C1001 EPROM with patched Mega CD Multi-BIOS v2.8.
- Non-destructive Switchless – PIC16F630 toggles JP1/JP2 for 50/60 Hz & J/U/E.
- S-Video + Stereo Jack – tap Y/C from CXD2510Q and RF5C164 out.
Technical Documentation
[edit | edit source]- Sega CD 2 / Mega CD 2 - Service Manual – full schematics & test points.
- Yasushi Yamaguchi, “Sega CD ASIC Architecture” – Nikkei 1994 conference slides.
- US Patent 5 471 206 – “Home-use CDROM system with rotation & scale processing”.
Trivia & Pop-Culture
[edit | edit source]- Sega’s marketing touted Model 2 as “2 ½ times faster” to load due to firmware tweaks, though the drive itself is identical 1 × speed.
- Film prop in Hackers (1995) – Acid Burn’s bedroom shows a Mega-CD 2 + Genesis 2 stack.
- The JP manual warns: “Do not place cup noodles on top lid while operating.”
See Also
[edit | edit source]- Sega CD Model 1 – original front-loader
- Sega Genesis (Model 2) – matching base console
- Sega 32X – 32-bit attachment (Model 2 compatible)