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{{Infobox computer
{{Infobox computer
| name          = Sega CD Model 1 / Mega-CD
| name          = Sega CD Model 1 / Mega-CD
| image        = [[File:Sega Mega CD main board 837-8015-01 parts location.png|260px]]
| image        = [[File:Sega CD Model 1.jpg|260px|frameless]]
| caption      = Sega's mount diagram for the Mega-CD main board
| caption      = A Model 1 Sega CD with the steel joining plate fitted
| manufacturer  = Sega Enterprises, Ltd.
| manufacturer  = Sega Enterprises, Ltd.
| type          = CD-ROM add-on for the [[Sega Mega Drive / Genesis (Model 1)|Mega Drive / Genesis]]
| type          = CD-ROM add-on for the [[Sega Mega Drive / Genesis (Model 1)|Mega Drive / Genesis]]
| release date = 12 December 1991 (JP)<br />11 November 1992 (US)<br />2 April 1993 (UK)<ref name="sr_mcd">Sega Retro, ''Sega Mega-CD'', https://segaretro.org/Mega-CD — release dates, prices and Sega model codes, each footnoted to a contemporary source on that page. Secondary source.</ref>
| release_date = 12 December 1991 (Japan)<br />15 October 1992 (North America)<br />2 April 1993 (UK)<ref name="wpsegacd">{{cite web |url=https://en.wikipedia.org/wiki/Sega_CD |title=Sega CD |website=Wikipedia |access-date=2026-10-01}} Secondary source; the dates and prices are cited there to Sega's own Mega-CD page, ''Retro Gamer'' issue 153 and ''Computer and Video Games'' issue 138, p. 8.</ref>
| price        = ¥49,800 (JP) • US$299.95 (US) • £269.99 (UK)<ref name="sr_mcd" />
| price        = ¥49,800 (Japan), US$299 (North America), £269.99 (UK)<ref name="wpsegacd" />
| model        = HAA-2910 (JP) • 1690 (US) • 1690-18 (UK)<ref name="sr_mcd" />
| cpu          = 68HC000 at 12.5 MHz (sub CPU), fitted as MC68HC000FN12, HD68HC000CP-12 or TMP68HC000T-12<ref name="mcd1pl">Sega Enterprises, Ltd., ''MEGA-CD Maintenance Manual'' (Export), August 1992, Rev. A, section 8, parts lists for main board 837-8952 (PDF pp. 94-96), sub board 837-8953 (pp. 97-98) and connect board 839-0534 (p. 99). See [[Sega CD Service Manual]].</ref>
| cpu          = 68HC000 at 12.5&nbsp;MHz (sub CPU); fitted as MC68HC000FN12, HD68HC000CP-12 or TMP68HC000T-12<ref name="mcd1man">Sega Enterprises, Ltd., ''Mega-CD Maintenance Manual'' (Export / Europe), August 1992, Rev. A — hosted on this wiki as [[:File:Sega CD Service Manual.pdf]] (see [[Sega CD Service Manual]]). Section 2-3 is the disassembly procedure, section 3 the spare parts list, section 4 the accessories list, section 5 Sega’s own PCB repair flow chart, section 8 the parts lists for the 837-8952 main board, 837-8953 sub board and 839-0534 connect board, and sections 9–10 the schematics and mount diagrams.</ref>
| memory        = 4 Mbit program RAM, 2 × 1 Mbit word RAM, 64K × 8 PCM RAM, 16K × 8 CD-ROM buffer, 8K × 8 back-up RAM<ref name="mcd1bd">Sega Enterprises, ''MEGA-CD Maintenance Manual'' (Export), August 1992, Rev. A, section 1, block diagram (PDF p. 5, "MEGA-CD HARD MANUAL", Ver. 0.5, 2 July 1991). See [[Sega CD Service Manual]].</ref>
| memory        = 4&nbsp;Mbit program RAM • 2 × 1&nbsp;Mbit word RAM • 64&nbsp;K × 8 PCM RAM • 16&nbsp;K × 8 CD decoder SRAM • 8&nbsp;K × 8 battery-backed RAM<ref name="mcd1man" />
| storage      = Single-speed CD-ROM drive unit, Sony KSK-1200A or JVC ELM-135<ref name="mcd1asm">Sega Enterprises, ''MEGA-CD Maintenance Manual'' (Export), August 1992, Rev. A, section 2-2 assembly lists (assembly 1006, PDF pp. 19-20), section 2-3 disassembly and assembly procedure (pp. 23-24) and section 3 spare parts list (p. 26). See [[Sega CD Service Manual]].</ref>
| storage      = Single-speed CD-ROM drive unit (Sony KSK-1200A or JVC ELM-135)<ref name="mcd1man" />
| display      = None; video is produced by the Mega Drive
| sound        = Ricoh RF5C164A (315-5476A) 8-channel PCM, LC7883KM digital filter and LC7881M DAC<ref name="mcd1man" />
| sound        = Ricoh RF5C164A (Sega 315-5476A) 8-channel PCM, with LC7881 and LC7883 D/A converters<ref name="mcd1bd" /><ref name="mcd1pl" />
| power        = External AC adaptor, 10&nbsp;V DC at 1.2&nbsp;A<ref name="mcd1man" />
| power        = External AC adaptor, 10 V DC 1.2 A<ref name="mcd1acc">Sega Enterprises, ''MEGA-CD Maintenance Manual'' (Export), August 1992, Rev. A, section 4, accessories list for Europe (PDF p. 28). See [[Sega CD Service Manual]].</ref>
| os            = Boot ROM, 1&nbsp;Mbit (EPR-15045 / MPR-15045)<ref name="mcd1man" />
| os            = 1 Mbit boot ROM, EPR-15045 or MPR-15045<ref name="mcd1bd" /><ref name="mcd1pl" />
| predecessor  = —
| successor    = [[Sega CD (Model 2)]]
| successor    = [[Sega CD (Model 2)]]
}}
}}
<templatestyles src="Template:StyledTable/styles.css" />
<templatestyles src="Template:StyledTable/styles.css" />


The '''Sega CD Model 1''' — sold in Japan and Europe as the '''Mega-CD''' — is the original front-loading compact-disc add-on for the [[Sega Mega Drive / Genesis (Model 1)|Mega Drive / Genesis]]. It bolts to the right-hand expansion port, sits under the console, and adds a second 68000, more RAM, hardware scaling and rotation, eight channels of PCM audio and a CD-ROM drive.<ref name="sr_mcd" />
The '''Sega CD Model 1''', sold as the '''Mega-CD''' outside North America, is Sega's original front-loading CD-ROM add-on for the [[Sega Mega Drive / Genesis (Model 1)|Mega Drive and Genesis]]. It sits under the console, connects through the console's expansion port and adds a second 68000 CPU, more RAM, a custom graphics chip with scaling and rotation, eight-channel PCM sound and a CD drive with a motorised tray.<ref name="wpsegacd" /> It produces no video of its own, and it has its own mains adaptor.


It is not a stand-alone machine and it does not generate video: everything reaches the television through the Mega Drive. It does, however, need its own mains adaptor, so a Mega Drive plus Mega-CD occupies two sockets.<ref name="sr_mcd" />
== History ==
 
Sega released the Mega-CD in Japan on 12 December 1991 at ¥49,800. It reached North America as the Sega CD on 15 October 1992 at US$299, and the UK on 2 April 1993 at £269.99. Sega followed it with the smaller, top-loading [[Sega CD (Model 2)|Model 2]], released in Japan on 23 April 1993 to bring down manufacturing costs.<ref name="wpsegacd" />


== Architecture ==
== Architecture ==


Sega's block diagram for the machine (reproduced in the maintenance manual, dated 1991) shows the following.<ref name="mcd1man" />
Sega's block diagram, dated 2 July 1991, shows the following blocks.<ref name="mcd1bd" /> Board positions are from the parts list for the export main board, 837-8952.<ref name="mcd1pl" />


{| class="wikitable styled-table" style="width:80%;"
{| class="wikitable styled-table" style="width:70%; text-align:left;"
! Block !! Device !! Notes
|+'''Main functional blocks'''
! Block !! Device (export main board) !! Notes
|-
|-
| Sub CPU || 68HC000 at 12.5 MHz || Second-source part: Motorola, Hitachi or Toshiba. Runs from the boot ROM and the program RAM; the Mega Drive's own 68000 remains the main CPU
| Sub CPU || IC1, 68HC000 at 12.5 MHz || Runs from the boot ROM and program RAM. The Mega Drive's own 68000 remains the main CPU
|-
|-
| Gate array || Sega 315-5548, "custom chip MCE2" (Fujitsu MB634120) || Labelled ''MEGA-CD ENGINE'' on the block diagram. Arbitrates the two CPUs, drives both word-RAM banks, and carries the scaling and rotation hardware
| Gate array || IC2, Sega 315-5548 "custom chip MCE2" (Fujitsu MB634120) || Labelled MEGA-CD ENGINE on the block diagram. Connects both CPUs, the word RAM, the CD-ROM decoder and the PCM chip
|-
|-
| Boot ROM || EPR-15045 / MPR-15045, 1 Mbit || CD game BIOS, CD player software and CD+G support
| Boot ROM || IC4, EPR-15045 or MPR-15045, 1 Mbit || In a 40-pin socket
|-
|-
| Program RAM || 4 Mbit || Sub-CPU workspace
| Program RAM || IC5, µPD424270, 4 Mbit ||
|-
|-
| Word RAM || 2 × 1 Mbit (WORD-RAM 0, WORD-RAM 1) || Shared between the two CPUs by the gate array
| Word RAM || IC7 and IC8, TC511664, 1 Mbit each || WORD-RAM 0 and WORD-RAM 1
|-
|-
| PCM sound || Ricoh RF5C164A (Sega 315-5476A) with 64 K × 8 wave RAM || Eight channels
| PCM sound || IC3, Ricoh RF5C164A (Sega 315-5476A), with IC10 and IC11 (64K × 8 wave RAM) || Eight channels
|-
|-
| CD decoder || Sanyo LC8951 with 16 K × 8 SRAM || Error correction and CD-ROM data handling
| CD-ROM decoder || IC13, Sanyo LC8951, with IC14 and IC15 (16K × 8 buffer) || Error correction for CD-ROM data
|-
|-
| Backup RAM || 8 K × 8, battery-backed || Saves; the cell is fitted on the main board
| Back-up RAM || IC16, MB8464A, 8K × 8 || Held up by the cell BT on the main board
|-
|-
| CD audio path || LC7883KM digital filter → LC7881M DAC → µPC844 op-amps → 20 kHz low-pass and 4 kHz pre-emphasis → LINE OUT || All on the sub board
| Audio || Sub board: LC7883 and LC7881 D/A converters, µPC844 op-amps || CD audio from the drive goes through the LC7883; PCM goes through the LC7881 and a low-pass filter. The two are mixed, filtered at 20 kHz and sent to the LINE OUT jacks
|-
|-
| Clock || 50 MHz crystal oscillator || On the main board
| Clock || 50 MHz crystal oscillator ||
|}
|}
The CD drive itself is a complete purchased assembly and Sega's parts lists do not break it down into components.<ref name="mcd1man" />


== Boards ==
== Boards ==


The machine is built from three boards plus the drive unit. Sega's export manual carries parts lists for the export boards and mount diagrams for the earlier Japanese boards, so both sets are documented.<ref name="mcd1man" />
The unit has three boards and a drive unit. The export manual gives parts lists for the export boards and carries Sega's schematics and mount diagrams, which are drawn for the earlier main board 837-8015-01 and sub board 837-8046-01.<ref name="mcd1pl" /><ref name="c5cd1">{{cite web |url=https://wiki.console5.com/wiki/Sega_CD_v1 |title=Sega CD v1 |website=Console5 TechWiki |access-date=2026-10-01}} Secondary source: IC lists and capacitor lists read off real boards, including the earlier Japanese boards and both drive PCBs.</ref>


{| class="wikitable styled-table" style="width:90%;"
{| class="wikitable styled-table" style="width:70%; text-align:left;"
! Board !! Export assembly !! Earlier Japanese assembly !! Function
|+'''Boards and drive units'''
! Board !! Export assembly !! Earlier assembly !! What it carries
|-
|-
| Main || 837-8952 (PCB 171-6326A) || 837-8015-01 || Sub CPU, gate array, all RAM, boot ROM, CD decoder, PCM, backup cell
| Main || 837-8952 (PCB 171-6326A) || 837-8015-01 || Sub CPU, gate array, all RAM, boot ROM, CD-ROM decoder, PCM chip, back-up cell, LEDs
|-
|-
| Sub || 837-8953 (PCB 171-6327A) || 837-8046-01 || DC input, fuse, 5 V regulator, CD audio DAC and output stage, MIX IN and LINE OUT jacks
| Sub || 837-8953 (PCB 171-6327A) || 837-8046-01 || DC input, fuse, 5 V regulator, audio D/A converters and output stage, MIX and LINE OUT jacks
|-
|-
| Connect || 839-0534 (PCB 171-6328A) || 837-8326 / 837-8327-01<ref name="c5cd1">console5 TechWiki, ''Sega CD v1'', https://wiki.console5.com/wiki/Sega_CD_v1 . Secondary source — a community capacitor map read off real boards. Its lists for the 837-8952 main board and the 837-8953 sub board agree position for position with Sega’s own parts list, and it adds the Japanese-revision boards and the two CD-ROM PCBs, which Sega’s export manual does not itemise.</ref> || Carries the 60-pin edge connector to the console
| Connect || 839-0534 (PCB 171-6328A) || 837-8326 or 837-8327-01 || The 60-pin edge connector to the console
|-
|-
| Drive unit || 610-5270 (Sony KSK-1200A) or 610-5270-10 (JVC ELM-135) || — || Complete CD mechanism, servo and pickup
| Drive unit || 610-5270 (Sony KSK-1200A) or 610-5270-10 (JVC ELM-135) || || Complete CD mechanism, servo and pickup
|}
|}


The two drive units are genuinely different mechanisms. The Sony KSK-1200A carries a KSS-240A pickup; the JVC deck (PCB EMW10258 / ENN-335A-1) carries an Optima-5S.<ref name="c5cd1" /> Identify which one you have before ordering a pickup or a capacitor kit.
Console5 records the Sony KSK-1200A with a KSS-240A pickup and the JVC drive (PCB EMW10258 / ENN-335A-1) with an Optima-5S pickup. The two mechanisms share no parts.<ref name="c5cd1" />
 
The connect board is worth noting: the export 839-0534 board carries eighteen 150 pF ceramic chip capacitors and no electrolytics at all, while the earlier Japanese connect boards do carry electrolytics.<ref name="mcd1man" /><ref name="c5cd1" />


== Power ==
== Power ==


The Model 1 is powered by its own external adaptor, not from the console. Sega's accessories list for Europe specifies '''10 V DC at 1.2 A''': parts 400-5122A and 400-5122B for 220 V mains and 400-5127 and 400-5127A for 240 V mains.<ref name="mcd1man" /> The Model 2 uses an adaptor of the same rating.<ref name="mcd2man">Sega Enterprises, Ltd., ''Sega CD II / Mega CD II Service Manual, No. 002'', August 1993 — hosted on this wiki as [[:File:Sega cd 2 - mega cd 2 - service manual.pdf]] (see [[Sega CD 2 / Mega CD 2 - Service Manual]]). Section 1 gives the ratings, section 3 the disassembly, section 4 the CD drive adjustments, section 5 the CD interface, section 7 the TOC read-in flow chart, section 8 the focus, tracking, disc and feed servicing flow charts, and section 13-3 the electrical parts list.</ref>
The Model 1 has its own external adaptor. Sega's accessories list for Europe gives 400-5122A and 400-5122B for 220 V mains and 400-5127 and 400-5127A for 240 V, all 10 V DC at 1.2 A.<ref name="mcd1acc" /> On the sub board the DC input goes through fuse F1, a Pico II 2.5 A radial part, and diode D1 to IC6, a µPC2405HF 5 V regulator on a heat sink.<ref name="mcd1pl" /><ref name="c5cd1" />
 
Inside, the sub board takes the DC in through fuse '''F1''' — a Pico II 2.5 A radial part — and a series diode, and regulates it to 5 V with a µPC2405 switching regulator at IC6.<ref name="mcd1man" /><ref name="c5cd1" /> The main board carries an MB3790 supply monitor at IC6, which is also the backup-cell controller.<ref name="mcd1man" />
 
A great many "dead Sega CD" reports are the adaptor rather than the machine. Sega's own repair flow chart begins there: if the unit will not power on, the branches it offers are a faulty AC adaptor, a faulty plug cord, a faulty Mega Drive or a faulty sub board — the main board is not on that branch at all.<ref name="mcd1man" />


== Servicing ==
== Servicing ==


Sega's PCB repair flow chart divides faults by what you see on screen.<ref name="mcd1man" />
Sega's PCB repair flow chart works at module level.<ref name="mcd1fc">Sega Enterprises, ''MEGA-CD Maintenance Manual'' (Export), August 1992, Rev. A, section 5, PCB repair flow chart (PDF p. 30). See [[Sega CD Service Manual]].</ref> With no picture and no power, it blames the AC adaptor or the sub board. With a picture, it sends a missing CD-ROM screen to the main board or the Mega Drive, a tray that will not open or shut to the CD drive unit, no sound to the FFC cable between the main and sub boards, and a mixing fault to the plug cord or the Mega Drive. The drive unit is a complete assembly with a single Sega part number, and the manual gives no adjustment procedure for it.<ref name="mcd1asm" />


* '''Picture appears, but no CD-ROM command displayed''' — main board or Mega Drive.
The electrolytic capacitors are the usual age fault: twelve on the export main board, ten of them surface-mount, and eighteen on the sub board.<ref name="mcd1pl" /> See the [[Sega CD (Model 1) Capacitor Replacement Guide]] for the list, the [[Sega CD (Model 1) Troubleshooting Guide]] for fault finding and the [[Sega CD (Model 1) Maintenance Guide]] for strip-down and cleaning.
* '''Tray will not open or shut''' — CD drive unit; the remedy given is to change the drive unit.
* '''No sound''' — CD unit, the Mega-CD audio side, or the FFC cable between the main and sub boards.
* '''Sound present but mixing faulty''' — the plug cord, or the Mega Drive.
* '''No power''' — AC adaptor, plug cord, Mega Drive or sub board.


Two mechanical details follow from the construction. Everything inside the drive unit — belt, gears, sled, tray motor, spindle — is supplied only as part of the complete assembly, so none of it has a published Sega part number; and because the assembly is an ordinary Sony or JVC CD deck, those are the part numbers to search on when sourcing mechanical spares.<ref name="mcd1man" />
== Things that are not faults ==


Age faults on this machine are dominated by its aluminium electrolytics. The ten on the export main board are surface-mount chip parts and the fourteen on the sub board are radial; leakage from the surface-mount parts, and the board damage that follows it, is the reason console5 files this machine under bad capacitors.<ref name="c5cd1" /> Full lists, per board, are on [[Sega CD (Model 1) Capacitor Replacement Guide]]; symptom-by-symptom diagnosis is on [[Sega CD (Model 1) Troubleshooting Guide]]; strip-down and cleaning are on [[Sega CD (Model 1) Maintenance Guide]].
* No picture from the Mega-CD on its own. It has no video output.
* No CD sound through the television with a Model 1 Mega Drive. The CD unit's sound comes out of its own LINE OUT jacks; to hear the console and the CD together, the Mega Drive's headphone output is cabled into the input jack on the back of the CD unit and the mixed sound is taken from the CD unit. A Model 2 console does not need the cable.<ref name="wpsegacd" />
* Two mains adaptors. The add-on has its own by design.


== Things that are not faults ==
== Documentation ==


* '''No picture of its own.''' The Model 1 outputs no video. A blank screen with the Mega-CD attached is a Mega Drive, cable or television fault until proved otherwise.
* [[Sega CD Service Manual]]: Sega's ''MEGA-CD Maintenance Manual'' (Export), August 1992, Rev. A, with parts lists, schematics, mount diagrams, the repair flow chart and the check-cartridge error list.
* '''Needing the mixing cable.''' CD audio leaves the Mega-CD on its own LINE OUT phono jacks and is fed back into the Mega Drive; on a Model 1 Mega Drive that route is the console's headphone socket.<ref name="sr_mcd" /> Without that cable you get cartridge sound and no CD sound, and nothing is broken.
* [[Mega CD / Sega CD Schematics]]: larger A3 scans of the block diagram of the 315-5548, the schematics and the main board mount diagrams.
* '''Two mains sockets.''' The add-on has its own adaptor by design.<ref name="sr_mcd" />
* [[Sega IC Specifications (Genesis VA7, Mega Drive VA6.5, Mega CD)]]: Sega's IC pin data for this family.


== Documentation ==
== Gallery ==


* [[Sega CD Service Manual]] — ''Mega-CD Maintenance Manual'' (Export / Europe), August 1992, Rev. A.
<gallery mode="packed" heights="200">
* [[Mega CD / Sega CD Schematics]] — A3 schematic sheets.
File:Sega Mega CD main board 837-8015-01 parts location.png|Sega's mount diagram for the main board 837-8015-01
* [[Sega IC Specifications (Genesis VA7, Mega Drive VA6.5, Mega CD)]] — Sega's IC data for this family.
File:Sega Mega CD sub board 837-8046-01 parts location.png|Sega's mount diagram for the sub board 837-8046-01
</gallery>


== Related pages ==
== Related pages ==

Latest revision as of 10:43, 6 October 2026

Sega CD Model 1 / Mega-CD
A Model 1 Sega CD with the steel joining plate fitted
Specifications
ManufacturerSega Enterprises, Ltd.
TypeCD-ROM add-on for the Mega Drive / Genesis
Released12 December 1991 (Japan)
15 October 1992 (North America)
2 April 1993 (UK)[1]
Intro price¥49,800 (Japan), US$299 (North America), £269.99 (UK)[1]
CPU68HC000 at 12.5 MHz (sub CPU), fitted as MC68HC000FN12, HD68HC000CP-12 or TMP68HC000T-12[2]
Memory4 Mbit program RAM, 2 × 1 Mbit word RAM, 64K × 8 PCM RAM, 16K × 8 CD-ROM buffer, 8K × 8 back-up RAM[3]
StorageSingle-speed CD-ROM drive unit, Sony KSK-1200A or JVC ELM-135[4]
DisplayNone; video is produced by the Mega Drive
SoundRicoh RF5C164A (Sega 315-5476A) 8-channel PCM, with LC7881 and LC7883 D/A converters[3][2]
PowerExternal AC adaptor, 10 V DC 1.2 A[5]
OS / Firmware1 Mbit boot ROM, EPR-15045 or MPR-15045[3][2]
SuccessorSega CD (Model 2)

The Sega CD Model 1, sold as the Mega-CD outside North America, is Sega's original front-loading CD-ROM add-on for the Mega Drive and Genesis. It sits under the console, connects through the console's expansion port and adds a second 68000 CPU, more RAM, a custom graphics chip with scaling and rotation, eight-channel PCM sound and a CD drive with a motorised tray.[1] It produces no video of its own, and it has its own mains adaptor.

History

[edit | edit source]

Sega released the Mega-CD in Japan on 12 December 1991 at ¥49,800. It reached North America as the Sega CD on 15 October 1992 at US$299, and the UK on 2 April 1993 at £269.99. Sega followed it with the smaller, top-loading Model 2, released in Japan on 23 April 1993 to bring down manufacturing costs.[1]

Architecture

[edit | edit source]

Sega's block diagram, dated 2 July 1991, shows the following blocks.[3] Board positions are from the parts list for the export main board, 837-8952.[2]

Main functional blocks
Block Device (export main board) Notes
Sub CPU IC1, 68HC000 at 12.5 MHz Runs from the boot ROM and program RAM. The Mega Drive's own 68000 remains the main CPU
Gate array IC2, Sega 315-5548 "custom chip MCE2" (Fujitsu MB634120) Labelled MEGA-CD ENGINE on the block diagram. Connects both CPUs, the word RAM, the CD-ROM decoder and the PCM chip
Boot ROM IC4, EPR-15045 or MPR-15045, 1 Mbit In a 40-pin socket
Program RAM IC5, µPD424270, 4 Mbit
Word RAM IC7 and IC8, TC511664, 1 Mbit each WORD-RAM 0 and WORD-RAM 1
PCM sound IC3, Ricoh RF5C164A (Sega 315-5476A), with IC10 and IC11 (64K × 8 wave RAM) Eight channels
CD-ROM decoder IC13, Sanyo LC8951, with IC14 and IC15 (16K × 8 buffer) Error correction for CD-ROM data
Back-up RAM IC16, MB8464A, 8K × 8 Held up by the cell BT on the main board
Audio Sub board: LC7883 and LC7881 D/A converters, µPC844 op-amps CD audio from the drive goes through the LC7883; PCM goes through the LC7881 and a low-pass filter. The two are mixed, filtered at 20 kHz and sent to the LINE OUT jacks
Clock 50 MHz crystal oscillator

Boards

[edit | edit source]

The unit has three boards and a drive unit. The export manual gives parts lists for the export boards and carries Sega's schematics and mount diagrams, which are drawn for the earlier main board 837-8015-01 and sub board 837-8046-01.[2][6]

Boards and drive units
Board Export assembly Earlier assembly What it carries
Main 837-8952 (PCB 171-6326A) 837-8015-01 Sub CPU, gate array, all RAM, boot ROM, CD-ROM decoder, PCM chip, back-up cell, LEDs
Sub 837-8953 (PCB 171-6327A) 837-8046-01 DC input, fuse, 5 V regulator, audio D/A converters and output stage, MIX and LINE OUT jacks
Connect 839-0534 (PCB 171-6328A) 837-8326 or 837-8327-01 The 60-pin edge connector to the console
Drive unit 610-5270 (Sony KSK-1200A) or 610-5270-10 (JVC ELM-135) Complete CD mechanism, servo and pickup

Console5 records the Sony KSK-1200A with a KSS-240A pickup and the JVC drive (PCB EMW10258 / ENN-335A-1) with an Optima-5S pickup. The two mechanisms share no parts.[6]

Power

[edit | edit source]

The Model 1 has its own external adaptor. Sega's accessories list for Europe gives 400-5122A and 400-5122B for 220 V mains and 400-5127 and 400-5127A for 240 V, all 10 V DC at 1.2 A.[5] On the sub board the DC input goes through fuse F1, a Pico II 2.5 A radial part, and diode D1 to IC6, a µPC2405HF 5 V regulator on a heat sink.[2][6]

Servicing

[edit | edit source]

Sega's PCB repair flow chart works at module level.[7] With no picture and no power, it blames the AC adaptor or the sub board. With a picture, it sends a missing CD-ROM screen to the main board or the Mega Drive, a tray that will not open or shut to the CD drive unit, no sound to the FFC cable between the main and sub boards, and a mixing fault to the plug cord or the Mega Drive. The drive unit is a complete assembly with a single Sega part number, and the manual gives no adjustment procedure for it.[4]

The electrolytic capacitors are the usual age fault: twelve on the export main board, ten of them surface-mount, and eighteen on the sub board.[2] See the Sega CD (Model 1) Capacitor Replacement Guide for the list, the Sega CD (Model 1) Troubleshooting Guide for fault finding and the Sega CD (Model 1) Maintenance Guide for strip-down and cleaning.

Things that are not faults

[edit | edit source]
  • No picture from the Mega-CD on its own. It has no video output.
  • No CD sound through the television with a Model 1 Mega Drive. The CD unit's sound comes out of its own LINE OUT jacks; to hear the console and the CD together, the Mega Drive's headphone output is cabled into the input jack on the back of the CD unit and the mixed sound is taken from the CD unit. A Model 2 console does not need the cable.[1]
  • Two mains adaptors. The add-on has its own by design.

Documentation

[edit | edit source]
[edit | edit source]
  • Sega's mount diagram for the main board 837-8015-01
    Sega's mount diagram for the main board 837-8015-01
  • Sega's mount diagram for the sub board 837-8046-01
    Sega's mount diagram for the sub board 837-8046-01
[edit | edit source]

References

[edit | edit source]
  1. ↑ 1.0 1.1 1.2 1.3 1.4 Sega CD—link(accessed 2026-10-01) Secondary source; the dates and prices are cited there to Sega's own Mega-CD page, Retro Gamer issue 153 and Computer and Video Games issue 138, p. 8.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 Sega Enterprises, Ltd., MEGA-CD Maintenance Manual (Export), August 1992, Rev. A, section 8, parts lists for main board 837-8952 (PDF pp. 94-96), sub board 837-8953 (pp. 97-98) and connect board 839-0534 (p. 99). See Sega CD Service Manual.
  3. ↑ 3.0 3.1 3.2 3.3 Sega Enterprises, MEGA-CD Maintenance Manual (Export), August 1992, Rev. A, section 1, block diagram (PDF p. 5, "MEGA-CD HARD MANUAL", Ver. 0.5, 2 July 1991). See Sega CD Service Manual.
  4. ↑ 4.0 4.1 Sega Enterprises, MEGA-CD Maintenance Manual (Export), August 1992, Rev. A, section 2-2 assembly lists (assembly 1006, PDF pp. 19-20), section 2-3 disassembly and assembly procedure (pp. 23-24) and section 3 spare parts list (p. 26). See Sega CD Service Manual.
  5. ↑ 5.0 5.1 Sega Enterprises, MEGA-CD Maintenance Manual (Export), August 1992, Rev. A, section 4, accessories list for Europe (PDF p. 28). See Sega CD Service Manual.
  6. ↑ 6.0 6.1 6.2 Sega CD v1—link(accessed 2026-10-01) Secondary source: IC lists and capacitor lists read off real boards, including the earlier Japanese boards and both drive PCBs.
  7. ↑ Sega Enterprises, MEGA-CD Maintenance Manual (Export), August 1992, Rev. A, section 5, PCB repair flow chart (PDF p. 30). See Sega CD Service Manual.
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