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Sega CD (Model 2)

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Revision as of 09:55, 1 October 2026 by Josh (talk | contribs) (Infobox photo; fix IC409 test pins (1, 12, 13, not 1-3) and focus pins; IC108/109 are PCM RAM, IC107 program RAM; IC201/202 are CD and PCM DACs; magnetic chuck, not spring clamp; mixing-jack direction; model numbers and history; page-cited refs)
Sega CD II / Mega-CD 2
A Model 2 Sega CD (right) attached to a Model 2 Genesis
Specifications
ManufacturerSega Enterprises, Ltd.
TypeCD-ROM add-on for the Mega Drive / Genesis
Released23 April 1993 (Japan)[1]
Intro priceUS$229 in North America, bundled with Sewer Shark[1]
CPU68000 at 12.5 MHz (sub CPU)[2]
Memory6 Mbit program, picture and sound RAM; 512 kbit PCM waveform RAM; 128 kbit CD-ROM cache; 64 kbit back-up RAM[2]
StorageTop-loading CD drive, 12 cm and 8 cm discs, average access 1.5 s[2]
DisplayNone; video is produced by the console
Sound8-channel stereo PCM at up to 32 kHz; 16-bit D/A converter with 8× oversampling digital filter[2]
PowerExternal AC adaptor, 10 V DC 1.2 A; 18 W[2][3]
Dimensions396 × 220 × 84 mm[2]
OS / Firmware1 Mbit boot ROM: CD game BIOS, CD player software, CD+G[2]
PredecessorSega CD (Model 1)
Model no.MK-4101 (USA), MK-4101-22 (Canada), MK-4180 and MK-4182 (Mega CD II)[3]

The Sega CD Model 2, sold as the Sega CD II in North America and the Mega-CD 2 elsewhere, is Sega's second CD-ROM add-on for the Mega Drive and Genesis. It replaced the Model 1's motorised front-loading tray with a top-loading lid opened by hand, sits beside the console instead of under it, and was designed to cost less to make.[1] To software it is the same machine: the same 68000 sub CPU at 12.5 MHz, the same memory and the same boot ROM functions.[2]

History

Sega released the Mega-CD 2 in Japan on 23 April 1993. It reached North America several months later at US$229, bundled with Sewer Shark.[1] Sega's parts list gives four model numbers: MK-4101 for the USA, MK-4101-22 for Canada (packed with Sewer Shark), and MK-4180 and MK-4182 for other markets (MK-4180 packed with Road Avenger).[3]

Specifications

From Sega's service manual.[2]

Sega CD II / Mega CD II specifications
Item Sega CD II Mega CD II
Power input (adaptor) AC 120 V, 60 Hz AC 230 or 240 V, 50 Hz
Power consumption 18 W
Operating environment 0 to 40 °C, 10 to 80 % RH, no condensation
CPU 68000 at 12.5 MHz
RAM 6 Mbit program, picture and sound data; 512 kbit PCM waveform; 128 kbit CD-ROM data cache; 64 kbit back-up
Boot ROM 1 Mbit: CD game BIOS, CD player software, CD+G
PCM Stereo, 8 channels, sampling frequency up to 32 kHz
D/A conversion 16-bit, 8× internal oversampling digital filter; PCM and CD sound mixing
Audio 20 Hz to 20 kHz; S/N over 80 dB at 1 kHz (line out); dynamic range over 90 dB
Back-up retention About one month
Discs 12 cm and 8 cm
Access time Average 1.5 s
Connections Two RCA line-out jacks; stereo mixing jack; AC adaptor jack

Power

The unit runs from its own adaptor, rated 10 V DC 1.2 A: Sega parts 400-5100B and 400-5100B-01 for 120 V mains, 400-5122C for 230 V, and 400-5127A and 400-5128A for 240 V.[3] The DC input goes from jack CN301 through fuse F301 (Pico II, 2.5 A) to IC301, a µPC2405HF 5 V regulator.[4] Sega's servicing flow charts check for 9 V at pins 1, 12 and 13 of IC409, the AN8388 servo driver, and 5 V at pins 10 and 37 of IC403.[5]

Boards

Two different main boards were made. Sega's manuals describe one, the board Console5 calls the Funai board; the other, 171-6528C, Console5 calls the Sony board.[6][7]

Model 2 main boards
Board Identification CD section
"Funai" board, Sega 837-9615 (Sega CD II, USA) or 837-9616 (Mega CD II, multi); later 837-10210, -10211, -10213 and -10214[4][8] Silkscreened BE2200G02 with a revision suffix (A02, B02, C02 or C22)[6] IC401 CXD1167Q signal processor, IC402 CXA1081M RF amplifier, IC403 CXA1082BQ servo signal processor, IC404 µPD75006 mechanism controller, IC409 AN8388 servo driver[4]
"Sony" board, 171-6528C Boot ROM MPR-15764-T at IC111[7] IC401 CXD2500BQ, IC402 CXP5084; the drive's own PCB carries the servo[7]

On the Funai board, units from serial number T30282001 have larger chip parts (2.0 × 1.25 mm instead of 1.6 × 0.8 mm), a changed board pattern, IC001 and IC002 renumbered IC951 and IC952, and no PCM board 837-9798 at IC110.[8] On earlier boards IC001 and IC002 are on a small add-on board, BE2200F01003, wired to the top of the main board.[6]

Main ICs, Funai board[4][9]
Position Part Function
IC101 315-5632, custom chip MCE3 Gate array
IC102, IC103 TC511664BJ-80 or µPD421664 Word RAM
IC104, IC105 CXK5864BM-70 CD-ROM buffer RAM
IC106 LC89515 CD-ROM decoder
IC107 µPD424270, HM514270AJ, M5M44270AJ or MN414270SJ Program RAM, 4 Mbit
IC108, IC109 LH5P832N-10 or TC51832FL-10 PCM waveform RAM
IC110 315-5476A, RF5C164A PCM sound
IC111 EPR-15511 or MPR-15511A (Sega CD II); EPR-15512 or MPR-15512A (Mega CD II) Boot ROM
IC112 MB8464A-10LL Back-up RAM
IC113 MC68HC000FN12, HD68HC000CP-12 or TMP68HC000T-12 Sub CPU
IC114 MB3790 Battery back-up
IC201 LC7883KM CD audio D/A converter
IC202 LC78815M PCM D/A converter
IC203 to IC205 NJM3403AM, NJM3404AM Op-amps
IC301 µPC2405HF 5 V regulator

Clocks are X101, a 50.000 MHz oscillator; X401, a 16.9344 MHz crystal; and X702, a 4.19 MHz ceramic resonator. The connector to the console, CN101, is a 60-pin edge connector.[4]

Drive units

The supplement lists two drive units for the Funai board, told apart by the label on the mechanism: 610-5608, labelled KSS-210A, and 610-5603, labelled SOHOT4. Ten resistors and three capacitors around the drive differ between them, C412 among them, and the tracking gain adjustment value is 1 kHz/0 dB for 610-5608 and 800 Hz/0 dB for 610-5603.[8] The Sony board uses a KSK-1310A (KSM2401AAN mechanism, KSS-240A pickup) or an Optima 6S drive.[7]

Servicing

Sega's guides for servicing are flowcharts for the focus, tracking, disc and feed circuits, each starting with the 9 V check at IC409. Among the figures they give: laser power 90 to 120 µW; an RF waveform of about 1.5 Vp-p at IC402 pin 2 (TP-RF); about 7 V focus drive between IC409 pins 7 and 8; and about 3 V focus error output between IC403 pins 7 and 5.[5] Setting the door switch SW401 from off to on should light the laser for about two seconds and move the lens up and down.[5]

The drive has three adjustments: VR403 sets the VCO to 4.320 ± 0.05 MHz at TP-PLCK, VR401 sets EF balance and VR402 sets tracking gain. The procedure needs Sega's adjustment jig on CN403, a Sony TYPE-4 test disc, a frequency counter, an oscilloscope, an audio generator and two voltmeters.[10]

See the Sega CD (Model 2) Troubleshooting Guide for fault finding, the Sega CD (Model 2) Maintenance Guide for strip-down and cleaning, and the Sega CD (Model 2) Capacitor Replacement Guide for the capacitor lists by board.

Things that are not faults

  • No drive belt or tray motor. The lid is opened by hand.
  • Its own adaptor. The add-on is powered separately from the console.
  • No video of its own. The picture comes from the console.
  • The mixing jack. It is for the original Mega Drive and Genesis, whose sound is cabled into it; the Model 2 console does not need the cable.[11][1]
  • Saves lost after about a month without power. Sega's back-up retention figure is about one month.[2]

Documentation

  • An early Funai main board, with the add-on board for IC001 and IC002 wired on
    An early Funai main board, with the add-on board for IC001 and IC002 wired on
  • A main board with boot ROM MPR-15764-T, which Console5 lists on the 171-6528C board
    A main board with boot ROM MPR-15764-T, which Console5 lists on the 171-6528C board
  • Sega's circuit board diagram for the main board
    Sega's circuit board diagram for the main board

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 Sega CD—link(accessed 2026-10-01) Secondary source; the Japanese date is cited there to Sega's own Mega-CD 2 page and the North American price to GamePro issue 52.
  2. ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 Sega Enterprises, Ltd., Service Manual, Sega CD II / Mega CD II, No. 002, August 1993, section 1, specifications, p. 2. See Sega CD 2 / Mega CD 2 - Service Manual.
  3. ↑ 3.0 3.1 3.2 3.3 Sega Enterprises, Ltd., Service Manual, Sega CD II / Mega CD II, No. 002, August 1993, section 13-4, accessories and package list, p. 42. See Sega CD 2 / Mega CD 2 - Service Manual.
  4. ↑ 4.0 4.1 4.2 4.3 4.4 Sega Enterprises, Ltd., Service Manual, Sega CD II / Mega CD II, No. 002, August 1993, section 13-3, electrical parts list, pp. 39-42. See Sega CD 2 / Mega CD 2 - Service Manual.
  5. ↑ 5.0 5.1 5.2 Sega Enterprises, Ltd., Service Manual, Sega CD II / Mega CD II, No. 002, August 1993, section 8, guides for servicing: overall chart (p. 11), focus (p. 12), tracking (p. 12), disc (p. 13) and feed (p. 14) circuit flowcharts. See Sega CD 2 / Mega CD 2 - Service Manual.
  6. ↑ 6.0 6.1 6.2 Sega CD v2: Funai—link(accessed 2026-10-01) Secondary source; IC and capacitor lists read off real boards.
  7. ↑ 7.0 7.1 7.2 7.3 Sega CD v2: Sony—link(accessed 2026-10-01) Secondary source; IC and capacitor lists read off real boards.
  8. ↑ 8.0 8.1 8.2 Sega Enterprises, Ltd., Service Manual Supplement, Sega CD II / Mega CD II, No. 002-2, June 1994. See Sega CD 2 / Mega CD 2 - Service Manual Supplement.
  9. ↑ Sega Enterprises, Ltd., Service Manual, Sega CD II / Mega CD II, No. 002, August 1993, section 9, block diagram, p. 15. See Sega CD 2 / Mega CD 2 - Service Manual.
  10. ↑ Sega Enterprises, Ltd., Service Manual, Sega CD II / Mega CD II, No. 002, August 1993, section 4, CD drive adjustment, pp. 6-7. See Sega CD 2 / Mega CD 2 - Service Manual.
  11. ↑ Sega Enterprises, Ltd., Service Manual, Sega CD II / Mega CD II, No. 002, August 1993, section 2, identifying parts and accessories, p. 3. See Sega CD 2 / Mega CD 2 - Service Manual.
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