Jump to content

Sega CD (Model 2) Maintenance Guide

From RetroTechCollection
An early Sega CD Model 2 main board, with the add-on board carrying IC001 and IC002 wired on

Routine care for the Sega CD Model 2, the top-loading add-on sold as the Sega CD II in North America and the Mega-CD 2 elsewhere. Sega's service manual No. 002 and its supplement No. 002-2 are hosted as Sega CD 2 / Mega CD 2 - Service Manual and Sega CD 2 / Mega CD 2 - Service Manual Supplement.

Two main boards exist. Sega's manuals cover the one Console5 calls the Funai board, silkscreened BE2200G02 with a revision suffix; the other, 171-6528C, Console5 calls the Sony board.[1][2] Designators and test points below are for the Funai board unless stated.

Power

[edit | edit source]

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. Power consumption is 18 W.[3] There is no mains voltage inside the unit; unplug the adaptor before opening it.

Power path and supply checks, Funai board
Point Part Expected
DC input Jack CN301 10 V from the adaptor[4]
Fuse F301, Pico II 2.5 A Continuity[4]
5 V logic IC301, µPC2405HF regulator 5 V; Sega's feed flowchart checks 5 V at IC403 pins 10 and 37[4][5]
9 V servo driver supply IC409, AN8388 9 V at pins 1, 12 and 13; every one of Sega's focus, tracking, disc and feed flowcharts starts with this check[5]

Disassembly

[edit | edit source]

Sega's procedures:[6]

  1. Chuck disk assembly: press the door knob to open the door and release the three stoppers holding the chuck disk assembly. On reassembly, align the recesses in the chuck holder with the stoppers. The chuck disk assembly comes apart into the connector plate, magnet, chuck holder and chuck disk once its screw and two stoppers are released.
  2. Top case: turn the unit over and remove six screws from the bottom. Do not remove the bottom case with the unit upside down; turn it the right way up and lift off the top case.
  3. Door: with the top case off, open the door, remove the blind sheet on the right and the door spring, turn the top case over, remove two screws and the oil damper, then push the door mounting in the direction of the arrows to release the bosses.
  4. CD drive unit: with the top case off, disconnect the three connectors and lift out the drive unit.
  5. Circuit board assembly: with the top case off, remove the five screws holding the shield plate, disconnect the three connectors from the CD drive unit and remove the two screws holding the board.

Cleaning

[edit | edit source]
  • Case: a damp cloth with mild detergent. For yellowed plastic see Retrobrite.
  • Inside: dry air or a soft anti-static brush over the board, drive and connectors; isopropyl alcohol on a lint-free cloth for grime. Do not soak the board.
  • Lens: a swab lightly dampened with isopropyl alcohol, wiped gently without pressure.
  • Edge connector CN101 and the console's expansion port: isopropyl alcohol, dried fully before power is applied.

The drive

[edit | edit source]

The Model 2 has no motorised tray and no drive belt; the door is opened by hand and the disc is held by a magnetic chuck.[6] The supplement lists two drive units for the Funai board, told apart by the label on the mechanism: 610-5608 (KSS-210A) and 610-5603 (SOHOT4). Ten resistors and three capacitors around the drive differ between them, including C412, and so does the tracking gain adjustment value.[7] Sony boards use a KSK-1310A or an Optima 6S drive.[2]

Drive adjustments

[edit | edit source]

The three trimmers are not laser power controls. Sega's procedure needs a frequency counter, an oscilloscope of 20 MHz or more, Sega's MEGA-CD II (F) CD ADJ. JIG on CN403, an audio generator, two voltmeters and a Sony TYPE-4 test disc. The jig's TEST button steps through the test modes; test mode 1 keeps the laser lit for a power check.[8]

CD drive adjustments[8]
Trimmer Adjusts Test point and mode Target If wrong
VR403 VCO TP-PLCK, with C410 shorted or TP-D grounded 4.320 ± 0.05 MHz Slow track search, or no play at all
VR401 EF balance TP-X, test mode 2 Peaks A and B of the waveform equal Poor play of dirty or scratched discs; track search fails
VR402 Tracking gain TP-X and TP-Y, test mode 3, 1.0 kHz 0.15 Vrms injected The two voltmeters read the same Too low: sensitive to shocks. Too high: poor play of dirty or scratched discs

On units with drive 610-5603 the tracking gain value is 800 Hz/0 dB instead of 1 kHz/0 dB.[7] Sega's laser power check is 90 to 120 µW, measured with a laser power meter; none of the three adjustments sets laser power.[5]

After fitting a replacement drive

[edit | edit source]

Sega's procedure:[9]

  1. Separate the unit from the Genesis or Mega Drive and unplug the adaptor.
  2. Replace the CD drive unit.
  3. Connect the adaptor and the console, and turn the door-close switch SW401 on by hand to power up. The laser should light for about two seconds and the lens should move up and down. Sega's caution: it is dangerous to look straight at a laser beam; do not bring your eyes close to it.
  4. Adjust EF balance (VR401), then tracking gain (VR402).
  5. Check for an RF waveform of about 1.5 Vp-p at IC402 pin 2 (TP-RF).

Capacitors

[edit | edit source]

The electrolytics, by board, are listed on the Sega CD (Model 2) Capacitor Replacement Guide: 47 on the Funai A02/B02/C02 board according to Sega's parts list, with C412's value depending on the drive.[4][7] On the Sony board the 10 µF parts are 50 V.[2] Fit 105 °C parts of the same value and at least the same voltage rating. Capacitor Failure Symptoms describes the signs of failure, and Battery Explosion, Capacitor or Corrosion Damage covers cleaning up after a leak.

Connectors

[edit | edit source]
  • CN101, the 60-pin edge connector to the console.[4]
  • CN301, the DC jack, whose solder joints carry the strain of the plug.
  • The three connectors between the main board and the drive.
  • CN201, the stereo mini jack for mixing, and CN202, the two RCA line-out jacks.[4] Sega labels the mixing jack for the original Mega Drive and Genesis.[10]

Clean with isopropyl alcohol and reseat. Reflow cracked joints.

Back-up memory

[edit | edit source]

Saves are held in IC112, an MB8464A-10LL, backed by the ML2016-HS1 cell BT101 and the MB3790 at IC114.[4][11] The ML2016 is a rechargeable cell.[12] Sega's figure for back-up retention is about one month, so saves lost after a long period unplugged are expected.[3] Replace a cell that no longer holds saves with the same rechargeable type, and check the board around it for corrosion. See Battery Refurbishment.

Storage

[edit | edit source]

Sega's operating range is 0 to 40 °C at 10 to 80 % relative humidity, without condensation.[3] Store the unit somewhere dry.

[edit | edit source]

References

[edit | edit source]
  1. ↑ Sega CD v2: Funai—link(accessed 2026-10-01) Secondary source.
  2. ↑ 2.0 2.1 2.2 Sega CD v2: Sony—link(accessed 2026-10-01) Secondary source.
  3. ↑ 3.0 3.1 3.2 Sega Enterprises, Ltd., Service Manual, Sega CD II / Mega CD II, No. 002, August 1993, section 1, specifications (p. 2), and 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 4.5 4.6 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, pp. 11-14. See Sega CD 2 / Mega CD 2 - Service Manual.
  6. ↑ 6.0 6.1 Sega Enterprises, Ltd., Service Manual, Sega CD II / Mega CD II, No. 002, August 1993, section 3, disassembly, pp. 4-5. See Sega CD 2 / Mega CD 2 - Service Manual.
  7. ↑ 7.0 7.1 7.2 Sega Enterprises, Ltd., Service Manual Supplement, Sega CD II / Mega CD II, No. 002-2, June 1994, p. 2. See Sega CD 2 / Mega CD 2 - Service Manual Supplement.
  8. ↑ 8.0 8.1 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.
  9. ↑ Sega Enterprises, Ltd., Service Manual, Sega CD II / Mega CD II, No. 002, August 1993, section 6, CD drive unit replacement procedure, p. 9. 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 2, identifying parts, p. 3. 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 9, block diagram, p. 15. See Sega CD 2 / Mega CD 2 - Service Manual.
  12. ↑ Coin Type Lithium Manganese Dioxide Rechargeable Batteries (ML), Maxell—link(accessed 2026-10-01)
Retrieved from "https://wiki.retrotechcollection.com/index.php?title=Sega_CD_(Model_2)_Maintenance_Guide&oldid=24306"