Sega CD (Model 2) Troubleshooting Guide
Fault finding for the Sega CD Model 2 (Sega CD II, Mega-CD 2). Sega's service manual No. 002 gives a set of servicing flowcharts with test points and waveforms, and the sections below follow them.[1] The test points apply to the board Sega's manuals cover, which Console5 calls the Funai board (silkscreened BE2200G02); the other board, 171-6528C, uses a different CD section.[2][3]
Identify the board
[edit | edit source]| Board | How to tell | CD section |
|---|---|---|
| Funai: Sega 837-9615 (Sega CD II) or 837-9616 (Mega CD II); later 837-10210, -10211, -10213, -10214 | Silkscreened BE2200G02 with suffix A02, B02, C02 or C22[2] | IC401 CXD1167Q, IC402 CXA1081M, IC403 CXA1082BQ, IC404 µPD75006, IC409 AN8388[4] |
| Sony: 171-6528C | Boot ROM MPR-15764-T at IC111[3] | IC401 CXD2500BQ, IC402 CXP5084[3] |
From serial number T30282001 the Funai board has larger chip parts and a changed pattern, IC001 and IC002 become IC951 and IC952, and the PCM board 837-9798 is not used. The supplement also adds a second drive unit, 610-5603 (labelled SOHOT4), alongside 610-5608 (labelled KSS-210A), with different component values around the drive and a different tracking gain setting.[5]
Power
[edit | edit source]| Test point | Expected | Notes |
|---|---|---|
| DC input at CN301 | 10 V DC from the adaptor | Adaptor rated 1.2 A: Sega parts 400-5100B and 400-5100B-01 (120 V), 400-5122C (230 V), 400-5127A and 400-5128A (240 V)[6] |
| Fuse F301 | Continuity | Pico II, 2.5 A.[4] If it has blown, find the cause before replacing it |
| IC301 output | 5 V | µPC2405HF regulator[4] |
| IC403 pins 10 and 37 | 5 V | Checked at the start of Sega's feed flowchart[1] |
| IC409 pins 1, 12 and 13 | 9 V | Checked at the start of every one of Sega's focus, tracking, disc and feed flowcharts; if absent, check the power circuit[1] |
Sega's overall servicing chart
[edit | edit source]Work down the list. Sega's answer to a "no" at steps 1 to 5 is to check the control circuits.[1]
- Does the unit power on?
- Does the LED flash normally?
- Is the Sega CD II / Mega CD II introduction picture normal?
- Does the control picture appear when Start is pressed?
- Does the cursor move?
- Does the counter read "00:00" when the CD door is closed? If not, go to the laser and focus checks below.
- Is the TOC read? If not: if the disc rotates, check that the tracking loop engages at IC403 pin 11, then look for an RF waveform of about 1.5 Vp-p at IC402 pin 2 (TP-RF). No RF means checking IC402 and the pickup; RF present means going to the disc circuit flowchart.
- Can the first track of a test CD be played? If not, check the EF balance adjustment, then the tracking, feed and disc flowcharts, then the pickup: a dirty lens, or laser power outside 90 to 120 µW.
- Is the RF at TP-RF normal, and can each track be found? If not, the same chain applies.
- Is there sound? If not, check the audio circuit.
Laser and focus checks
[edit | edit source]When the counter does not read "00:00", Sega's chart works through what happens when the door switch SW401 is set from off to on:[1]
| Check | Expected | If not |
|---|---|---|
| Does the pickup lens move up and down? | Yes | If IC404 pin 44 is at 0 V, go to the focus circuit flowchart; if not, go to the feed circuit flowchart |
| Is the laser lit for about 2 seconds? | Yes; laser power 90 to 120 µW | If IC404 pin 29 goes from 5 V to 0 V for about 2 seconds, check the circuit around Q401, the 8-pin cable and the pickup. If not, and IC404 pin 44 goes from 5 V to 0 V for about 2 seconds, check the connection at IC402 pin 29; otherwise IC404 is faulty |
| Is focus held for about 2 seconds, seen as lens movement? | Yes: go to the disc circuit flowchart | Go to the focus circuit flowchart |
TOC read-in sequence
[edit | edit source]Sega's TOC read-in flowchart gives the order of events after power-on.[7] Where it stops shows which flowchart to use.
- Power on.
- The pickup moves to the inner edge.
- SW501, the pickup position switch, turns on.
- Laser on.
- Focus search.
- Focus servo on.
- The disc starts to turn.
- Tracking servo on.
- Disc servo on.
- The TOC is read.
Focus circuit
[edit | edit source]| Check | Expected | If not |
|---|---|---|
| IC409 pins 1, 12, 13 | 9 V | Check the power circuit |
| With the top cover off, set SW401 on: does the lens move up and down? | Yes | Check the focus drive between IC409 pins 7 and 8 |
| Focus drive (FD) between IC409 pins 7 and 8 | Ramp of about 7 V | Check the focus error output between IC403 pins 7 and 5; if that is present, check the path from IC403 to IC409 |
| Focus error output (FEO) between IC403 pins 7 and 5 | Ramp of about 3 V | IC403 faulty |
| Waveform at TP-X1 as SW401 goes from off to on | About 4 Vp-p, about 0.5 ms | Check the pickup (dirty lens, laser output) and the RF amplifier IC402; if present, check focus circuit IC403 |
Tracking circuit
[edit | edit source]| Check | Expected | If not |
|---|---|---|
| IC409 pins 1, 12, 13 | 9 V | Check the power circuit |
| Is the TOC read? | Yes: check that all tracks can be searched, then go to the feed flowchart | |
| Waveform at TP-X | About 2 V, changing when the servo turns on | Check the pickup (dirty lens, laser power 90 to 120 µW) and the tracking circuit |
| Waveform at IC403 as the servo turns on | Present | Check the tracking circuit, IC403 |
Disc circuit
[edit | edit source]| Check | Expected | If not |
|---|---|---|
| IC409 pins 1, 12, 13 | 9 V | Check the power circuit |
| Disc stopped in stop mode | Yes | If IC403 pin 39 is at 2.5 V, check IC409; otherwise check IC401 and IC403 |
| Disc turns 1 to 2 seconds after SW401 goes from off to on | Yes | Look for +3 V between IC409 pins 3 and 4. If present, check the disc motor M501 and its connections; if not, check the drive waveform at IC403 pin 39 and its path to IC409 pin 23 |
| Disc stops immediately when Stop is pressed | Yes | Look for −3 V between IC409 pins 3 and 4. If present, check M501; if not, check whether IC403 pin 39 rises by 1 V, then the path to IC409 pin 23 and IC409 |
Feed circuit
[edit | edit source]| Check | Expected | If not |
|---|---|---|
| IC403 pins 10 and 37; IC409 pins 1, 12, 13 | 5 V; 9 V | Check the power circuit |
| TOC not read, pickup not at the inner edge | 4 V between IC409 pins 5 and 6 | If present, check the feed motor and its connections |
| Pickup at the inner edge | IC403 pin 16 (SSTOP) goes from 5 V to 0 V when the pickup switch SW501 turns on | Check the connection between SW501 and IC404 |
| Tracks cannot be searched | Search waveform at IC403 pin 14, then between IC409 pins 5 and 6 | No waveform at IC403: check the feed circuit (IC403). None at IC409: check the path from IC403 pin 14 to IC409 pin 21. Both present: check the feed motor |
Digital section
[edit | edit source]| 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 or equivalent | 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 | 68HC000 | Sub CPU, 12.5 MHz |
| 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: X101 is a 50.000 MHz oscillator, X401 a 16.9344 MHz crystal and X702 a 4.19 MHz ceramic resonator.[4]
CD interface
[edit | edit source]The signals between the CD section and the rest of the board, from Sega's CD interface table:[9]
| Signal | Direction | From | Function |
|---|---|---|---|
| C2PO | Out | IC401 | Error flag; high when data correction is disabled |
| BCLK, SDATA, LRCK | Out | IC401 | Bit clock, serial data, left/right channel clock |
| 16MHz | Out | IC401 | 16.9344 MHz |
| WFCK | Out | IC401 | Frame clock |
| EXCK | In | IC401 | Sub-code read clock |
| SBSO, SCOR | Out | IC401 | Sub-code data and sync |
| L-MUTE | Out | IC404 | Low while music plays, high otherwise |
| IRQ | Out | IC404 | Interrupt request |
| COCK | Out | IC404 | CD mechanism control communications clock |
| HOCK | In | IC404 | Host communications clock |
| DB0 to DB3 | In/out | IC404 | Data bus |
| RESET | In | IC404 | Resets the CD hardware |
Audio
[edit | edit source]Sega's block diagram shows CD audio going through IC201 (LC7883) and PCM sound through IC202 (LC78815M), then op-amps IC203 to IC205. The mixed sound goes to the RCA line-out jacks CN202 and, through CN101, to the console; the stereo mini jack CN201 takes sound in from an original Mega Drive or Genesis.[8][10]
| Symptom | Probable cause | Action |
|---|---|---|
| No CD audio, RF waveform normal | CD audio path: IC201, op-amps | Check IC201 and the op-amp stages; check the electrolytics in the audio circuits |
| PCM effects missing, CD audio present | PCM path: IC110, IC108/IC109, IC202 | Check IC202 and its circuit, then IC110 |
| Weak, noisy or one channel | Electrolytics in the audio stages | Recap: see Sega CD (Model 2) Capacitor Replacement Guide |
| No console sound with a Model 1 Mega Drive | Mixing cable missing | Cable the console's headphone output to the mixing jack CN201 |
Sega's audio specification: 20 Hz to 20 kHz, S/N over 80 dB at 1 kHz at the line out, dynamic range over 90 dB.[11]
Saves are lost
[edit | edit source]Sega's figure for back-up retention is about one month.[11] The back-up RAM is IC112, held up by the rechargeable cell BT101 (ML2016-HS1) through IC114 (MB3790).[4][8] A unit that loses saves within days needs a new cell; see Sega CD (Model 2) Maintenance Guide.
Things that are not faults
[edit | edit source]- Its own adaptor: the add-on is powered separately.[6]
- No picture of its own: the picture comes from the console.
- No belt or tray motor: the lid is opened by hand.
- Saves lost after about a month without power.[11]
Related pages
[edit | edit source]- Sega CD (Model 2)
- Sega CD (Model 2) Maintenance Guide
- Sega CD (Model 2) Capacitor Replacement Guide
- Sega CD (Model 1) Troubleshooting Guide
- Sega Mega Drive / Genesis (Model 2) Troubleshooting Guide
- Capacitor Failure Symptoms
References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 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 and tracking circuit flowcharts (p. 12), disc circuit flowchart (p. 13) and feed circuit flowchart (p. 14). See Sega CD 2 / Mega CD 2 - Service Manual.
- ↑ 2.0 2.1 Sega CD v2: Funai—link(accessed 2026-10-01) Secondary source.
- ↑ 3.0 3.1 3.2 Sega CD v2: Sony—link(accessed 2026-10-01) Secondary source. Lists the 171-6528C board's CD section as IC401 CXD2500BQ and IC402 CXP5084, with a KSK-1310A or Optima 6S drive.
- ↑ 4.0 4.1 4.2 4.3 4.4 4.5 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.
- ↑ 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.
- ↑ 6.0 6.1 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.
- ↑ Sega Enterprises, Ltd., Service Manual, Sega CD II / Mega CD II, No. 002, August 1993, section 7, TOC read-in flowchart, p. 10. See Sega CD 2 / Mega CD 2 - Service Manual.
- ↑ 8.0 8.1 8.2 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.
- ↑ Sega Enterprises, Ltd., Service Manual, Sega CD II / Mega CD II, No. 002, August 1993, section 5-2, description of CD interface, p. 9. See Sega CD 2 / Mega CD 2 - Service Manual.
- ↑ 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.
- ↑ 11.0 11.1 11.2 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.