Sega Master System II General Maintenance
The Sega Master System II is the cost-reduced Master System of 1990. Sega removed the Sega Card slot, the reset button, the power light and the expansion port, and in most regions the A/V output, leaving RF only; the French version has A/V output and no RF modulator.[1] The PAL board (171-5922A) has nine ICs, a single +5 V rail from a 7805 regulator, and fourteen electrolytic capacitors. The case measures 256 × 172 × 81.5 mm and the console weighs 790 g.[2][3]
For fault-finding see the Sega Master System II Troubleshooting Guide. Capacitor values for each board are in the Sega Master System II Capacitor Replacement Guide.
Identify the board
[edit | edit source]Sega's April 1991 manual covers the PAL board 171-5922A ("IC BD M4JR PAL") and the French RGB board 171-5926A ("PC BD M4 JR VA1").[3][4] Its parts-location drawings give a separate assembly number for each regional build:[5]
| Drawing title | Assembly | Sub-assembly | PDF page |
|---|---|---|---|
| IC BD M4JR PAL-B (VV) | 837-7370 | 610-5145 | 21 |
| IC BD M4JR PAL-G | 837-7367 | 610-5152 | 22 |
| IC BD M4JR PAL-B (VE) | 837-7371 | 610-5146 | 23 |
| IC BD M4JR PAL-D | 837-7559 | 610-5154 | 24 |
| IC BD M4JR PAL-I | 837-7369 | 610-5130 | 25 |
| IC BD M4JR RGB | 837-7560 | 610-5147 | 26 |
The PAL boards use a 53.203424 MHz oscillator module, gate array 315-5237 at IC4 and a CXA1145P video encoder at IC9. The RGB board uses a 10.738635 MHz crystal and a DIN A/V socket (CN5); its parts list gives IC4 as 315-5216, with "315-5237" written beside it by hand in the scanned copy.[3][4] Later boards that the manual does not cover include 171-6395A ("IC BD M4Jr. PAL 2M", with an MB3514 encoder and the BIOS at IC10) and 837-7275 ("IC BD M4Jr. VA1"); Console5 lists their parts.[6]
Safety
[edit | edit source]The console runs from an external 9 V DC adaptor and has no mains wiring inside it.[7] The adaptor is a mains transformer unit. If you open one, unplug it first and treat the primary side as live until you have measured it.
Use an earthed wrist strap when handling the board. The VDP (IC5, 315-5246) and the gate array (IC4) are Sega custom parts.[3]
Disassembly
[edit | edit source]Sega's manual has no disassembly procedure.
- Unplug the adaptor and any controllers.
- Turn the console over, remove the case screws and lift away the top case.
- Remove the top shield (250-5185). The bottom shield is 250-5186.[3]
- Lift the board out, noting how the DC jack (CN4) and the controller sockets (CN2, CN3) sit in the case.
The 7805 regulator (IC8) is screwed to a heatsink with thermal compound; Sega lists the compound (601-0076) in both parts lists and the screw (M3 × 8, 029-0214) in the RGB list.[3][4] Refit it properly on reassembly. Sega's fault list for a dead console includes "heat sink attachment faulty" alongside a failed 7805 and a faulty power switch.[7]
Cleaning
[edit | edit source]Wash the case halves in warm soapy water and dry them fully before refitting the board. For yellowed plastic see Retrobrite.
Clean the controller sockets (CN2, CN3) and the cartridge edge connector (CN1, 50-pin) with isopropyl alcohol or contact cleaner. Sega's fault lists name dirty or broken connector pins, poor soldering and cracked tracks at these connectors as causes of no picture, a monochrome picture and controls that do not respond.[7] Clean the DC jack (CN4, Sega part 212-5004) and check its solder joints if the console cuts out when the plug is moved.[3]
The pause button is a tactile switch (509-5207 or 510-5019).[3] Sega's listed faults for it are poor soldering, a cut track, a short, and a switch blade that is not parallel with the board.[7]
Board inspection
[edit | edit source]Look for:
- domed, leaking or stained electrolytic capacitors (see Capacitor Failure Symptoms);
- cracked joints at CN1, CN2, CN3, CN4 and the shield mounting points;
- a loose 7805 or dried compound under it;
- damaged parts in the controller input filtering: EMI filters EM11–EM18 and EM21–EM28 and the 330 Ω resistors R5–R8. Sega's controller fault list names both.[3][7]
Capacitors
[edit | edit source]On the PAL board 171-5922A the electrolytics are C18, C31, C32, C38, C41, C42, C43 and C44 in the main C series, plus six 10 µF bypass capacitors labelled CE1–CE6, fourteen in all. The parts marked CP (CP1–CP13) are 0.022 µF ceramics (Sega part 151-0170), not electrolytics.[3] Console5's list for this board gives CP as 10 µF 16 V; Sega's parts list and its parts-location drawings both mark them 0.022 µF.[6][5] Values change between boards: C32 is 10 µF 16 V on 171-5922A and 330 µF 16 V on 171-6395A.[3][6] Identify the board before ordering parts. Full lists are in the Sega Master System II Capacitor Replacement Guide.
Sega's PAL drawings carry the note "Land near CXA1145 is the positive side".[5]
Power supply
[edit | edit source]| Part | Rating | Market |
|---|---|---|
| 400-5126 | AC 220 V in, DC 9 V 0.5 A | Europe |
| 400-5129 | AC 240 V in, DC 9 V 0.5 A | UK |
| 400-5130 | AC 240 V in, DC 9 V 0.5 A | Australia |
| 400-5048Y | AC 220 V in, DC 9 V 1 A | France (RGB version) |
The adaptors are from the PAL and RGB parts lists.[3][4] The adaptor table on p. 1 of the same manual gives other numbers for some markets (400-5050 for Australia and New Zealand, 400-5115 for America).[2]
Measure the supply with the console connected and running. Sega's test is DC 9 V at the input of IC8 and DC 5 V at its output.[7] A replacement adaptor must match the original's voltage and polarity and be rated for at least its current.
Test points
[edit | edit source]These are Sega's own checks, from the repair procedures in the April 1991 manual.[7]
| Point | Sega's figure | Notes |
|---|---|---|
| IC8 input | DC 9 V | From the adaptor |
| IC8 output | DC 5 V (Vcc) | Feeds every IC |
| Test point JR | 0 to 3.6 V, rising slowly at power-on | Reset; Sega names C18 and R4 |
| IC4 pin 41 | 10.738635 MHz ±100 Hz, about 6 Vp-p | NTSC figure, matching the RGB board's crystal. For this check Sega's fault list names "OSC (53M)", the 53.203424 MHz oscillator of the PAL boards[3] |
| IC5 pin 33 | 3.579545 MHz ±30 Hz | CPU clock as printed by Sega (the NTSC figure). A PAL board divides 53.2034 MHz by 15 to give 3.546893 MHz[8] |
| IC4 pin 42 | 4.43361875 MHz ±30 Hz | PAL colour subcarrier |
| IC5 pin 15 | Audio, up to 300 mVp-p, 20 Hz–20 kHz | Sound output from the VDP |
| RF modulator pin 3 | Video present | Then IC9 pins 19 and 20 (video out) and pins 1–4 (RGB in) |
After maintenance
[edit | edit source]- Power up with no cartridge fitted and check that a picture appears.
- Check the 5 V rail at IC8.
- Test both controller ports in every direction and with both buttons.
- Insert and remove a known-good cartridge several times and check that it starts each time.
- Check the picture and sound through the TV.
References
[edit | edit source]- ↑ Master System, Wikipedia, sections on the Master System II and its hardware (accessed 2026-10-01).
- ↑ 2.0 2.1 Sega Master System II Service Manual, Sega Enterprises, April 1991, pp. 1–2 (PDF pp. 3–4): model numbers by territory, AC adaptor specifications, dimensions and weight, and electrical specifications. See Sega Master System II Service Manual (1991).
- ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 3.11 3.12 Sega Master System II Service Manual, April 1991, Parts List for PAL Version, pp. 19–21 (PDF pp. 13–15), board 171-5922A.
- ↑ 4.0 4.1 4.2 4.3 Sega Master System II Service Manual, April 1991, Parts List for RGB Version, pp. 25–26 (PDF pp. 16–17), board 171-5926A.
- ↑ 5.0 5.1 5.2 Sega Master System II Service Manual, April 1991, PCB parts-location diagrams, pp. 14–18 and 24 (PDF pp. 21–26), read from the drawing title blocks.
- ↑ 6.0 6.1 6.2 Sega Master System, Console5 TechWiki (accessed 2026-10-01): chip lists and capacitor lists for 171-5922A, 171-6395A and 837-7275.
- ↑ 7.0 7.1 7.2 7.3 7.4 7.5 7.6 Sega Master System II Service Manual, April 1991, Repair Procedures, pp. 3–8 (PDF pp. 5–10): troubleshooting flowchart, main-unit test procedures, symptoms by IC, no-sound, no-picture and controller fault lists.
- ↑ Clock Rate, SMS Power! (accessed 2026-10-01): PAL master clock 53.2034 MHz divided by 15 gives 3546893 Hz; NTSC 53.6931 MHz gives 3579540 Hz.