SEGA Master System II

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Master System II
SEGA Master System II
Master System II PCB M2
171-6395A/171-5922A
Master System II PCB
171-5926-A

Models and Specifications[edit | edit source]

Region Model Standard System
America MK-3006 NTSC M
Canada MK-3006-22 PAL B (VV)
Australia MK-3006-03 PAL B (VE)
New Zealand MK-3006 PAL D
China MK-3006-15 PAL G
Germany MK-3006-18 PAL G
France MK-3006-09 SECAM RGB

Board Revisions[edit | edit source]

Board Revision Part Number Standard Notes
IC BD M4Jr. VA1 (837-7275) 171-5926-A NTSC -
IC BD M4Jr. PAL 171-5922A PAL -
IC BD M4Jr. PAL 2M 171-6395A PAL -
IC BD M4Jr. VA1 (837-7275 RGB) 171-5926-A SECAM There is no RF modulator or composite video signal on this board (it outputs an RGB video signal only).

General Troubleshooting[edit | edit source]

Troubleshooting IC8[edit | edit source]

IC8 delivers the main +5V DC reference voltage (also referred to as VCC) for the whole board.
So yeah, we better make sure it works flawlessly 😄

Procedure[edit | edit source]

Steps
  1. Measure the input voltage VI. Voltage must be ≈ +8.3V DC[note 1] on this pin.
  2. Measure the output voltage VO. Voltage must be +5V DC.

Troubleshooting[edit | edit source]

Problem Solution
Nothing (0V) on VI
  1. Ensure the power switch wasn't OFF during your check (it happens to the best of us).
  2. Test D2 diode.
  3. Test power switch (both positions and GND).
    • Power switch isn't faulty? Multiple options here:
      • CN4 barrel socket could be faulty, check solder points.
      • On 171-6395A/171-5922A:
        • Test C41 capacitor. Visual check for any bulging first.
      • On 171-5926-A:
        • Test C50 and C52 capacitors. Visual check for any bulging first.
      • Check JV and JG ferrite beads for continuity and absence of high impedance.
      • PCB trace is cut.
Nothing (0V) on VO
  1. Ensure the power switch wasn't OFF during your check (it happens to the best of us).
  2. Check continuity:
    • On 171-5926-A:
      • Between the input pin VI and positive pin on C50.
      • Between the center pin GND and the ground plane.
      • Between the output pin V0 and C52.
    • On 171-6395A/171-5922A:
      • Between the input pin VI and positive pin on C41.
      • Between the center pin GND and the ground plane.
      • Between the output pin V0 and CP resistor right next to IC8.
  3. In some rare cases, the component pads could be busted.
  4. Still nothing? The voltage regulator is faulty, replace the component.
More or less than 5V DC ± 5% on VO

Replacement[edit | edit source]

Virtually any 7805 (TO-220) will do the trick[note 2]

Troubleshooting power delivery[edit | edit source]

The idea here is to ensure every IC is powered correctly by checking every "voltage in" pins.

Procedure[edit | edit source]

Check for VCC (+5V DC) presence on:

171-5926-A 171-6395A/171-5922A
  • Pin 11 on IC1.
  • Pin 28 on IC2.
  • Pin 28 on IC3.
  • Pin 32 on IC4.
  • Pin 18 and 60 on IC5.
  • Pin 28 on IC6 and IC7.
  • (NTSC only) Pin 12 and 19 on IC9.
  • Pin 11 on IC1.
  • Pin 28 on IC2.
  • Pin 26 on IC3.
  • Pin 48 on IC4.
  • Pin 18 and 40 on IC5.
  • Pin 28 on IC6 and IC7.
  • Pin 12 and 19 on IC9.

Troubleshooting[edit | edit source]

Problem Solution
+5V DC missing on a pin

There is no magic answer here:

  • Follow the via (or the schematics if you have them) until you find the culprit.
  • If every component is OK between VCC and your pin, the PCB trace is cut.

Troubleshooting the RESET circuit[edit | edit source]

The RESET circuit is active low (active at 0V); Any continuous 0V level will trigger a reset loop and prevent the board from initializing.
That's why we need to check for VCC (+5V DC) presence on every RESET pin.

Procedure[edit | edit source]

Check for VCC (+5V DC) presence on:

171-5926-A 171-6395A/171-5922A
  • Pin 26 on IC1.
  • Pin 41 on IC4.
  • Pin 23 on IC5.
  • Pin 46 on CN1.
  • Pin 26 on IC1.
  • Pin 46, 47 on IC4.
  • Pin 23 on IC5.
  • Pin 46 on CN1.

Troubleshooting[edit | edit source]

Problem Solution
+0V on one or multiple pins
  • The most common issue is a faulty C18/C2 capacitor.
  • The R3/R4 resistor could be faulty too.
  • (171-6395A/171-5922A only) IC4 is handling RESET IN and RESET OUT it could also be faulty.

Troubleshooting the clock circuits[edit | edit source]

Procedure[edit | edit source]

171-5926-A 171-6395A/171-5922A Waveform [note 3]
Check the clock on the XTAL oscillator, frequency should be 10.738635MHz ± 100Hz. Check the clock on the XTAL oscillator, frequency should be 53.203424MHz ± 100Hz. -
- Check for a 4.43361875MHz ± 30Hz on:
  • Pin 42 on IC4.
 -
Check for a 10.738635MHz ± 100Hz clock on:
  • Pin 34/35 on IC5.
 Check for a 10.738635MHz ± 100Hz clock on:
  • Pin 41 on IC4.
  • Pin 34/35 on IC5.
 Master System II XTAL reference
Check for a 3.579545MHz ± 30Hz clock on:
  • Pin 6 on IC1.
  • Pin 47 on CN1.
 Check for a 3.579545MHz ± 30Hz clock on:
  • Pin 6 on IC1.
  • Pin 47 on CN1.
 Master System II 3.58MHz reference

Integrated Circuits[edit | edit source]

IC BD M4Jr. VA1 IC BD M4Jr. PAL IC BD M4Jr. PAL 2M IC BD M4Jr. VA1 (RGB) Function
IC8 MC7805 L7805CV L7805CV LM340TS, L7875CT Voltage regulator; produces VCC. Transforms the output voltage produced by the AC/DC adapter (+9V DC ± 10%) to a reference voltage named VCC (+5V DC ± 5%) that will act as the main power rail.
IC1 Z0840004PSC Z0840004PSC Z0840004PSC Z0840004PSC CPU -
IC2 MPR-12808 MPR-12808 (W63), MPR-12808F MPR-15155 (T62) MPR-12808 (W63) BIOS ROM Boots the system, handles the splash screen, anti-piracy and region locking and starts the game.
This ROM can also contain a built-in game (after the first 8KB dedicated to the BIOS).
IC3 D4168C-15 D4168C-15-SG, KM6264BL-10, LC3664RL D4168C-15-SG, LC3664BL-10 LC3664BL-10, HM6265L-90 RAM General purpose SDRAM.
IC4 315-5216 315-5237 315-5237 315-5216 I/O Controller Interfaces with the gamepads and accessories.
IC5 315-5246 315-5246 315-5246 315-5246 Video Display Processor Commonly referred to as the VDP, it handles graphics and audio.
IC6 D4168C-15 D4168C-15-SG D4168C-15-SG D4168C-15 VRAM SDRAM dedicated to the VDP.
IC7 D4168C-15 D4168C-15-SG D4168C-15-SG D4168C-15 VRAM SDRAM dedicated to the VDP.
IC9 CXA1145P CXA1145P MB3514 - Video Encoder Receives analog RGB and composite synchronous signals and outputs NTSC/PAL composite, luminance, chrominance and RGB video signals.

Additional Information[edit | edit source]

Sega Master System II ground plane
Master System II ground plane

What is the device power input?[edit | edit source]

  • +9V DC ± 10%, 0.5A.
  • 5.5mm x 2.1mm barrel plug.
  • Center-pin negative.png
    Center-pin negative polarity (tip: +9V DC, sleeve: -9V DC).

Where I can find GND on the board?[edit | edit source]

The ground plane is present all around the board as a large copper via (see picture).

Notes[edit | edit source]

  1. ↑ Why not +9V DC here?
    VIN goes through a diode D2 before reaching IC8. D2 is a silicon diode rectifier, and they always have a forward voltage drop (≈ 0.55V at 0.5A for a 1SR35-100). stock IC8 can operate with a voltage as low as +7V DC, so we're good.
  2. ↑ Want to pick your own voltage regulator?
    • You may want to choose a TO-220 package if you want a drop-in replacement (same pins and pitch).
    • Make sure the pinout is correct (VI, GND, VO).
    • The regulator must provide a +5V DC nominal output voltage VO.
    • And accept a +9V DC input voltage VI (check the minimum and maximum input voltages too).
    • It's advisable to double-check the dropout voltage Vd (The difference between the input and output voltages for the voltage regulator to work).
      We have a +4V DC difference between VI and VO in our context, so we need to make sure the dropout voltage is lower than +4V DC.
    • IC8 will provide a critical reference voltage: keep the tolerance as low as possible ≤5% (the tolerance is the output voltage accuracy).
    • Keep the junction-to-air thermal resistance (usually named θJA) as low as possible.
  3. ↑ Don't buy an oscilloscope to check the crystal oscillator if you don't already own one! Desolder the oscillator and measure it with the frequency function/mode on your DMM will do the trick.
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