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SEGA Master System II
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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 |
---|
|
Troubleshooting[edit | edit source]
Problem | Solution |
---|---|
Nothing (0V) on VI |
|
Nothing (0V) on VO |
|
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 |
---|---|
|
|
Troubleshooting[edit | edit source]
Problem | Solution |
---|---|
+5V DC missing on a pin |
There is no magic answer here:
|
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 |
---|---|
|
|
Troubleshooting[edit | edit source]
Problem | Solution |
---|---|
+0V on one or multiple pins |
|
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:
|
- |
Check for a 10.738635MHz ± 100Hz clock on:
|
Check for a 10.738635MHz ± 100Hz clock on:
|
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Check for a 3.579545MHz ± 30Hz clock on:
|
Check for a 3.579545MHz ± 30Hz clock on:
|
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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]
What is the device power input?[edit | edit source]
- +9V DC ± 10%, 0.5A.
- 5.5mm x 2.1mm barrel plug.
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]
- ↑ 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. - ↑ 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 betweenVI
andVO
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.
- ↑ 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.