Sega Mega Drive / Genesis (Model 2): Difference between revisions
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Introduced in '''1993''', it condenses the original two-board architecture into a single cost-reduced PCB that integrates more logic into the '''315-5660 “M5” ASIC''', deletes the headphone amplifier, and replaces the large 8-pin DIN with a '''mini-DIN-9''' A/V port. | Introduced in '''1993''', it condenses the original two-board architecture into a single cost-reduced PCB that integrates more logic into the '''315-5660 “M5” ASIC''', deletes the headphone amplifier, and replaces the large 8-pin DIN with a '''mini-DIN-9''' A/V port. | ||
== | == Historical Context == | ||
* Development began mid-1992 to cut manufacturing cost (fewer PCBs, chassis tooling shared with '''Model 2 Sega CD'''). | * Development began mid-1992 to cut manufacturing cost (fewer PCBs, chassis tooling shared with '''Model 2 Sega CD'''). | ||
* Launched '''23 April 1993''' in Japan bundled with *Sonic CD* coupons; reached U.S./EU retail in October 1993 at a launch price of '''US $99''' (console + ''Sonic 2''). | * Launched '''23 April 1993''' in Japan bundled with *Sonic CD* coupons; reached U.S./EU retail in October 1993 at a launch price of '''US $99''' (console + ''Sonic 2''). | ||
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* Total Genesis/Mega Drive family sales surpassed '''30 million''' units worldwide; ~40 % are estimated to be Model 2 boards (VA0-VA4, Majesco VA7/GOAC). | * Total Genesis/Mega Drive family sales surpassed '''30 million''' units worldwide; ~40 % are estimated to be Model 2 boards (VA0-VA4, Majesco VA7/GOAC). | ||
== | == Hardware Architecture == | ||
{| class="wikitable" style="width:70%; text-align:center;" | {| class="wikitable" style="width:70%; text-align:center;" | ||
|+'''Integrated ICs (VA1 reference)''' | |+'''Integrated ICs (VA1 reference)''' | ||
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*CSYNC no longer present—mods tap VDP pin 11. | *CSYNC no longer present—mods tap VDP pin 11. | ||
== | == Motherboard Revisions == | ||
{| class="wikitable" style="width:95%; text-align:center;" | {| class="wikitable" style="width:95%; text-align:center;" | ||
|+'''Model 2 VA Boards''' | |+'''Model 2 VA Boards''' | ||
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Errata: VA1 consoles can exhibit “rainbow jail-bars” due to shared RGB line impedance; mitigated by installing 470 Ω series resistors or full Triple-Bypass mod. | Errata: VA1 consoles can exhibit “rainbow jail-bars” due to shared RGB line impedance; mitigated by installing 470 Ω series resistors or full Triple-Bypass mod. | ||
== | == Audio Path == | ||
1. YM3438 DAC (inside ASIC) → 2. passive RC low-pass → 3. 315-5684 mixer → 4. Sony CXA1645 (NTSC) or MB3514 (PAL) video encoder → 5. mini-DIN audio pins. | 1. YM3438 DAC (inside ASIC) → 2. passive RC low-pass → 3. 315-5684 mixer → 4. Sony CXA1645 (NTSC) or MB3514 (PAL) video encoder → 5. mini-DIN audio pins. | ||
No headphone amp, therefore no PWM scaling knob; DC bias ~1.3 V, so improper cable coupling causes “mono bleed” on some TVs. | No headphone amp, therefore no PWM scaling knob; DC bias ~1.3 V, so improper cable coupling causes “mono bleed” on some TVs. | ||
== | == Servicing & Maintenance == | ||
* '''Capacitors''' – fewer electrolytics; critical audio rails: C68 (47 µF/16 V), C41 (22 µF), C9 (10 µF 315-5684). | * '''Capacitors''' – fewer electrolytics; critical audio rails: C68 (47 µF/16 V), C41 (22 µF), C9 (10 µF 315-5684). | ||
* '''DC jack''' – fragile centre pin; desolder & replace with Kycon KLDX-2.5A for loose-power issues. | * '''DC jack''' – fragile centre pin; desolder & replace with Kycon KLDX-2.5A for loose-power issues. | ||
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Comprehensive procedures: see [[Sega Mega Drive / Genesis (Model 2) Maintenance Guide]] and [[Sega Mega Drive / Genesis (Model 2) Capacitor Replacement Guide]]. | Comprehensive procedures: see [[Sega Mega Drive / Genesis (Model 2) Maintenance Guide]] and [[Sega Mega Drive / Genesis (Model 2) Capacitor Replacement Guide]]. | ||
== | == Troubleshooting Cheatsheet == | ||
{| class="wikitable" style="width:88%;" | {| class="wikitable" style="width:88%;" | ||
! Fault !! Likely Cause !! Remedy | ! Fault !! Likely Cause !! Remedy | ||
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|} | |} | ||
== | == Popular Mods == | ||
* '''Rapid-fire switch''' (JP2) – solder toggle to TH input via 74HC04. | * '''Rapid-fire switch''' (JP2) – solder toggle to TH input via 74HC04. | ||
* '''Region + 50/60 Hz''' – wire JP3/JP4 to 3-way slide; TMSS bios auto-selects RGB palette accordingly. | * '''Region + 50/60 Hz''' – wire JP3/JP4 to 3-way slide; TMSS bios auto-selects RGB palette accordingly. | ||
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* '''MiSTer Analogue IO''' – Model 2 shell often re-purposed as FPGA console. | * '''MiSTer Analogue IO''' – Model 2 shell often re-purposed as FPGA console. | ||
== | == Technical Resources == | ||
* Mega Drive II Service Manual (Sega, 1993) – schematics VA1 & VA2. | * Mega Drive II Service Manual (Sega, 1993) – schematics VA1 & VA2. | ||
PDF links available at [[:Category:Sega Service Manuals|Sega Service Manuals]]. | PDF links available at [[:Category:Sega Service Manuals|Sega Service Manuals]]. | ||
== | == Trivia == | ||
* Early Model 2 NTSC boards left “GAMES = TOYS?” text in ROM v2.00; never displayed. | * Early Model 2 NTSC boards left “GAMES = TOYS?” text in ROM v2.00; never displayed. | ||
* Bundles: ''Sonic 2'' (“Not For Resale”) cart in U.S.; ''The Lion King'' in PAL territories (1994). | * Bundles: ''Sonic 2'' (“Not For Resale”) cart in U.S.; ''The Lion King'' in PAL territories (1994). | ||
* Brazilian licensee '''Tec Toy''' produced a turquoise “Mega Drive 3” reuse of Model 2 VA3 until 2007. | * Brazilian licensee '''Tec Toy''' produced a turquoise “Mega Drive 3” reuse of Model 2 VA3 until 2007. | ||
== | == See Also == | ||
* [[Sega Mega Drive (Model 1)|Sega Mega Drive / Genesis (Model 1)]] – original “high-def” hardware | * [[Sega Mega Drive (Model 1)|Sega Mega Drive / Genesis (Model 1)]] – original “high-def” hardware | ||
* [[Sega CD (Model 2)]] – side-loading optical add-on | * [[Sega CD (Model 2)]] – side-loading optical add-on | ||