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Sega Mega Drive / Genesis

Sega's 16-bit console (1988). Mega Drive in Japan, Europe and most of the world; Genesis in North America. Native RGB output, a cult FM sound chip, and many hardware revisions that change the sound and video.

Status: under construction

The capacitor values and precise locations will come from a verified source (ConsoleMods, CC-BY-SA) — nothing is invented here.

Summary of linked pages

Identification

Field Value
Manufacturer Sega
Release year 1988 (JP), 1989 (NA, "Genesis"), 1990 (EU)
Generation 4th (16-bit)
Hardware revisions Model 1: VA0 → VA7; Model 2; Model 3
Native video output Composite + native RGBs (multi-out); RF on Model 1
Region / lockout Region lock (cartridge shape + check) + 50/60 Hz
Media format ROM cartridge; Mega-CD, 32X add-ons

Architecture

Block Component Notes
Main CPU Motorola 68000 @ ~7.67 MHz (NTSC) 16/32-bit core
Secondary CPU Zilog Z80 @ ~3.58 MHz Sound; Master System backward-compat (via Power Base Converter)
Video (VDP) Sega 315-5313 320×224 (NTSC) / 320×240 (PAL); 512 palette, ~61 on screen
FM sound Yamaha YM2612 (early) / integrated YM3438 (Model 2) 6 FM channels, 1 PCM channel
PSG sound TI SN76489 Integrated in the VDP; 3 voices + noise

Revisions & differences (the key collector point)

The sound changes by revision — that's THE big story of the machine.

Revision Sound chip "Ladder effect" Notes Status
Model 1 VA0–VA3 discrete YM2612 Yes ("crunchy" sound) Loud audio, noisier to confirm
Model 1 VA6/VA6.5/VA7 ASIC integration TMSS arrives
Model 2 integrated YM3438-type No Cleaner, finer sound; SMD caps
Model 3 integrated No No clean RGB, no ext. port —

This VAx → chip/sound table must be verified unit by unit (online lists diverge). To be pinned down with a reliable source.

Disassembly (Model 1) — tutorial

Number/type of screws to confirm per revision. No HV here (it's not a CRT), but unplug the power first.

  1. Flip the console over, remove the bottom screws (Phillips).
  2. Separate the top shell from the bottom.
  3. Remove the RF shield (metal cage): unfold the tabs / screws.
  4. Take the motherboard out of the bottom shell.
  5. Orientation: locate the PSU/fuse F1, multi-out, YM/PSG, region area.

Disassembly sequence (Model 2 example)

Closed Genesis Model 2 console
1. Closed console — flip over, remove the bottom screws.
RF shield in place on the board
2. Shell open: the RF shield covers the board (screws aligned on the left).
Removing the RF shield
3. Shield removed — the board appears.
Motherboard removed from the shell
4. Board removed from the shell.

Frames extracted and cropped from the TRU Fixes teardown video (Model 2), CC-BY 3.0.

Model 1 stills — to complete

The sequence above is a Model 2. Model 1 stills are still missing — ideally your own photos (original heritage), e.g. md1-vis-dessous, md1-carte-verso. Full video teardown (CC-BY 3.0): Sega Genesis 2 — Complete Teardown & Cleaning — TRU Fixes.

Once the board is out, with the components identified:

123 456 789 101112
Mega Drive Model 1 (PAL, 1992) motherboard. Photo: Bill Bertram (Pixel8), CC-BY-SA 3.0 — annotations: this wiki.
  1. RF modulator (MIT60M)
  2. 68000 CPU (HD68HC000P8)
  3. VDP (SEGA 315-5313A)
  4. FM sound (Yamaha YM2612)
  5. Z80 (sound / Master System backward-compat)
  6. Work RAM (MCM51L832 ×2)
  7. Crystal 53.203 MHz
  8. Cartridge slot
  9. Expansion port (edge connector)
  10. Controller ports (×2)
  11. Region jumpers (JP…) — for the region-free mod; this board already has a wired mod (purple/blue/brown wires)
  12. Switches (SW1 reset / power)

Key component locations

123 456 789 1011
Genesis Model 2 VA0 (USA) board, component side. Photo: Evan Amos (Vanamo Media), public domain — annotations: this wiki.
  1. 68000 CPU (MC68HC000FN8)
  2. Work RAM (MCM51L832 ×2)
  3. VDP (SEGA 315-5487)
  4. VRAM (MB81461 ×2)
  5. Master crystal 53.693 MHz
  6. Cartridge slot
  7. Expansion port (edge connector)
  8. Controller ports (×2)
  9. DC power + A/V output
  10. Regulator (under a heatsink)
  11. Capacitor area — SMD, targets of the recap (see below)

Common faults

Symptom Likely cause Repair
Nothing at power-on Reversed centre-negative PSU → blown fuse F1 Check/replace F1; use the right PSU
Degraded sound/video (Model 2) Leaking SMD caps Recap (see below)
Cartridge not read / corrupted graphics Cartridge connector oxidation Clean with iso alcohol
Flaky controller Worn port / dead series diode or resistor Replace the component
Loss of a sound channel YM or mixing stage Probe diagnosis

Original service manual ✅

Manufacturer manual archived locally. It typically carries the schematics, the block diagram, the expected voltages and waveforms, the parts list and the disassembly procedures — the reference when a symptom matches no known fault.

  • Mega Drive II / Genesis II — service manual (PAL-B/I/G RGB, 1993) — PDF

Status

A manufacturer document with no explicit licence, kept for preservation (machine long out of production). Source: Internet Archive.

Step-by-step disassembly procedures ✅

5 procedures transcribed from the iFixit guides, with their difficulty and estimated time.

Procedure Difficulty Time
How to clean the Sega Genesis game port Very easy 5 minutes
Sega Genesis Reset Button Repair Easy 5 - 10 minutes
Sega Genesis Motherboard Replacement Moderate 15 - 20 minutes
Sega Genesis Outer Case Replacement Moderate 10 minutes
Sega Genesis Power LED Replacement Easy 10 minutes
How to clean the Sega Genesis game port
  1. Fold fine grit sand paper over a credit card.
  2. Rub credit card with sand paper up and down vertically inside the game cartridge port.
  3. Blow out game cartridge port using a can of compressed air. Warning: Do not turn the aerosol can upside down as you spray.
  4. Rub a Q-tip dipped in rubbing alcohol along the pins of the cartridge slot to remove any remaining debris.
Sega Genesis Reset Button Repair

We all know that the Sega Genesis brought to us...

  1. Remove the six screws from the underside of the console with a Phillips #1 screwdriver.
  2. Flip the Sega Genesis upright.
  3. Gently lift the top casing. Note: the case will be connected to the main board by LED wires.
  4. Bend out the LED leads into vertical positions.
  5. Slide the LED wire apparatus off the lead pins. Note: observe which color wire corresponds with which length of pin.
  6. Separate the main board from the outer case.
  7. Using Philips screwdriver, remove 11 screws securing silver casing.
  8. Remove silver case.
  9. Locate reset button on motherboard
  10. Place three pieces of 1cm x 1cm masking tape over reset button.
Sega Genesis Motherboard Replacement
  1. Remove the six screws from the underside of the console with a Phillips #1 screwdriver.
  2. Flip the Sega Genesis upright.
  3. Gently lift the top casing. Note: the case will be connected to the main board by LED wires.
  4. Bend out the LED leads into vertical positions.
  5. Slide the LED wire apparatus off the lead pins. Note: observe which color wire corresponds with which length of pin.
  6. Separate the main board from the outer case.
  7. Remove single black screw from the outside of the bottom cover, using a Philips screwdriver.
  8. Using a Philips screwdriver, remove 11 screws securing silver casing.
  9. Remove silver case.
  10. Remove single golden screw on motherboard using Philips screwdriver. Note: Push headphone jack to the side.
  11. Remove two black screws on the left and right sides of the cartridge slot.
  12. Remove motherboard.
  13. Re-install new motherboard.
Sega Genesis Outer Case Replacement

This repair guide will take you through all the...

  1. Remove the six screws from the underside of the console with a Phillips #1 screwdriver.
  2. Flip the Sega Genesis upright.
  3. Gently lift the top casing. Note: the case will be connected to the main board by LED wires.
  4. Bend out the LED leads into vertical positions.
  5. Slide the LED wire apparatus off the lead pins. Note: observe which color wire corresponds with which length of pin.
  6. Separate the main board from the outer case.
Sega Genesis Power LED Replacement

This repair guide wil give a walk through on...

  1. Remove the six screws from the underside of the console with a Phillips #1 screwdriver.
  2. Flip the Sega Genesis upright.
  3. Gently lift the top casing. Note: the case will be connected to the main board by LED wires.
  4. Bend out the LED leads into vertical positions.
  5. Slide the LED wire apparatus off the lead pins. Note: observe which color wire corresponds with which length of pin.
  6. Separate the main board from the outer case.
  7. Remove plastic "Power / On" cover by pushing tabs together.
  8. Pull "Power / On" cover away from the console cover.
  9. From the outside of the top cover, remove LED.
  10. Insert new LED (here to buy LED.)
  11. Re-insert "Power / On" cover until it clicks into place.

Source and licence

iFixit guides, published under Creative Commons BY-NC-SA — reuse permitted with attribution, non-commercial use and share-alike. Of all the documentation gathered here, this is the only material under an explicit licence; the manufacturer manuals have none. The step photos remain on iFixit — only the text is reproduced.

Detailed recap

The BOM depends on the exact board revision

Each revision (VA0, VA1, VA1.8, VA2…) has its own layout. Always follow the cap map matching YOUR board. The lists below only apply to the indicated revision. If in doubt, refer to the ConsoleMods cap map for your revision (link below).

Tools & materials (after ConsoleMods)

  • Soldering iron: avoid a conical tip, prefer a chisel tip (better board/lead contact).
  • Solder: leaded preferably (easier, matches the original).
  • (Option) desoldering iron; otherwise desoldering braid or a pump.
  • Replacement capacitors (see the per-revision list).
  • Isopropyl alcohol ≥ 90% + something to scrub away the flux and leaked electrolyte.
  • (Option) ultrasonic cleaner.

Good practice: Model 2 = electrolytic SMD caps (leak, recap as a priority); Model 1 = through-hole, more robust. Photo before desoldering for polarity/orientation. Respect the value (µF), voltage (V) ≥ original, and the polarity. Quality 105 °C caps.

Model 1 (IC BD M5, base 837-6656) ✅ verified list

Source: Console5 TechWiki. 36 radial electrolytic capacitors (through-hole). Grouped shopping list:

Value Voltage Quantity
1 µF 50 V 6
10 µF 10 V 1
10 µF 16 V 11
47 µF 10 V 8
100 µF 10 V 7
220 µF 10 V 2
220 µF 16 V 1
Full per-reference list (C1 → C74) — expand
Ref µF V Ref µF V
C1 220 16 C52 100 10
C4 100 10 C53 100 10
C5 10 16 C55 10 16
C6 47 10 C57 10 16
C13 10 16 C58 1 50
C24 100 10 C59 47 10
C30 10 16 C60 47 10
C31 10 16 C61 1 50
C32 100 10 C62 1 50
C38 10 16 C63 47 10
C40 1 50 C64 10 16
C41 10 10 C65 47 10
C42 1 50 C66 47 10
C43 10 16 C67 47 10
C44 1 50 C68 47 10
C49 100 10 C71 10 16
C50 220 10 C72 10 16
C51 220 10 C74 100 10

Model 1 — variations per revision (Δ vs base) ✅

Source: Console5 TechWiki. Base = IC BD M5 / 837-6656 (list above). Below, only what changes for each revision. C1 stays 220 µF/16 V everywhere (except VA7).

VA1 — 837-6832 (38 caps)
  • Removed: C6 (47 µF/10 V)
  • 47 µF: 10 V → 16 V: C59, C60, C63, C65, C66, C67, C68
  • Additions: C23 (100/10), C79 (100/16), JPx (47/16)
VA2 — 837-6955 (37 caps)
  • Removed: C6
  • 10 µF: 16 V → 25 V: C5, C13, C30, C31, C38, C41, C43, C55, C57, C64, C71, C72
  • C32: 100/10 → 220/10
  • 47 µF: 10 V → 16 V: C59, C60, C63, C65, C66, C67, C68
  • Additions: C23 (100/10), C79 (100/16)
VA2 USA — 837-6992 (39 caps)
  • Removed: C6
  • C32: 100/10 → 220/10
  • 47 µF: 10 V → 16 V: C59, C60, C63
  • Additions: C23 (100/10), C79 (100/16), C86 (100/10), JPx (47/10)
VA3 USA — 837-7071 (40 caps)
  • Removed: C6
  • C32: 100/10 → 220/10
  • 10 µF: 16 V → 25 V: C41, C43, C55, C64
  • 47 µF: 10 V → 16 V: C59, C60, C63, C65, C66, C67, C68
  • Additions: C23 (100/10), C79 (100/16), C86 (100/10), JPx (47/16)
  • ⚠ On the back: BOT 220 µF/6.3 V (VRAM side, VCC pin 18)
VA4 PAL — 171-5872-20 (38 caps)
  • Removed: C6
  • C32: 100/10 → 220/10
  • C41: 10/10 → 10/16
  • Additions: C23 (100/10), C79 (100/16), C86 (100/10)
VA6 — IC BD M5 / USA VA6 (39 caps)
  • Removed: C6, C67
  • C32: 100/10 → 220/10
  • C41: 10/10 → 10/16
  • Additions: C23 (100/10), C79 (100/16), C86 (100/10), C111 (47/10), C112 (10/16)
VA7 — PC BD M5 USA (171-6217-11) — 31 SMD caps (CE series)

A transition board: no longer the through-hole C series, but CE-series SMD (like Model 2). Shopping list:

Value Voltage Quantity
10 µF 16 V 17
47 µF 16 V 7
100 µF 10 V 3
220 µF 10 V 2
220 µF 16 V 2

Model 2 (Genesis 2, CE / SMD series) ✅ verified lists

Electrolytic SMD caps (CE series). Sources: ConsoleMods and Console5 (both agree on VA0/VA1/VA1.8 → good confidence).

VA0 / VA1 / VA1.8 — 32 capacitors:

Quantity Value (µF) Voltage (V)
20 10 16
7 47 10
2 100 10
2 220 6.3
1 220 16
VA2 / VA2.3 USA — 30 caps
Quantity Value (µF) Voltage (V)
15 10 16
7 47 10
4 100 10
1 2.2 50
1 22 50
1 220 6.3
1 220 16
VA3 USA — 23 caps
Quantity Value (µF) Voltage (V)
10 10 16
5 47 10
4 100 10
1 2.2 50
1 22 50
1 220 6.3
1 220 16
VA4 USA — 23 caps
Quantity Value (µF) Voltage (V)
9 47 10
6 10 16
4 100 10
1 2.2 50
1 22 16
1 220 6.3
1 220 16

Genesis 3 (Majesco, compact) ✅ verified lists

Source: Console5 TechWiki. The Genesis 3 is a late compact model (Majesco). Chips (VA2): 315-6123 ("Genesis-on-a-chip"), SDRAM, RGB encoder CXA1645M, LM324, 7805 regulator.

Genesis 3 — MD3 VA1 (12 caps)
Ref µF V
CE1 220 16
CE2, CE9 100 10
CE3, CE4, CE5, CE6, CE12 47 16
CE7 220 6.3
CE8, CE10, CE11 10 50
Genesis 3 — MD3 VA2 (171-7652D) — 18 caps
Ref µF V
CE1, CE5, CE18 100 10
CE2 220 6.3
CE3, CE6, CE8, CE9, CE10, CE12, CE13, CE14, CE15 47 16
CE4, CE7, CE11 10 50
CE17 220 16
CE19 330 6.3

Covered here & remaining variants

Transcribed and verified above: Model 1 (base + VA1→VA7), Model 2 (VA0→VA4), Genesis 3 (VA1/VA2); Nomad and CDX / Multi-Mega + Wondermega on their pages. No clean text list on Console5 (empty pages): X'Eye, Mega Jet → not transcribed (nothing invented).

Sources (both block auto-fetch → browser reading):

We invent no value: every line comes from a verified source, transcribed with attribution.

Video outputs & quality

  • Native RGBs on the multi-out (Model 1 and 2): no mod required for RGB, just the right SCART cable.
  • Noisy audio on Model 1: noisy analog AV stage → hence the bypass mods.
  • Video connector: 8-pin DIN (early Model 1) then 9-pin mini-DIN.

Indicative prices · revision marking

A moving market → we name the maker + reseller. The VDP pins are identical across all revisions (315-5313), but the physical layout (component/via locations, top- or bottom-install) depends on the revision (the "VAx" marking on the back) — check it before drilling/cutting. Procedures transcribed from ConsoleMods (CC-BY-SA). Soldering: 🟢 none · 🟡 beginner · 🟠 confident · 🔴 expert.

Clean video + audio — the Triple Bypass (the reference AV mod)

  • What it is: a board that bypasses the audio and video stages (and optionally the Model 1 DIN) for RGB + audio free of motherboard noise. Originally designed by db Electronics, now open-source (files on Tianfeng's GitHub, Zaxour's remix).
  • Benefit: Model 1 = a big video upgrade; Model 2/3 = mostly the audio (often mono stock). Fixes jailbars (vertical bars) — failing that, lifting the VDP subcarrier pin already reduces them.
  • ⚠️ Expert 🔴 and disables composite output in most cases. Install per revision (Model 1 VA0→VA7, Model 2 VA0→VA4, Model 3, CDX); Model 2 (except VA4) → bottom-install recommended.
  • Where to buy: Insurrection Industries, RetroGamerStuff (or build it, it's open-source).
  • Illustrated per-board step-by-step: ConsoleMods: Triple Bypass · internal page Triple Bypass.

RGB is native — a bypass doesn't add RGB, it improves it

Model 1 and Model 2 already output RGB on the multi-out → for RGB, a cable is enough. The bypass (Triple Bypass or the DIY below) exists to strip the noise/jailbars from the stock amp.

Exact points for the Model 1 RGB bypass (VDP 315-5313 + CXA1145 amp) (transcribed from ConsoleMods, CC-BY-SA)

Expert 🔴, irreversible mod; the author recommends a ready-made Triple Bypass board instead. Revisions differ — verify every pin on your board.

Tap RGBS on the Sega 315-5313 VDP (carefully lift these — fragile pins):

Signal 315-5313 VDP pin
Red 27
Green 28
Blue 29
Composite sync 54

"RAM noise" fix (placement is crucial, else the bypass amplifies the noise): a capacitor between the 5 V and ground pins next to the RGB pins on the via (as close as possible); a 2nd capacitor on the output of pin 54. If you lift the RGB pins, recreate the pull-up circuit (ConsoleMods RGB Bypass Color Fix page). Do not remove the stock CXA encoder.

Output to the stock multi-out: the encoder is a Sony CXA1145. Its pins 23 / 22 / 21 / 11 = R / G / B / CSYNC and go to multi-out pins 7 / 3 / 8 / 1 respectively. To wire the new amp: cut/lift CXA1145 pins 23/22/21/11 (lifting = reversible), then wire the bypass outputs to those multi-out pins.

Audio only (without a full video bypass)

  • Crystal Clear Audio Mod (CCAM) or Mega Amp 2.0 Pro: improve the audio amp (Model 1 = noise, Model 2 = mono→stereo). Dedicated ConsoleMods guides (Crystal Clear Audio Mod, Mega Amp).
  • Preamp Fix (Model 1 VA0-VA2): fixes the slightly overdriven headphone audio of early boards — points/values below.
Model 1 preamp fix (VA0-VA2) — the overdriven headphone audio (transcribed from ConsoleMods, CC-BY-SA)

Early Japanese Mega Drives / US Genesis have a slightly overdriven headphone preamp (the stereo audio is otherwise clean and balanced). Fixed at the factory from VA3 on; on VA0, VA1 and VA2 (JP) — and US VA2 (different layout) — you fix it by substituting several component values. Mod by Ace (Sega-16 forum), the only audio mod approved by the 16-bit Audiophile Project for recording.

BOM (1206 SMD): 2× 10 kΩ, 1× 18 kΩ, 2× 4700 pF, 1× 33 kΩ, 28 AWG wire, optional: a TL972 op-amp (or similar).

⚠️ The exact "which reference gets which value" map is in ConsoleMods' per-revision pictures (VA0/VA1/ JP-VA2 on one side, US-VA2 on the other) — we don't invent it here (a value in the wrong place = wrong sound). The mod greatly reduces the mono volume (AV/RF).

Optional mono fix (US VA2, exact pins) — to restore mono volume: the op-amp is an 8-pin LM358 between the YM2612 and the CXA1145 encoder. Cut the traces of pins 1 and 2 to the negative leg of C30, then the trace joining pins 1↔2; cut the trace from pin 3. Connect pin 1 → C30 negative leg, and the original pin-3 trace → pin 2. After refitting the op-amp (or a socket), solder a 33 kΩ between pins 1 and 2. Finally, a wire from op-amp pin 3 → pin 5 of the Sony A1034 headphone amp.

Play your whole library (flashcart)

  • Mega EverDrive (Krikzz) — a microSD flashcart, plug-and-play 🟢 (inserts like a game). X3 / X7 / Pro versions per budget. → Flashcarts.
  • Mega SD (Terraonion) — a flashcart that also emulates the Mega-CD (no more CD drive). → Mega SD.

Region / de-zoning

Region is set by two pins (on the VDP or main ASIC): one for language (EN/JP), one for frequency (50/60 Hz). Each is tied high (5 V) or low (GND):

Console Language Frequency
JP / Korea low (JP) high (60 Hz)
US / Brazil high (EN) high (60 Hz)
Europe / PAL high (EN) low (50 Hz)
  • De-zoning = make these two lines switchable (2 switches, or a "switchless" mod driven by the pad). (Curiosity: region-locked JP games only check language, not frequency → playable at 50 Hz with language set to JP, but slower.)
  • ⚠️ The exact language/frequency pins depend on the model (VDP/ASIC) and live in per-board illustrated guides (consolesunleashed) or are handled by a premade switchless board — we don't invent them. Solderless alternative: a cartridge adapter / flashcart. Concept transcribed from ConsoleMods (CC-BY-SA). → Region-free & lockout.
  • Mega-CD: the region lock is in the CD BIOS (independent of the console) → a region-free BIOS or loading another-region BIOS via flashcart.
  • ⚠️ TMSS (VA6+/Model 2): some old/unlicensed carts refuse to boot.

Recap

  • Capacitor replacement: see the detailed per-revision recap (CXX tables below) — especially on the Mega-CD and SMD models. ConsoleMods Replacing Capacitors.

Add-ons

("Do the same thing" = a dedicated page per module, console/mod structure.) - Mega-CD / Sega CD → consoles/sega/mega-cd - 32X → consoles/sega/32x - Power Base / Master System Converter → power-base-converter

Peripherals

  • 3-button → 6-button pad: the 6-button pad (Fighting Pad, for Street Fighter II′) adds X/Y/Z + Mode. A few old games glitch with it → start them holding Mode (the pad then behaves as 3-button).
  • Multitap: Team Player (Sega) / 4-Way Play (EA) — up to 4 players.
  • Menacer (infrared light gun), Sega Activator (a motion-sensing ring, a clumsy forerunner), Mega Mouse.
  • Sega Channel (US): a modem cartridge on the TV cable to download games (1990s) — a dead service, content worth preserving.

Hardware quirks

  • TMSS (Trademark Security System): from VA6+/Model 2 Mega Drives, a check shows "PRODUCED BY OR UNDER LICENSE FROM SEGA" — some old/unlicensed cartridges may refuse to boot on those consoles.
  • Lock-on (Sonic & Knuckles): the S&K cartridge has a pass-through on top; stacking Sonic 2/3 on it unlocks combined content ("lock-on technology").
  • SVP (Sega Virtua Processor): a DSP in the cartridge of Virtua Racing — the only MD game with on-cart 3D acceleration.
  • Blast Processing: a marketing slogan (fast 68000/VDP DMA), not a dedicated chip — not to be taken literally.

Photos / assets

Images in img/. Coming: annotated overlays (references on the boards), teardown photos (screws, shield), back/solder side, cap maps per revision (from ConsoleMods, with attribution).

Advanced repair

Recap by revision (especially MD2 / VA4+, electrolytics) — see the detailed recap above. Cross-cutting methods: Recap · PCB fault-finding · Traces & vias.

Sources & attribution

Text:

Images:

Video:

Review & corrections

How this space is used

Spotted a wrong value, an outdated procedure, a chip reference that does not match your board? Say so here, with what you observed (model, board revision, serial number, measurement). Every report is cross-checked against a source before anything changes — an unverifiable correction is published as “reported by …, not cross-checked” rather than silently applied.

Reading is open to everyone; posting requires signing in with Discord. Reports from the wiki's declared reviewers are handled first; anyone else's are read too, but go through a human before anything is changed.