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Sega Power Base Converter (Master System Converter)

The adapter that runs Master System games on a Mega Drive / Genesis. It's not emulation: the Mega Drive already contains what's needed (a Z80 and a Master System-compatible VDP) — the converter just adapts the cartridge connector. Called the Power Base Converter in the US, Master System Converter in Europe, Mega Adaptor in Japan.

Power Base Converter
Power Base Converter fitted on a Genesis. Photo: Evan-Amos, Wikimedia Commons, public domain.

Identification

Field Value
Manufacturer Sega
Type Passthrough add-on (Mega Drive cartridge slot)
Function play Master System cartridges (Mark III/SMS) on the Mega Drive
Variants Power Base Converter (US) · Master System Converter I / II (EU) · Mega Adaptor (JP, + My Card slot)

Why it works (no emulation)

The Mega Drive is 8-bit backward-compatible by design:

  • Its Z80 (normally for sound) can act as the Master System CPU.
  • Its VDP 315-5313 includes a Master System-compatible mode (the MD VDP is a superset of the SMS / TMS9918 VDP).

→ In "8-bit mode", the Mega Drive natively runs a Master System game. The converter just physically adapts the slot (cartridge pinout/format) — no emulation chip.

Variants

  • Power Base Converter (US) / Master System Converter I (EU): the large model, for the Mega Drive / Genesis Model 1.
  • Master System Converter II (EU): a compact version, compatible with the Mega Drive 2 (the MD2 slot has a different shape → the large model doesn't fit).
  • Mega Adaptor (JP): adds a My Card slot (Sega Card) on top of cartridges.

Limits to know

  • No FM sound: Japanese SMS games with a YM2413 (FM) chip play in PSG only (the Mega Drive lacks the SMS FM chip).

  • No Game Gear (different format and screen).

  • Model 1 vs Model 2: check the right converter for your Mega Drive.
  • Region: SMS region logic can matter depending on the games.

Installation

None: it's a passthrough. Insert it into the Mega Drive cartridge slot, then the Master System cartridge into the converter. Power on → 8-bit mode.

Faults (rare)

The converter has no active electronics → almost nothing to repair. The only common fault is a bad contact:

Symptom Cause Lead
SMS game not read / crash Oxidised/bent contacts (MD slot or converter slot) Clean both edges (iso alcohol), reseat
Nothing in 8-bit mode Wrong variant (Model 1 vs 2) Check the right converter (see Variants)
"Poor" sound on a JP game No FM (normal) None; an MD hardware limit

Before / after

Criterion Mega Drive alone With the converter
Master System games no yes (native 8-bit mode)
FM sound (JP SMS) — no (PSG only)
Effort — adapter (no soldering)

Modern alternatives

The converter is passive, so there's nothing to "modernise" on it. But you can reach the same goal another way:

  • Mega Drive flashcart with SMS support: a Mega EverDrive (Pro/X7) plays Master System ROMs directly on the Mega Drive (via its Z80) — no converter or cartridges needed.
  • FM sound (JP SMS games): the converter never reproduces FM (no YM2413 on the MD). For FM, play on a real Master System (ideally with the FM mod if export) → see Master System § mods.
  • Video: the picture comes out of the Mega Drive → MD RGB/recap mods apply (see Mega Drive).

Where to find

  • Original Sega converters (second-hand) or community repros.
  • Guides: RetroRGB / Sega communities.

Procedure — a dead console, step by step ✅

This machine does not run on its own

It needs a Mega Drive. Before opening anything, prove the host is good with a plain cartridge — otherwise you spend the day inside the add-on for a fault that is not in it. → Mega Drive

What this adds

Ordered for a console, not for an arcade board: what kills these is almost never the CPU. It is, in real order, the power supply, the capacitors, the drive or the cartridge slot, and only then the logic. → PCB diagnosis

1. The power supply. Two cases, depending on the machine. External brick: ⚠️ read the marking on the machine, next to the socket, and check the adapter against it — voltage and polarity. A centre-negative machine fed centre-positive loses its fuse, sometimes its regulator; do not trust a third-party label or a generic tip. Internal supply (the machine plugs straight into the wall): mains is inside the shell. Unplug, wait, and confirm the large capacitors are discharged before touching the board. Either way, measure under load: a failing supply holds its voltage until it is asked for current.

2. The fuse. Many of these machines have one right behind the socket — it is the part designed to die. Test it in continuity, out of circuit. A fuse that blows again is a short, not a fuse problem.

3. Capacitors. On most machines of this age this is the default suspect rather than a last resort — leaking SMD electrolytics eat the tracks underneath before they give any other sign. ⚠️ Not all of them are like that: some carry very few and are not recapped on principle. Read what this page says about it before reaching for the iron. → Recap

4. The cartridge connector. Cartridge contacts with isopropyl alcohol, never an abrasive eraser: it takes the gold plating off and the problem comes back worse. On the machine side, inspect the slot pins — splayed, bent or oxidised — and check continuity between slot and board.

5. Video output. Isolate the machine from the display: another cable, another TV, another input. A sizeable share of "dead consoles" are a dead cable, or a display that will not lock onto what this machine outputs — see the video section of this page for what that is.

6. Still nothing. Now, and only now, the logic: rails on the board, reset, clock, bus. → PCB diagnosis

Photos / assets

(To add: Power Base Converter vs Converter II, on the MD, slot.)

Advanced repair

A simple adapter (SMS → Mega Drive): cartridge contacts, little to repair. Methods: PCB fault-finding · Traces & vias.

Sources & attribution

Image:

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.