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Midway T-Unit (Mortal Kombat II, NBA Jam…)

The Midway T-Unit hardware (early 90s): a TMS34010 (graphics processor) running Mortal Kombat II, NBA Jam, NBA Jam T.E. and a T-unit version of Mortal Kombat. Digitised actors, big sprites, and ADPCM sound (Williams board) or DCS depending on the game. A descendant of the Y-Unit (Smash TV, Total Carnage, original MK1).

Identification

Field Value
Manufacturer Midway / Williams (WMS)
Years ~1992-1994
Type ROM-board platform; TMS34010 CPU/video
Connector type Midway harness (not JAMMA)
Settings DIP + CMOS (coinage can come from either)

Architecture

Block Chip Clock Role
CPU / video TMS34010 (GSP, Graphics System Processor) 50 MHz CPU and graphics engine (integrated blitter, framebuffer)
Video framebuffer driven by the TMS34010 pixel ~4 MHz big digitised sprites, wide palette
Sound (MK1 T-unit) Williams ADPCM board: M6809 + YM2151 + OKI6295 FM + samples
Sound (MK2, NBA Jam) DCS (Digital Compression System, ADSP-2105) high-quality compressed ADPCM audio
Settings/scores CMOS/NVRAM + a DIP bank bookkeeping, high scores

The TMS34010 is a graphics processor that serves both as CPU and display engine (bit-addressable, internal blitter) — hence the big digitised-actor sprites typical of MK/NBA Jam. The sound evolves: the Williams ADPCM board (6809/YM2151/OKI) on Mortal Kombat T-unit, then DCS (ADSP-2105 compression) on MK II and NBA Jam — a real audio quality jump.

Notable games

Mortal Kombat (T-unit version), Mortal Kombat II (1993), NBA Jam (1993), NBA Jam Tournament Edition (1994). The earlier Y-Unit (same TMS34010 family) carried Smash TV, Total Carnage, Mortal Kombat (1992) and Terminator 2.

Settings (DIP + CMOS)

Unlike the Williams 6809 (100% CMOS), the T-Unit has a real DIP bank — but hybrid: a "Coinage Source" switch chooses whether the coinage comes from the DIP or the CMOS. Gameplay settings (Attract Sound, "Low Blows", "Comic Book Offer"…) are on the DIP; bookkeeping and scores in CMOS. → Transcribed table: DIP settings — Mortal Kombat.

Common faults & preservation

Symptom Likely cause Lead
Lost settings / scores Flat / leaking CMOS battery Replace the battery; clean the corrosion
No sound (MK2/NBA Jam) DCS stage (ADSP-2105) DCS board diagnosis
No sound (MK1 T-unit) Williams ADPCM board (6809/YM2151/OKI) Sound-stage diagnosis
Corrupted sprites / page flipping Video RAM / TMS34010 RAM test, contacts
No image Power, TMS34010, harness Base diagnosis

CMOS battery leak = corrosion

As on the Williams 6809 and many boards of the era: relocate/remove the CMOS battery to avoid trace corrosion.

  • Emulation: MAME (williams/midtunit.cpp) emulates the T-Unit. No FPGA/MiSTer core (the TMS34010 is hard to reproduce in logic).

Conversions

  • ROM swaps between games on the same base (T-Unit) are possible in the collector scene; mind the sound variant (Williams ADPCM vs DCS) which differs per game.
  • No suicide encryption; the CMOS only stores settings/scores.
  • ⚠️ Do not host ROMs — method only.

EPROM repair

TMS34010 (GSP) program + ADSP/DCS sound. Program and graphics on a ROM board (mask ROM + boot EPROM). Converting = swap the game's ROM board (Mortal Kombat, NBA Jam). See MAME midway/midtunit.cpp.

Modernisation & mods

The common ground for every JAMMA board

Video, power, control panel and upscalers depend on the cabinet rather than the board: everything is centralised in Modernising a cabinet. To run the board outside a cabinet (at home, on a display): supergun.

  • Battery 🟢: a save battery is fitted (settings/counters/RTC). ⚠️ On this platform, a dead battery does NOT kill the game — it is a leaking battery that corrodes traces. Check and replace it before it leaks → save batteries.
  • Storage 🟡: the game lives in EPROM/mask ROM on the board. Changing or restoring a game means reprogramming the EPROMs (and, for a mask ROM, using a pinout adapter) → EPROM method.
  • Media preservation: replacing the original storage, multicarts, ODEs and modern options by family → PCB preservation hub.
  • Scan rate 📺: a TMS34010-based board: the screen configuration is programmed by the game in the graphics controller and does not appear in the driver — not measured here. In practice these boards stay at standard ~15 kHz. (Derived from the architecture documented above.) → tri-sync and upscalers.
  • FPGA / emulation: see the Emulation & FPGA section below.

Repair (technician)

  • TMS34010 (GSP): CPU + graphics engine — corrupt/absent image = TMS34010 / framebuffer RAM / blitter → diagnose the GSP + video RAM.
  • Sound: Williams ADPCM (M6809 + YM2151 + OKI6295) (MK1) or DCS (ADSP-2105) (NBA Jam/MK2) — a daughterboard to diagnose separately.
  • ROM board: contacts. Capacitors: recap. EPROM sockets: turned-pin socket.

→ Methods: PCB fault-finding · Recap · EPROM · Traces & vias

Photos / assets

(To add: T-Unit ROM board, TMS34010, DCS/ADPCM sound board, CMOS battery.)

Sources & attribution

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.

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