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Coleco Pac-Man Mini-Arcade VFD Repair

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Futaba DM-34Z VFD rear (Coleco Pac-Man Mini-Arcade)
The back of a Pac-Man's display tube, marked Futaba DM-34Z 2B, with the conductor pattern that links the graphics to the pins (photo: Rik Morgan, Handheld Museum)

The Coleco Pac-Man Mini-Arcade shows its game on a Futaba DM-34Z vacuum fluorescent display (VFD). How these tubes work, how to inspect one and how to find a bad joint are covered for all of Coleco's VFD Mini-Arcades in Coleco Mini-Arcade VFD Repair. The notes below give the Pac-Man's tube layout and drive, which tell you which connection a missing part of the picture belongs to.

The DM-34Z tube

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Pac-Man display
Item Pac-Man
Tube Futaba DM-34Z (2A in MAME's notes, 2B in the Handheld Museum teardown)[1][2]
Phosphors Cyan and red, under a colour overlay[1]
Overlay colours Orange over the playfield, pink over the lives and status area[1]
Filaments Eight, running vertically[2]
Grids Eleven: nine maze rows and two for the score area, G1 to G11 on the board[2][1]
Anode lines 26[1]

The guide's display key shows red maze walls, monsters and power capsules, yellow dots and a yellow Pac-Man, a five-digit score, a Pac-Men remaining indicator, GAME OVER and BEST legends and two score indicator arrows.[3] The overlay is a separate sheet over the glass and stays with the game if the tube is changed.[4]

How the microcontroller drives it

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The Hitachi HD38820 drives the tube directly, with no separate driver chips. It is a PMOS part of Hitachi's HMCS45A group, running from −10 V, and its outputs are rated to −50 V so that they can switch the display's grids and anodes.[5] MAME's driver connects grid lines to outputs D5 to D15 and the 26 anode lines to the R1 to R6 ports plus D1 and D2; D13 to D15 also read the skill setting and the two sticks.[1] On the 54-pin flat package the display supply enters at the pin marked Vdisp (pin 21 in MAME's pin diagram).[6]

In a multiplexed tube the matching graphics under each grid share one anode line.[7] A shape missing in the same place in every row is therefore an open anode line, and a whole row missing is an open grid line; each traces back to one pin of the HD38820.[2][1]

Faults on the Pac-Man tube

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Coleco Pac-Man Mini-Arcade VFD exhaust tip
The exhaust tip at the end of the Pac-Man tube (photo: Rik Morgan, Handheld Museum)
  • For a missing row, follow the grid from the tube pin to the HD38820. The Handheld Museum's fourth row was out because the G4 track had corroded through; a short wire soldered over the gap restored it. Only one end of some grids is connected on the board, so check which end is in use before chasing an open circuit.[2]
  • A dim vertical band means one of the eight filaments is broken. It cannot be repaired.[2]
  • If the tube is dark but the game makes sound, check the exhaust tip at the end of the tube for breakage first, then the transistors and display transformer on the board, then the pins at the two ends of the tube.[2] See Coleco Pac-Man Mini-Arcade Troubleshooting for the Pac-Man's transistors.
  • A tube wears out slowly, growing dimmer over the years, and one that has burned out has usually had too much voltage.[2] Noritake gives the evaporation of the filament's oxide coating as what limits a VFD's life.[7]

Replacing the tube

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Each Coleco game has its own tube with its graphics laid in the phosphor. MAME lists different Futaba tubes for the Pac-Man (DM-34Z) and the Ms. Pac-Man (DM-60Z), so a replacement has to come from another Pac-Man.[1][8]

  1. Remove the board as described in Coleco Mini-Arcade Maintenance.
  2. Note which way round the tube sits and keep the overlay sheet.[4]
  3. Desolder every pin completely before lifting the tube, and keep the iron and any lever away from the glass exhaust tip, the thinnest glass on the tube.[2]
  4. Fit the replacement, solder it, and check every row and the score area before closing the case.
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References

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  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 MAME source, src/mame/handheld/hh_hmcs40.cpp, driver notes for Coleco Pac-Man (cpacman, cpacmanr1): PCB label "Coleco 75690", Hitachi HD38820A28/A29 in a flat package, 1-bit sound, cyan/red Futaba DM-34Z 2A display, colour overlay, game selection with the player 1 stick, the Japanese release as Gakken's Super Puck Monster, and the note that the first version does not show the whole maze at power-on; the chip table at the head of the file. github.com/mamedev/mame.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 Rik Morgan, Handheld Museum, "Coleco Game Repair", page 3: no-power faults (supply wires, power switch, the two transistors and reverse polarity), no picture with sound (broken glass, the exhaust tip, the display supply transformer, bad joints at the display), partial display faults, the eight filaments, the nine playfield grids and two score grids, and the repair of a corroded grid trace; with photographs of the 75690 board's power section (transformer, transistors T1 and T2, zener diodes ZD1 and ZD2, two electrolytic capacitors). handheldmuseum.com. Owner's repair report.
  3. ↑ Coleco Industries, Pac-Man Instructions and Game Rules, guide no. 76879A, model no. 2390, © 1981: cover (model number, four C cells, two skill levels, one or two players); p. 2 (the three games, controls and features); p. 3 (batteries, Perma Power battery eliminator/AC adaptor #2298, weak batteries, demonstration mode and the red grid shown at switch-on); pp. 4 to 6 (Pac-Man play, display key and scoring); pp. 7 to 9 (Head to Head Pac-Man and Eat & Run); p. 10 (special information and care); p. 11 (warranty and service policy). Hosted as File:Coleco Pac-Man Mini-Arcade Instructions 76879A.pdf.
  4. ↑ 4.0 4.1 Robert Maloney, "Retro-Gaming with Coleco", HotHardware, 30 September 2004, pages 2 and 3: the Perma Power or four C cells, the inside of an opened unit, the mottling of the decals on the author's Pac-Man where the glue has seeped through ("a common issue with these units"), the Pac-Man's loud sound with no volume control, and the differences of the Ms. Pac-Man (maze variations, the moving bonus fruit, the character graphics). hothardware.com.
  5. ↑ Hitachi, Full Line Condensed Catalog (HLN1000, 1982), "4-bit Single-chip Microcomputers HMCS40 Series", pp. 105 and 106: PMOS parts have high-voltage outputs for direct drive of vacuum fluorescent displays; HMCS45A supply −10 V, power dissipation 150 mW, maximum I/O terminal voltage −50 V, ROM 2,048 × 10 bits plus 128 × 10 bits of pattern memory, RAM 160 × 4 bits, 44 I/O lines, 54-pin flat package. bitsavers.org.
  6. ↑ MAME source, src/devices/cpu/hmcs40/hmcs40.cpp and hmcs40.h: the HD38820 is the PMOS member of the HMCS45 group, in a 54-pin flat package or 64-pin DIP, with 44 I/O lines, (2,048 + 128) × 10-bit ROM and 160 × 4-bit RAM; pin diagram of the 54-pin package. github.com/mamedev/mame.
  7. ↑ 7.0 7.1 Noritake Itron, "A Guide to Fundamental VFD Operation" (revised July 2001): VFD construction (filament cathode, grids, phosphor anodes, getter, evacuation tube), multiplexed drive, filament supply and centre-tapped DC-to-AC converters for battery equipment, cut-off bias, and the dependence of brightness and life on filament voltage. noritake-elec.com.
  8. ↑ MAME source, src/mame/handheld/hh_hmcs40.cpp, driver notes for Coleco Ms. Pac-Man (cmspacmn): made in Taiwan under licence from Midway; PCB label "Coleco 911171"; Hitachi HD38820A61 in a flat package; 1-bit sound; cyan/red Futaba DM-60Z 3I display; colour overlay (lives and playfield orange, best score pink, fruit yellow); game selection with the player 1 stick; port mapping. github.com/mamedev/mame.


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