Coleco Mini-Arcade VFD Repair
Each of Coleco's VFD Mini-Arcade tabletops has its own vacuum fluorescent display (VFD), with that game's graphics laid down in the phosphor, so a replacement tube has to come from another unit of the same game.[1][2] The display, its supply and its joints are dealt with here for Pac-Man, Galaxian, Frogger, Donkey Kong and Ms. Pac-Man. Opening the case is on Coleco Mini-Arcade Maintenance, and the general symptom list on Coleco Mini-Arcade Troubleshooting.
How the display works
[edit | edit source]A VFD is a vacuum tube with three kinds of electrode. Fine tungsten filaments coated with oxide are the cathode and give off electrons when heated. A wire-mesh grid passes the electrons when it is positive and blocks them when it is negative. The anodes carry the phosphor of each segment, which lights when the anode is positive and electrons reach it. In a multiplexed display the anodes under each grid are connected in common, and the grids are switched on in turn fast enough that the display does not flicker.[3]
The Handheld Museum's description of the Pac-Man tube matches this. Looking through the score area, eight thin vertical filament wires can be seen; they run the full height of the display. Each row of the playfield is under one grid, nine in all, and the score digits sit under grids of their own. The back of the glass carries the conductive pattern that reaches every graphic. The graphics are grouped, so a game with around a hundred of them may need only 15 to 20 connections. The tube is a Futaba part.[2]
In these games the microcontroller drives the grid and anode lines itself; MAME's drivers connect its output ports straight to the display.[1][4] Hitachi built its PMOS 4-bit microcontrollers, which include the HD38800 (HMCS44A) and HD38820 (HMCS45A) used by Coleco, with high-voltage outputs for this purpose. They run from −10 V and their I/O pins are rated to −50 V.[5]
| Game | Display | Colours | Grid lines | Anode lines | Microcontroller |
|---|---|---|---|---|---|
| Galaxian | Futaba DM-36Z 2H | Cyan and red | 12 | 14, plus corner segments switched by the player switch | Hitachi HD38800A70 |
| Frogger | Itron CP5090GLR R1B | Cyan, red and green | 12 | 16 | Mitsubishi M58846-701P |
| Donkey Kong | Futaba DM-47ZK 2K | Cyan and red | 11 | 28 | Hitachi HD38820A45 |
| Pac-Man | Futaba DM-34Z 2A (2B also seen) | Cyan and red | 11 | 26 | Hitachi HD38820A28 or A29[6][2] |
| Ms. Pac-Man | Futaba DM-60Z 3I | Cyan and red | 11 | 26 | Hitachi HD38820A61[6] |
A colour overlay over the tube adds further colours: red over the Donkey Kong playfield, orange and pink on Galaxian, blue and yellow bands on Frogger.[1][4]
The display supply
[edit | edit source]The display needs a higher voltage than the four C cells give. It comes from a small transformer on the main board, driven by a transistor.[2][7] Noritake's guide describes the same arrangement for battery equipment: a DC-to-AC converter supplies the filament.[3]
- Two styles of transformer were used: a small wound transformer on the first Pac-Man board, and a large round black one on the Pac-Man Rev. E board.[2][8]
- A working transformer usually makes a faint high-pitched whine. The Handheld Museum's author had never found a failed one.[2]
- The transistors fail more often, usually after reverse polarity, and a failed one can get hot within seconds of switching on. Test them out of circuit.[2]
- A missing switching transistor on a Pac-Man was replaced with a TIP41C NPN power transistor, and the display worked again.[7]
- The supply gives a mild shock if touched with the game on.[2]
Noritake notes that the life of a VFD is set by the evaporation of the oxide coating from the filaments, so the filament voltage has to stay within its rating.[3] The Handheld Museum's experience is the same: tubes fade slowly over the years, and a tube that has burned out has usually had too much voltage.[2] Measure any replacement supply before using it; four alkaline C cells give about 6 V.[9]
Inspecting the tube
[edit | edit source]
- Look for glass fragments in the case and for cracks at the corners of the tube.[2]
- Check the exhaust tip, the small glass nipple through which the tube was evacuated. It is the thinnest glass on the tube and the easiest to snap. Any hole in the envelope destroys the display.[2]
- Ignore a black or silvery mark about half an inch across inside the tube. It is normal.[2]
- With the game running, look along the display for a vertical strip that is slightly dimmer than the rest. That is a broken filament; more broken filaments leave more of the display dark.[2]
Finding a bad joint
[edit | edit source]A display that is completely dark with sound present, or that has a row or block missing, usually has a bad joint at the display pins or at the microcontroller.[2]
- With the game running, push the display very gently to the left and to the right, lift it a little and press it down, and put light bending pressure on the board without actually bending it. Watch the display throughout.[2]
- If any part of the display comes on, even for an instant, there is a bad contact. It is quicker to reheat and re-flux every display pin than to find the one joint.[2]
- A completely dead display is usually down to one of the first two or last two pins on each side.[2]
- If pressure changes nothing, follow the grid line for the missing row from the display pin to the microcontroller. A torch behind the board shows the traces on both sides. Some grid lines leave the tube at both ends, and only one end is connected on the board.[2]
- Look for corrosion along the trace. On the Handheld Museum's Pac-Man the copper of the G4 line had corroded right through; scraping the area clean showed the gap, and a short wire soldered across it brought the row back. Clean and bridge any other discoloured traces at the same time.[2]
A KLOV member asked whether one missing vertical row on a Ms. Pac-Man was a cold joint at the display; another replied that reflowing the display joints had cured missing lines on a Frogger.[10]
Model notes
[edit | edit source]Galaxian
[edit | edit source]The two-player position of the power switch enables the corner segments of the Galaxian display directly, not through the microcontroller.[1]
Frogger
[edit | edit source]Frogger's tube is an Itron part on a board made in Japan, where the other games use Futaba tubes on boards made in Taiwan.[4][1] Konami's own Frogger, sold by Gakken, uses an M58846-700P microcontroller on a different board.[4]
Donkey Kong
[edit | edit source]Donkey Kong's Futaba DM-47ZK 2K has 11 grids and 28 anode lines, the most of the three. Its overlay puts one shade of red over the playfield and a second over Donkey Kong and the princess.[1]
Pac-Man
[edit | edit source]The Pac-Man's DM-34Z has eight filaments and eleven grids, nine for the rows of the maze and two for the score area, labelled G1 to G11 on the board.[2] MAME's driver puts the grids on outputs D5 to D15 of the HD38820 and also reads the skill setting and both sticks on D13 to D15.[6] Tube layout, drive lines and replacement: Coleco Pac-Man Mini-Arcade VFD Repair.
Ms. Pac-Man
[edit | edit source]The Ms. Pac-Man uses a different tube, the Futaba DM-60Z 3I, with the same eleven grid and 26 anode lines as the Pac-Man, so the two tubes are not interchangeable.[6] See Coleco Ms. Pac-Man Mini-Arcade VFD Repair.
Related pages
[edit | edit source]References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 MAME source, hh_hmcs40.cpp (retrieved 2026-10-06), driver notes and port mapping for Coleco Donkey Kong (Futaba DM-47ZK 2K, cyan and red; grid on D4–D14, plates on R0x–R6x; overlay colours) and Coleco Galaxian (Futaba DM-36Z 2H, cyan and red; grid on R1x–R3x, plates on D2–D15; the two-player switch enables the corner segments directly; overlay colours). Emulator documentation written from real boards.
- ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 2.12 2.13 2.14 2.15 2.16 2.17 2.18 2.19 Handheld Museum, "Coleco Game Repair (Pac Man, Ms. Pac Man, Donkey Kong, Frogger & Galaxian)", page 3 (retrieved 2026-10-06). Community repair guide written on a Pac-Man: display construction (filaments, grids, the exhaust tip, the normal burn mark), the high-voltage transformer and its whine, display joints, gradual dimming, damage from too much voltage, and the trace repair on the G4 grid line.
- ↑ 3.0 3.1 3.2 Noritake Co., "A Guide to Fundamental VFD Operation", revised 28 July 2001 (retrieved 2026-10-06): electrodes, multiplex drive, filament supply from a DC-to-AC converter in battery equipment, and filament life set by evaporation of the oxide coating.
- ↑ 4.0 4.1 4.2 4.3 MAME source, hh_melps4.cpp (retrieved 2026-10-06), driver notes and port mapping for Coleco Frogger (Itron CP5090GLR R1B, cyan, red and green; grid on D0–D11, plates on ports S, F and G; overlay colours; Mitsubishi M58846-701P).
- ↑ 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; HMCS44A and HMCS45A run from −10 V with a maximum I/O terminal voltage of −50 V. bitsavers.org.
- ↑ 6.0 6.1 6.2 6.3 MAME source, hh_hmcs40.cpp (retrieved 2026-10-06), driver notes and port mapping for Coleco Pac-Man (Futaba DM-34Z 2A, cyan and red; grid on D5–D15, plates on R1x–R6x, D1 and D2; overlay orange and pink; Hitachi HD38820A28/A29) and Coleco Ms. Pac-Man (Futaba DM-60Z 3I, cyan and red; grid on D5–D15, plates on R1x–R6x, D0 and D1; overlay orange, pink and yellow; Hitachi HD38820A61).
- ↑ 7.0 7.1 KLOV forums, "PACMAN Coleco repair : component information", August–September 2011 (retrieved 2026-10-06). Community thread: a Pac-Man with the switching transistor missing; the owner traced it as the switching transistor of the supply working with the transformer and fitted a TIP41C NPN transistor, after which the game worked.
- ↑ Handheld Museum, "Circuit Board variations" (retrieved 2026-10-06): a Pac-Man board marked Rev. E with the large round transformer and the transistors moved.
- ↑ Coleco Industries, Donkey Kong Instructions and Game Rules, Guide No. 78247, 1982, p. 3: four C alkaline cells or the Perma Power battery eliminator. Hosted here as File:Coleco Donkey Kong Tabletop Instructions Guide 78247.pdf.
- ↑ KLOV forums, "Coleco handheld arcade games - anyone fix those or have intel on them?", April–May 2022 (retrieved 2026-10-06). Community thread: a Ms. Pac-Man with one vertical row missing, suspected cold joint; a Frogger with missing lines fixed by reflowing the display joints.