Coleco Zaxxon Mini-Arcade VFD Repair
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The Coleco Zaxxon Mini-Arcade builds its picture from two vacuum fluorescent display (VFD) tubes and a part-reflecting mirror sheet.[1][2] A VFD is a vacuum triode: heated filaments give off electrons, grids switch them on and off, and phosphor-coated anodes glow where the electrons land. In a multiplexed tube the matching anode segments under each grid share one connection.[3] The general method for Coleco's single-tube Mini-Arcades is on Coleco Mini-Arcade VFD Repair.
Warning: the board makes a high voltage for the tubes. Rik Morgan notes that on Coleco's VFD games it can give a mild shock; keep fingers off the tube pins and the supply section while the game is on.[4]
The two tubes and the mirror
[edit | edit source]| Item | Large tube | Small tube |
|---|---|---|
| Mounting | Black plastic holder screwed to the main board[2][5] | Black plastic holder on a separate board behind the mirror[2][5] |
| Tint over the glass | Magenta[2] | Orange[2] |
| Segments seen in the unlit tube | Walls, ground targets and score digits[2] | Rows of fighter shapes[2] |
| Retrofixes' caption | "the background effects and enemy ships"[2] | "the Flying Zaxxon ship"[2] |
| How the player sees it | Reflected in the mirror[2] | Through the mirror[2] |
The Handheld Museum describes the player's ship and airborne enemies as coming from the tube reflected in the mirror.[1] Retrofixes' annotated side view shows the large tube reflected and the small one seen through the glass, and its photographs put the fighter shapes on the small tube.[2] The part numbers of the two tubes have not been published.
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The mirror is a tinted sheet that stands upright between the two display boards. It is usually glued in and breaks easily.[2]
How the tubes are driven
[edit | edit source]MAME's list of Hitachi mask numbers gives the game's microcontroller as an HD38820A62, a PMOS part of Hitachi's HMCS45 group; its program has not been dumped.[6][7] Hitachi gave its PMOS microcontrollers 50 V outputs for driving vacuum fluorescent displays directly and specified them for a −10 V supply.[8] No schematic of the game has been published, so which grid and anode lines go to which tube is not known. Battery-powered VFD equipment generally runs the filaments from a DC-to-AC converter, and filament voltage sets both brightness and tube life.[3]
Testing the tubes
[edit | edit source]Hold the stick in any direction while switching on to run the graphics test, or hold a fire button to run the test followed by the demonstration.[1] Watch both tubes; each carries its own set of shapes, so check them one at a time.
| Symptom | Probable cause | Action |
|---|---|---|
| Picture dim or hazy, both tubes | Dust on the mirror and the tube faces | Clean the mirror and both tubes with glass cleaner on a microfibre cloth.[2] |
| Picture dim on one tube after cleaning | Worn tube, or low filament supply | Fit fresh cells. A VFD wears out slowly, growing dimmer over the years.[4][3] |
| One tube dark | Broken glass or exhaust tip, or a bad joint at that tube | Inspect the glass and the exhaust tip, then press gently on the tube and flex the board slightly while watching it.[4] |
| One shape missing everywhere it appears | Open anode line | Follow the line from the tube pin to the board and check the joint and the track.[3][4] |
| A whole section of a tube dark | Open grid line | Check the grid pin's joint and track the same way.[3][4] |
| Shapes flicker in and out | Cracked solder joint at the tube or the microcontroller | Reflow the joints.[4] |
Inspecting a tube
[edit | edit source]- Open the case as described on Coleco Zaxxon Mini-Arcade Maintenance, taking care of the mirror.[2]
- Look for loose pieces of glass in the case. A VFD is a sealed vacuum envelope, and any hole in it ends the tube's life.[4]
- Inspect the exhaust tip on each tube, the small glass nipple where the air was pumped out during manufacture. It is the thinnest and weakest glass on the tube.[4][3]
- Look for brown burnt areas near the pins. A tube burnt like this is unlikely to be repairable.[9]
- A dark or silvery mark about half an inch across inside the glass is normal.[4]
- With the game on, press very gently on the tube and its holder and watch for segments that flicker on. Reflowing all of that tube's joints is usually quicker than finding the single bad one.[4]
Replacing a tube
[edit | edit source]Each tube carries the Zaxxon's own graphics in its phosphor, so a replacement has to come from another Coleco Zaxxon.[2] Bandai's Zaxxon tabletop has a single tube divided between a direct and a reflected view, a different part altogether.[10]
- Photograph the tube, its holder and the mirror before moving anything.
- Remove the screws that hold the tube's plastic holder to its board.[2]
- Desolder every pin completely before lifting the tube, and keep the iron and any lever away from the exhaust tip.[4]
- Fit the replacement the same way round, solder it, and run the graphics test before refitting the mirror and the case.[1]
Related pages
[edit | edit source]- Coleco Zaxxon Mini-Arcade
- Coleco Zaxxon Mini-Arcade Troubleshooting
- Coleco Zaxxon Mini-Arcade Maintenance
- Coleco Zaxxon Mini-Arcade Capacitor Replacement Guide
- Coleco Mini-Arcade VFD Repair
References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 Rik Morgan, Handheld Museum, "Coleco Zaxxon": 1983, two VFDs, four D batteries, model 2396; mirrors and two VFDs give the 3-D effect, with the player's ship appearing to fly over the walls; the planet surface and ground enemies on one VFD and the player's ship and airborne enemies on the VFD reflected off a mirror; a true eight-way joystick with eight metal contacts round the stick; one of the largest games on the site and heavy on four D cells; games seen for sale with the stick handle missing, leaving a short straight stick; holding the fire button while switching on runs a graphics test and then a demonstration, holding the stick runs the graphics test only; the author's game is the Canadian version, photographed boxed and in play. handheldmuseum.com. Collector's notes.
- ↑ 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 Retrofixes, "Restoring Zaxxon TableTop Mini Arcades", November 2014: two VFDs and a mirror; original price $60, released 1983; six screws on the underside; corroded battery contacts cleaned with vinegar and cotton buds, with light sandpaper for the worst cases; separating the two halves slowly because of the mirror inside; cleaning the tubes makes a large difference to play; one tube reflects off the mirror and the other is seen through it (annotated photograph); cleaning the mirror gently with Windex and a microfibre cloth; the mirror is usually glued in and is fragile; captions saying that one tube "creates the Flying Zaxxon ship" and the other "the background effects and enemy ships"; cleaning the stick and buttons with alcohol or electrical cleaner on a swab; re-fixing peeling decals with paper cement; polishing the case with Novus No. 1 without soaking the decals; 19 photographs. retrofixes.blogspot.com. Owner's restoration report.
- ↑ 3.0 3.1 3.2 3.3 3.4 3.5 Noritake Itron, "A Guide to Fundamental VFD Operation": a VFD is a triode with filament cathodes, control grids and phosphor-coated anodes; in multiplexed tubes the matching anode segments under each grid share one data line; VFD life is set by evaporation of the filament's oxide coating, so the filament voltage must stay within its rating; battery equipment drives the filament from a DC-to-AC converter; the evacuation tube is part of the glass envelope. noritake-elec.com.
- ↑ 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 Rik Morgan, Handheld Museum, "Coleco Game Repair (Pac Man, Ms. Pac Man, Donkey Kong, Frogger & Galaxian)", page 3: written for Coleco's single-tube games, with the note that much of it applies to VFD games in general; no power (check the voltage where the battery wires meet the board and through the power switch; a transistor that gets hot within seconds; transistors damaged by reversed power); no picture with sound (loose glass, the exhaust tip as the thinnest and weakest glass on a VFD, the high-voltage supply from a transformer that can give a mild shock, bad joints found by gently flexing the board while watching the display); tubes that dim slowly with age; a dark or silvery mark about half an inch across inside the tube is normal; partial displays usually from a bad solder joint at the tube or the microcontroller. handheldmuseum.com. Owner's repair notes.
- ↑ 5.0 5.1 Rik Morgan, Handheld Museum, "Game Guts!": photograph of an opened Coleco Zaxxon, captioned "Notice the two VFD displays seperated by a mirror". handheldmuseum.com.
- ↑ MAME source,
src/mame/handheld/hh_hmcs40.cpp: the list of Hitachi HMCS40 mask numbers at the head of the file gives "A62 HD38820 1983, Coleco Zaxxon", marked as not dumped; the driver notes for Bandai Zaxxon (HD38800B19, one NEC FIP11BM24T tube, half of it reflected with a one-way mirror). github.com/mamedev/mame. - ↑ MAME source,
src/devices/cpu/hmcs40/hmcs40.cppandhmcs40.h: the HD38820 is the PMOS member of Hitachi's 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. github.com/mamedev/mame. - ↑ Hitachi, Full Line Condensed Catalog (1982), "4-bit Single-chip Microcomputers HMCS40 Series", pp. 104 to 106: the PMOS parts run from −10 V and have 50 V outputs "for direct vacuum fluorescent drive". bitsavers.org.
- ↑ Steven Read, Mini-Arcade, "How to fix a handheld game": dirty contacts as the cause of a stick or button that needs hard pressing, moves two or three steps, or hesitates; cleaning contacts with a pencil eraser and alcohol; on VFD tabletops that use C or D cells, corrosion can build up on the terminals within weeks if the batteries are left in; checking for fresh batteries before deciding a game is faulty; looking for cracks or burnt areas on a VFD that does not light. miniarcade.com.
- ↑ Rik Morgan, Handheld Museum, "Bandai Zaxxon": CPU Hitachi HD38800-B19, four C batteries; one VFD split in two, half of it reflected in a semi-transparent mirror, "unlike Coleco's Zaxxon which uses two"; on the Bandai game all the ships have depth, "not just the player's ship like on the Coleco version". handheldmuseum.com.