Grandstand Cosmic Invader General Maintenance
Grandstand Cosmic Invader is VTech's Invaders game in Grandstand's name, sold in the UK from 1981. VTech also sold it as Invaders and Sonic Invader, and Prinztronic as Galactic Invaders.[1][2] It is a long, narrow yellow case with a black base, a vacuum fluorescent display under a striped colour window, a rocker joystick and a red fire button, and it runs on four AA cells.[2][3] No leaflet, manual or schematic for any of the four releases has been found, and no freely licensed photograph of the game is known. The advice here comes from MAME's notes on the hardware, a filmed repair of a Grandstand unit, and a filmed repair of VTech's Sonic Invader, whose board carries the same 700255 number.[3][4] Faults are covered on Grandstand Cosmic Invader Troubleshooting Guide.
The Cosmic Invader at a glance
[edit | edit source]| Part | Detail | Source |
|---|---|---|
| Board | One board printed 700255F and 35-0155-00 on the Grandstand unit (700255 G and 35-0155-01 on a Sonic Invader) | [3][4] |
| Microcontroller | Hitachi HD38750A45 (HMCS40 family), made in Japan, with the game in its own ROM | [1][4] |
| Display | Futaba DM-26Z 1G vacuum fluorescent tube, cyan and red, mounted on the board; colour stripes on the window add the zone colours | [1][3] |
| Display supply | A small round ferrite-cored converter coil and a small transistor on the board, with several small electrolytic capacitors | [4] |
| Controls | Rocker joystick (left and right) on a small sub-board, red fire button, power switch and two-position difficulty switch | [1][3][4] |
| Sound | Piezo disc on two leads, over the battery compartment | [3][4] |
| Power | Four AA cells in the base; VTech's label allows a 6 V, 200 mA adaptor, and the Sonic Invader has its socket on the side of the case | [2][4] |
Before you start
[edit | edit source]- Switch off and take the four AA cells out.
- Tools: a small cross-head screwdriver, isopropyl alcohol, a soft brush, contact cleaner, a fibreglass pen or fine abrasive for the battery contacts, and a multimeter.
- The game runs from 6 V,[3] and a converter coil on the board makes the higher voltages a vacuum fluorescent display needs.[4] Keep fingers off the coil and its neighbours while the board is powered.
- If an old adaptor is to be used, inspect its case and lead first; see Grandstand Universal Mains Adaptor.
Opening the case
[edit | edit source]From the two filmed repairs:[3][4]
- Take out the cells.
- Remove the screws from the base: on the Sonic Invader, two cross-head screws inside the battery compartment and two at the other end. There are no clips.
- Lift the yellow top off. Hold the case level as you do: the knobs of the slide switches can fall out.
- The board is held to the black base by six small screws, with the display tube mounted on it. The piezo speaker sits over the battery compartment at one end, on two leads.
- Before turning the board over, note the red and black leads from the battery compartment. On the Sonic Invader the black lead was found detached from the board; its repairer thought it might have come off when he turned the board over.[4]
Broken screw posts
[edit | edit source]On the Grandstand unit in the Retro Restos video, two base screws were missing because their posts had broken off inside the case, and the loose posts rattled. Superglue would not hold on this plastic; the repairer fixed the posts back in place by melting them in with a soldering iron, then built them up with hot glue.[3] Check that every post bites before tightening the screws fully.
The display tube
[edit | edit source]The tube is a Futaba DM-26Z 1G mounted on the board.[1] Its sealed glass tip, where the air was drawn out, is at one end.[4] Do not lay the board face down on the tube or press on the tip; a tube that has let air in cannot be repaired, and the only replacement is a tube from another copy of the game, whichever company's name is on it.
Cleaning
[edit | edit source]- The yellow top and black base can be washed in warm soapy water with the board out.
- The colour stripes are on the window; clean it with a damp cloth only.[3]
- Scratches and marks on the case can be polished out with wet-and-dry paper and cutting compound; the Retro Restos repairer cut out and sanded down a deep cigarette burn this way, accepting that it would never be invisible.[3]
- Clean the board with isopropyl alcohol and a soft brush.
Batteries and the battery contacts
[edit | edit source]- Four AA cells.[2]
- The contacts in the base corrode green if cells are left in. On the Grandstand unit one contact was so corroded that contact cleaner, lime juice and alcohol were not enough, and it had to be ground back to bright metal before the cells gave 6.1 V at the board. The repairer noted that a contact ground back like this would ideally be re-plated.[3]
- Check the red and black leads where they leave the battery compartment and where they join the board.[4]
- Take the cells out for storage; see Battery Explosion, Capacitor or Corrosion Damage.
The adaptor socket
[edit | edit source]
VTech's Sonic Invader label reads "Operates on 4 'AA' batteries or a 6 volts/200 MA AC adaptor"; despite the wording, four AA cells give 6 V DC, and the socket is a DC input.[4] On the Sonic Invader the socket is mounted on the board and comes out through a boss on the side of the case near the display end.[4] The published film of a Grandstand unit does not show the side of the case clearly enough to confirm the same socket, though the board is the same 700255 design.[3]
- The socket disconnects the cells when a plug is inserted, and a dirty socket can leave the game dead on batteries. Spray contact cleaner in and work a plug in and out.[4]
- No polarity is printed on the parts of the label that have been photographed. Measure how the socket's contacts connect to the battery leads before connecting any adaptor.
Controls
[edit | edit source]- The joystick is a rocker switch on a small sub-board, returned by two springs. The Retro Restos repairer judged it sturdier than the small spring-and-ball joysticks of Astro Wars and CGL's Galaxy Invader, which wear out.[3]
- The missile station moves only while the rocker is held over.[4]
- The fire button and the two white slide switches sit on the board.[3] Clean the slide switches with contact cleaner if the game will not switch on reliably or change difficulty.[1][4]
Wearing parts
[edit | edit source]| Part | What happens | Check |
|---|---|---|
| Battery contacts | Green corrosion, poor contact[3] | Clean; grind back if needed |
| Battery leads to the board | Black lead found detached on a Sonic Invader[4] | Resolder |
| Screw posts in the case | Break off inside[3] | Refix with heat and hot glue |
| Adaptor socket | Dirty contacts[4] | Clean |
| Front label | Peels[4] | Refix with thin double-sided tape |
Storage
[edit | edit source]- Remove the cells.
- Keep it dry and out of the sun, lying flat.
Preventive maintenance checklist
[edit | edit source]- Take out the cells and clean the contacts.
- Open the case and check both battery leads at the board.
- Check every screw post holds its screw.
- Clean the socket, the slide switches and the rocker.
- Reassemble, then check the lives selection, both difficulty settings and the fire button.
Related pages
[edit | edit source]- Grandstand Cosmic Invader
- Grandstand Cosmic Invader Troubleshooting Guide
- Grandstand Universal Mains Adaptor
- Grandstand Invader From Space, Epoch's invader game for Grandstand, on different hardware
- Battery Explosion, Capacitor or Corrosion Damage
References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 MAME source, hh_hmcs40.cpp at commit d404316 (retrieved 2026-10-18). Driver notes for VTech Invaders: "manufactured in Taiwan"; Hitachi HD38750A45 microcontroller, 1-bit sound; cyan and red VFD Futaba DM-26Z 1G; colour overlay on the alien rows; known releases Invaders and Sonic Invader (VTech, USA), Cosmic Invader (Grandstand, UK) and Galactic Invaders (Prinztronic, UK); inputs left, right and fire, and a two-position difficulty switch. The chip list dates the HD38750A45 to 1981; the program is dumped from the microcontroller itself.
- ↑ 2.0 2.1 2.2 2.3 Handheld Museum, "Grandstand Cosmic Invader" (retrieved 2026-10-18): 1981, VFD, four AA batteries; "Licensed from Vtech, it's identical to Vtech's Sonic Invader"; also released by Prinztronic as Galactic Invaders. The photographs, examined: a long, narrow yellow case with "GRANDSTAND COSMIC INVADER" on a raised name block above the display; the display window labelled Score, UFO Zone, Invader Zone, Ground and Missile Station, with row numbers; a square joystick and a red fire button below it; a black slide switch near each lower corner; the box ("Exciting 'arcade-like' action ELECTRONIC GAME").
- ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 3.11 3.12 3.13 3.14 3.15 3.16 retro_ restos, "Grandstand Cosmic Invader 1980's Game eBay 'Untested' Repair", YouTube, 20 December 2024 (transcript read and the 720p video examined frame by frame, retrieved 2026-10-18). A dirty Grandstand unit sold as not working, rattling, with a burn on the case top: two base screws missing and their screw posts broken off inside, which was the rattle; the battery contacts green with corrosion; the top case "comes away totally"; inside, colour stripes on the window, the piezo speaker, the display, and a joystick that is a rocker switch with two springs; the game ran from 6 V on the battery terminals; before play "we wait for the number of lives that we want before we press go"; the corroded contact was cleaned with contact cleaner, lime juice and alcohol, then ground back to clean metal, after which the cells gave 6.1 V at the board and the game worked on batteries; the broken posts were fixed back with a soldering iron (superglue would not hold on this plastic) and reinforced with hot glue; the burn was cut back and sanded. Frames examined show the black base with the battery compartment at one end and a torn "GRANDSTAND COSMIC INVADER" label; the green board printed "700255F" and "35-0155-00", with the display tube mounted on it, the red fire button, the red rocker of the joystick on a small sub-board and a white slide switch at each side of that end; the piezo disc on green leads over the battery compartment; and red and black leads from the battery compartment to the board.
- ↑ 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 4.11 4.12 4.13 4.14 4.15 4.16 4.17 4.18 4.19 4.20 Just4Parts, "Can I Fix This Broken Vintage Space Invaders Handheld? Sonic Invaders Repair!", YouTube, 7 August 2026 (transcript read and the 720p video examined frame by frame, retrieved 2026-10-18). A dead VTech Sonic Invader in the same case as Grandstand's Cosmic Invader. Frames examined: the base label "Operates on 4 'AA' batteries or a 6 volts/200 MA AC adaptor" (also in French, German and Italian); a DC socket in a boss on the side of the case near the display end; the board printed "700255 G" and "35-0155-01", with the display tube's sealed glass bulb at one end; on its other side a Hitachi microcontroller marked "HD38750A45", "1F45" and "JAPAN", a small round ferrite-cored converter coil, a small transistor, several small electrolytic capacitors (values not legible) and the board-mounted DC socket. From the transcript: the base says it was made in 1981 in Hong Kong; contact cleaner in the socket did not help; two cross-head screws in the battery compartment and two at the bottom hold the case, with no clips; the slide switches' knobs can fall off when the top is lifted; six screws hold the board; the fault was the black negative lead from the battery compartment, which had come off the board; with it resoldered the game worked; it "takes a little while to power up"; the number of lives is chosen at the start and shown at the top of the display; a difficulty switch on the side; the game is reset by switching off and on; a peeling front label was refixed with double-sided tape.