Grandstand Cosmic Invader Troubleshooting Guide
The Grandstand Cosmic Invader is VTech's 1981 Invaders game in Grandstand's name, on a Hitachi HD38750A45 microcontroller and a Futaba VFD.[1] No service information has been published for it or for VTech's and Prinztronic's versions. Two filmed repairs are the only first-hand accounts: one of a Grandstand Cosmic Invader, whose fault was a corroded battery contact,[2] and one of a VTech Sonic Invader in the same case, whose fault was a battery lead that had come off the board.[3] Opening the case is covered on Grandstand Cosmic Invader General Maintenance.
What should happen at power-on
[edit | edit source]- Switch on. The game "takes a little while to power up" before the display appears.[3]
- Before play, a number at the top of the display steps through the number of lives; the Retro Restos repairer waited for the number he wanted "before we press go". Prinztronic's version offers one to five lives.[2][3][4]
- The missile station moves only while the rocker is held over.[3]
- The difficulty switch has two positions.[1]
- To start again, switch off and on.[3]
Measurements
[edit | edit source]| Point | Expected | Source |
|---|---|---|
| Cells at the board, four fresh AA | 6.1 V was measured on the repaired Grandstand unit | [2] |
| Bench supply in place of the cells | 6 V on the battery terminals ran the Grandstand unit | [2] |
| Adaptor, if a socket is fitted | 6 V DC, 200 mA, from VTech's Sonic Invader label; polarity not recorded | [3] |
| Display supply | Not published |
Symptom checklist
[edit | edit source]
| Symptom | Likely cause | Action | Source |
|---|---|---|---|
| Dead on batteries, runs from 6 V on the battery terminals | Corroded battery contact | Clean the contacts; grind back to bright metal if needed | [2] |
| Dead on batteries, contacts clean | Battery lead off the board (the black lead on a Sonic Invader) | Check both leads; resolder | [3] |
| Dead on batteries, works with an adaptor plugged in | The socket's battery contact, which opens when a plug is inserted | Clean the socket and work a plug in and out | [3] |
| Case rattles; screws will not tighten | Screw posts broken off inside | Refix the posts | [2] |
| Display slow to appear after switching on | Normal on a working Sonic Invader | None | [3] |
| Will not change difficulty, or cuts out | Dirty slide switch | Clean the switch | [1] |
Known faults on this game
[edit | edit source]Corroded battery contact
[edit | edit source]The Grandstand unit in the Retro Restos video was sold as not working. It ran at once from 6 V applied to the battery terminals, which put the fault in the battery compartment. One contact was green with corrosion. Contact cleaner, lime juice, alcohol and brushes improved it only partly; grinding the contact back to clean metal gave 6.1 V at the board, and the game then ran on its own cells.[2] Applying 6 V to the battery terminals is a quick way to separate a compartment fault from a board fault.
Battery lead off the board
[edit | edit source]The VTech Sonic Invader in the Just4Parts video was dead. Cleaning the DC socket with contact cleaner made no difference. With the case open the cause was a black lead from the battery compartment, the negative supply, which was no longer attached to the board; black wire on black plastic made it hard to see. The repairer confirmed with a meter that the pad was ground and not the positive supply, resoldered it, and the game worked.[3]
Display faults
[edit | edit source]The display is a Futaba DM-26Z 1G, a two-colour (cyan and red) vacuum fluorescent tube, under a window with colour stripes that make some invader rows yellow and red.[1][2] The microcontroller drives it directly.[1]
| Symptom | Likely cause | Action | Source |
|---|---|---|---|
| No display and no sound | No supply: cells, contacts, leads or socket | See the symptom checklist above | [2][3] |
| Display takes a moment to appear | Normal | None | [3] |
| Some figures fainter than others | Worn phosphor; the most-lit parts fade first | Not repairable | [5] |
| One area very dim | Broken filament wire | Not repairable | [5] |
| Tube cracked or tip broken | Vacuum lost | Not repairable; a tube from another Invaders, Sonic Invader, Galactic Invaders or Cosmic Invader is the only replacement | [1][5] |
No measurements of the display supply have been published. The converter is a small ferrite-cored coil and a transistor on the board, with several small electrolytic capacitors whose values have not been published.[3] There is no capacitor guide for this game for that reason.
Things that are not faults
[edit | edit source]- The display takes a moment to light after switching on.[3]
- The invaders scroll off the display before moving down a row.[4]
- The game ends at 199 points: the counter is beaten, not broken.[4]
- The colours on the display come partly from the striped window.[2][1]
What can be repaired
[edit | edit source]| Part | Repairable? | Notes |
|---|---|---|
| Battery contacts and leads | Yes | Clean, grind back, resolder[2][3] |
| Screw posts | Yes | Heat-stake and reinforce[2] |
| Socket, switches, rocker | Yes | Clean |
| Microcontroller HD38750A45 | Only from another copy of the game | The program is in the chip; any of the four releases will do[1] |
| Display tube | Only from another copy of the game | Futaba DM-26Z 1G with this game's graphics[1] |
Because VTech's Invaders and Sonic Invader came in different cases,[6] take the chip or tube, not the whole board, from a donor of another release unless the board numbers match.
Related pages
[edit | edit source]- Grandstand Cosmic Invader
- Grandstand Cosmic Invader General Maintenance
- Grandstand Universal Mains Adaptor
- Battery Explosion, Capacitor or Corrosion Damage
References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 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.
- ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 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.
- ↑ 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 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.
- ↑ 4.0 4.1 4.2 TokyoBatman, "Prinztronic Galactic Invaders", Handheld Museum forum, 27 February 2019 (retrieved 2026-10-18): review of Prinztronic's version, "sold under 3 or more different names": two difficulty levels, a choice of one to five lives, the invaders scroll off the display before moving down, and the game is beaten at 199 points.
- ↑ 5.0 5.1 5.2 Handheld Museum forum, "EPOCH Astro Command - dead or dying", January 2016 (retrieved 2026-10-18). The site administrator (Rik): he has never had a VFD fail unless the glass was broken; with heavy use they fade unevenly, the most-lit parts first; a broken filament wire leaves an area very dim.
- ↑ Handheld Museum, "Vtech Sonic Invader" and "Vtech Invaders" (retrieved 2026-10-18): both 1981, VFD, four AA batteries; "Identical to Vtech's Invaders, just different name and case design"; also released by Grandstand as Cosmic Invader and Prinztronic as Galactic Invaders.