Grandstand Firefox F-7 Troubleshooting Guide
Fault-finding for the Grandstand Firefox F-7 and the identical Epoch Astro Thunder 7 and Radio Shack Astro Thunder.[1] No manufacturer's service data has been found. An owner, Philip Bryden, drew a schematic of the game in 2022 from his own boards, and seven channels have published repairs on video; the faults and readings below come from them, with the operating details from Grandstand's and Radio Shack's leaflets.[2][3][4] Opening the case is described on Grandstand Firefox F-7 General Maintenance.
How the electronics work
[edit | edit source]Bryden's schematic shows an NEC D7528C microcontroller (labelled D7528C 011) driving the display, a second NEC chip labelled D1771C 011, and a 5 MHz ceramic resonator, X01 (FCR5.0M).[2] Bryden traced the large speaker's wires to the second chip, and Retro Tech Repair believed it makes the more complex sounds while the main processor drives the small speaker.[5][6] As on the other Epoch games, a power transistor drives a small transformer to make the display's supplies: here the D882 is S04, its base driven by S03, a C945, and the transformer is marked TX-30, with ten pins.[2][5] The cells or adaptor feed 6 V through the power switch on the control board and pin 4 of the ten-way cable to the main board.[2][5]
What should happen at power-on
[edit | edit source]- POWER on: an electronic tune plays and the display lights, with skill level 1 shown at the top right.[3]
- SELECT steps through three skill levels; START plays a tune and begins the game.[3]
- The joystick moves the ship left and right; pushed up or down it shows H or L for a few seconds of high or low speed.[3]
- Each speaker sounds only if its switch is on: the left one plays the music, the right one the sound effects.[3][4]
Expected measurements
[edit | edit source]| Point | Reading | Source |
|---|---|---|
| Supply into the board (ribbon pin 4) | About 6 V | [5][2] |
| Current at 6 V with a new D882 | About 300-390 mA on one game, which Bryden considered about right | [5] |
| Current, dead game with a failed D882 | Nothing | [5] |
| Current with a transistor fitted backwards, or a solder bridge | High; 0.8 A on one game | [5][6] |
| Firing button pad, good | About 15-45 kΩ across the pad (one meter, one game) | [7] |
| Firing button pad, worn | About 240 kΩ | [7] |
No internal supply voltages have been published for this game.
Symptoms
[edit | edit source]| Symptom | Likely cause | Action | Source |
|---|---|---|---|
| Dead on cells and adaptor; 6 V reaches the board | Failed D882 power transistor | Test it out of circuit; replace it. | [8][6][5][9] |
| Dead on cells and adaptor; nothing reaches the board | Oxidised battery contacts and a dirty DC socket | Clean the contacts and socket. | [10] |
| Dead after a knock or a previous repair | A cracked screw post has cracked the board and broken a track | Look for cracks near the posts; bridge the track with wire. | [7] |
| Supply goes into current limiting; nothing gets hot that can be found | A short in the power section; on one game it cleared only when the transformer was removed | Lift parts one at a time; see Transformer. | [11] |
| A new D882 runs very hot | Fitted the wrong way round, or failed again | Check the orientation against the board; test the C945 driver. | [5] |
| Still faulty after the power section has been repaired and the supplies are good | Failed microcontroller (found on two games) | Swap the chip with a known-good game to prove it; donor part only. | [12] |
| No sound | Both speaker switches off | Switch them on. | [3][5] |
| Only one speaker plays | Normal: they play different sounds; or a broken speaker wire | Check both switches and the wires. | [10][6] |
| Quiet sound, sound chip running hot, high current | Solder bridge between two tracks at a connector | Inspect the connectors for bridges. | [6] |
| Sound cuts in and out; joystick will not go right | Broken conductor in the ten-way cable between the boards | Replace the cable with wire. | [5] |
| Ship will not move right, cable good | Dirty joystick contacts or pads | Clean with isopropyl alcohol. | [10] |
| Firing button unresponsive | Worn carbon pad | Swap with the select pad. | [7][6] |
| Display erratic, game malfunctions | Weak cells | Fit fresh cells. | [3][4] |
Known faults
[edit | edit source]D882 power transistor
[edit | edit source]The power transistor was the fault on most of the dead games: it read short between two pins for Retro Tech Repair in 2019, as "two resistors" for him in 2021, and was visibly burnt, with a mark on the board, for 8Bit Retro ReFix.[8][6][9] A new or salvaged D882 cured Retro Tech Repair's games; one salvaged part was itself faulty.[8][6] Bryden's first replacement also failed and a second was needed, after a substitute fitted backwards had drawn 0.8 A.[5] 8Bit Retro ReFix put the failure down to a reversed adaptor; that is his belief, not a finding.[9]
Microcontroller
[edit | edit source]Bryden's two Firefox F-7s both had faulty microcontrollers. He spent hours on the supply rail and parts before swapping the chips between the games proved it; with no replacement chips available, neither could be repaired.[12] He found no source of replacement chips, so a scrapped Firefox F-7 or Astro Thunder is the only likely source.[12][1]
Transformer
[edit | edit source]Repairing Faulty Tech's game held its bench supply in current limiting until the transformer was taken out. The transformer looked intact under a microscope; he suspected an internal short between windings and stopped there, expecting no replacement to be found.[11] Bryden tested his transformer's ten pins and found nothing wrong; his fault was the D882.[5] The board carries a mark and the transformer an arrow, to refit it the right way round.[5]
The ten-way cable
[edit | edit source]Bryden's game had intermittent sound and a joystick that would not go right. Feeding the speaker directly from the far end of the cable proved the cable faulty; he replaced it with ten separate wires, in the end from an old IDE cable because thinner wire kept snapping.[5]
Sound
[edit | edit source]Retro Tech Repair's game was quiet, its sound chip ran very hot and the current at switch-on was high. A chip from a spare board did the same, and recapping the two supply capacitors made no difference. The cause was a solder bridge between two tracks on a badly soldered connector, one of them to the speaker; with it removed the sound was louder, the current lower and the chip cool.[6] Bryden's game was still missing its in-game effects at the end of his first video, with the music working; he suspected the sound chip or X01.[5]
Capacitors
[edit | edit source]No capacitor has been found to cause a fault on this game. Repairing Faulty Tech measured C07 (472K, 4.7 nF) and C10 (473Z, 47 nF) in tolerance; Bryden removed all the capacitors without reducing the current, though some measured out of tolerance; Retro Tech Repair's recap changed nothing.[11][5][6] Bryden's schematic numbers four electrolytics, C01 to C04, and eleven other capacitors, but gives no values, so no capacitor list can be given for this game.[2]
Display faults
[edit | edit source]- The game logic does not depend on the display. Bryden's game played its intro music with a dark display until the D882 was replaced.[5]
- A black getter means the tube still holds its vacuum; a white one, as on Retro Tech Repair's spare board with its vacuum port knocked off, means the tube is dead.[6][5]
- 8Bit Retro ReFix says a mark at the top of the screen is made in manufacture and can be ignored.[9]
- A broken tube can only be replaced from another Firefox F-7 or Astro Thunder.[1]
Things that are not faults
[edit | edit source]- The two speakers play different sounds; the box notice says so.[10][4]
- Silence with both speaker switches off.[3]
- The H and L speed indicators clear after a few seconds; speed has to be reselected.[3]
- Flicker seen on video; in person the display is steady.[10]
What is realistically repairable
[edit | edit source]| Part | Status | Source |
|---|---|---|
| D882 (S04), C945 (S03) | Standard parts | [8][5] |
| Ten-way cable | Replace with wire | [5] |
| Cracked board tracks | Wire jumpers | [7] |
| Firing pad | Swap pads, or conductive tape | [7] |
| Transformer (TX-30) | No replacement known; donor only | [11] |
| Microcontroller (D7528C 011) | Donor only | [12] |
| Display tube | Donor only | [6] |
Related pages
[edit | edit source]- Grandstand Firefox F-7
- Grandstand Firefox F-7 General Maintenance
- Grandstand Star Force Troubleshooting Guide
- Grandstand Universal Mains Adaptor
References
[edit | edit source]- ↑ 1.0 1.1 1.2 Handheld Museum, "Grandstand Firefox F-7" (retrieved 2026-10-18): 1983, VFD, four C cells, model 11279; the same game as Epoch Astro Thunder 7, Epoch Galaga X6 and Radio Shack Astro Thunder.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 Philip Bryden, "Grandstand Firefox F7" schematic, three sheets ("Power rail", "Data", "Control Board"), KiCad 6, revision 1, 8 June 2022, PDF on MEGA linked from his video (retrieved 2026-10-18). Drawn by the owner from his own boards and described by him as a first attempt that may need revision. It shows the microcontroller labelled D7528C 011 and a second chip labelled D1771C 011; the display labelled 7AM33T, with its filament on display pins 1 and 2 and 30 and 31; a ten-pin transformer TX-30 driven by transistor S04 (882), whose base is driven by S03 (C945); diodes S05 to S12; electrolytic capacitors C01 to C04 and other capacitors C05 to C15, without values; a 5 MHz resonator X01 (FCR5.0M); and a ten-way cable L01 to the control board, carrying 6 V DC on pin 4. Control board: the power switch; up, down, left and right joystick contacts; select, start and fire; a "sound L" switch for the small piezo speaker and a "sound R" switch for the large one; and a switched DC socket whose centre pin is the negative (ground) side.
- ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 Grandstand, Firefox F-7 instruction booklet (Adam Imports Ltd, Ripon Way, Harrogate; © 1983; made in Japan), hosted here as File:Grandstand Firefox F-7 Instructions.pdf (PDF page numbers). p. 1: drawing of the controls (power switch, left and right speaker switches, joystick, start, skill level select and firing buttons) and the batteries box: four Duracell MN1400 cells; the Grandstand Universal Mains Adaptor, not included, with its polarity switch set to negative; the game will not work properly on weak batteries; if it malfunctions or the display is erratic, check or replace the batteries; switch off after play and remove the batteries when the game is not used for long periods; care note: "move the Joy Stick gently. Do not press hard on the Firing Button ... Do not leave in the sun or allow it to get wet." At switch-on an electronic tune plays and the display lights; skill level 1 shows at the top right; START plays a tune; joystick up selects high speed (H) and down low speed (L) for a few seconds. p. 2: either speaker or both can be switched on, or both off to play in silence. p. 8: a perfect game is 1,000 points.
- ↑ 4.0 4.1 4.2 4.3 Radio Shack, Astro Thunder owner's manual (cat. no. 60-2197; custom manufactured for Radio Shack; printed in Japan), hosted here as File:Radio Shack Astro Thunder Manual.pdf. The same game as the Firefox F-7. p. 1: four C cells in the compartment on the bottom, or Radio Shack's 273-1650 adapter on its 6 V range with the centre tip set negative (270-7001 for 240 V in the UK); check the batteries if the game malfunctions or the display is erratic; take them out if the game will not be used for a week or more, because "even leak-proof type batteries can leak damaging chemicals, which will ruin your unit permanently"; the drawing shows the adapter jack on the right-hand side. p. 2: the LEFT SOUND switch turns the musical sound on and off and the RIGHT SOUND switch the sound effects. p. 7: maintenance: keep it dry, out of heat, dirt and dust; do not drop it; no harsh chemicals, solvents or strong detergents, only a damp cloth; use fresh cells of the correct type.
- ↑ 5.00 5.01 5.02 5.03 5.04 5.05 5.06 5.07 5.08 5.09 5.10 5.11 5.12 5.13 5.14 5.15 5.16 5.17 5.18 5.19 5.20 Philip Bryden, "Grandstand Firefox F-7 | No Power | Faulty Audio | Fiasco", YouTube, 29 May 2022 (transcript read 2026-10-18). A dead Firefox F-7 drawing no current; a centre-negative Mega Drive power lead fits the socket; the case marking calls for negative polarity; six screws (0:10-3:51). The battery terminal wires, marked positive and negative, have to be unsoldered to take the board out (6:41). 6 V reached pin 4 of the ribbon cable and the transformer; the D882 power transistor had died; its base is driven by a small C945 (8:56-11:37). A salvaged substitute fitted the wrong way round drew 0.8 A and burnt his finger (12:50-17:41). Lifting every diode changed nothing (21:02-22:03). Removing the capacitors did not reduce the current, though some measured out of tolerance (23:31-24:01). A new D882 failed again and a second one was fitted; the game then drew about 300-400 mA and the display worked (24:10-28:22). The transformer has ten pins and the board carries an arrow to align it; he found no fault in it (27:29-28:01). The getter was black, "a good sign" (25:31). There is no volume control (25:22). Intermittent sound and a joystick that would not go right were caused by the ten-way ribbon cable inside, which he replaced with wires from an IDE cable (28:35-40:12). The in-game sound effects were still missing at the end; he suspected the sound chip or X01 (40:35-41:03).
- ↑ 6.00 6.01 6.02 6.03 6.04 6.05 6.06 6.07 6.08 6.09 6.10 6.11 Retro Tech Repair, "Fixing a Broken Astro Thunder Handheld - What's Wrong With It?", YouTube, 1 October 2021 (transcript read 2026-10-18; the game is a Grandstand Firefox F-7). The joystick knob can be removed, or lifted and turned, to free the top cover (2:08-2:33). The Fresnel lens is built into the display window (2:41). The battery tabs are soldered and must be unsoldered to free the board (5:04). The getter in the display should be black; on a spare board it had turned white and the tube's vacuum port had been knocked off (6:05-6:44). The D882 tested as "two resistors"; a salvaged one was also bad, and a second worked (7:36-9:14). The keypad must be in place for testing (8:56). The sound was then quiet: cleaning had taken the carbon off the fire pad, so he swapped it with the select pad; the speaker's solder joints and foam pad were renewed (9:31-13:51). The sound chip ran very hot and the current was high; a chip from a spare board behaved the same, and recapping the two supply capacitors changed nothing; the cause was a solder bridge between two tracks on a badly soldered connector, one of them to the sounder (14:24-22:16). The smaller speaker is driven by the main processor and the larger by the second chip, for the more complex sounds (5:28-5:50). Remanufactured moulded battery doors for Astro Wars and Firefox F-7 are "not a perfect fit" but close (22:47-23:02).
- ↑ 7.0 7.1 7.2 7.3 7.4 7.5 StezStix Fix?, "I Paid £30 For an 'UNTESTED' Grandstand FIREFOX F-7", YouTube, 23 April 2022 (transcript read 2026-10-18). A boxed Firefox F-7 with 6 V at the batteries but no power; two case screws missing and a loose broken post rattling inside (0:18-2:47). A crack at a screw post had cracked the board and broken a track; a wire jumper and reflowing some poor joints restored power (2:15-8:21). The board cannot come out without desoldering; he photographed the wiring first (3:20-3:30). The fire button's carbon pad measured about 240 kΩ against 15-45 kΩ for the other pads; copper tape on the pad worked, and he then swapped the fire and select pads (10:05-11:55). The sound is very loud (8:25).
- ↑ 8.0 8.1 8.2 8.3 Retro Tech Repair, "This Vintage VFD Game Has a Hidden Problem", YouTube, 13 August 2019 (transcript read 2026-10-18). A dead Grandstand Firefox F-7 with some battery corrosion, two case screws missing and others replaced with wood screws (1:22-2:56). Peel the sticker off the joystick and undo the Phillips screw to lift the knob off; a vinyl overlay covers the board; the control panel unclips; two sounders, where Astro Wars has one (3:09-4:47). The power switch is in the middle of the board and was bridged with a wire for testing (5:38). The D882 read short between pins 1 and 3; a used D882 from another game cured it (6:26-8:47).
- ↑ 9.0 9.1 9.2 9.3 8Bit Retro ReFix, "Grandstand Fire Fox F7 Repair Part 1", YouTube, 10 April 2021 (transcript read 2026-10-18). Dead, even powered at the battery contacts with the switch bypassed (1:38-6:36). Disassembly: peel the sticker on the end of the joystick and remove the tiny screw so the stick can pass through the case; six base screws, which drop out if the case is tilted back; lift the top straight off (2:26-4:06). A small screw in the middle holds the control board, whose contacts are on the back; one screw at the back and one at the front hold the main board; the DC socket lifts out of its hole in the case (5:39-7:51). The power switch felt greasy (6:36). The D882 had visibly blown, with a burn mark on the board beside it; he believed a wrong-polarity adaptor had done it (11:16-15:10). A mark at the top of the screen was, he said, made in manufacture (10:39-10:43).
- ↑ 10.0 10.1 10.2 10.3 10.4 retro_restos, "Grandstand Firefox F-7 Repair. Vintage Electronic Game Repair 1980's Retro", YouTube, 30 May 2023 (transcript read 2026-10-18). A boxed game with a printed notice explaining that the left and right speakers make different sounds, because owners thought their games faulty (0:58-1:13). Missing battery cover; DC inlet 6 V, negative pin (2:15-2:36). Dead on cells and adaptor: contact cleaner and wiggling the DC socket brought it to life, and contact cleaner and very fine abrasive paper on the battery contacts cleared "a very thin film of oxidation" (3:37-6:23). The ship would not move right; cleaning the joystick contacts and pads with isopropyl alcohol cured it (7:25-19:14). Six screws in the base and a tiny screw in the joystick; an earlier opener had not screwed the screen back properly; a broken stud was plastic-welded (8:58-11:17). Do not polish the printed and painted areas (22:53-23:20). The battery cover is shared by "three or four different models" (25:51). The flicker seen on camera is not visible in person (6:56).
- ↑ 11.0 11.1 11.2 11.3 Repairing Faulty Tech, "Grandstand Firefox F7 REPAIR ATTEMPT! - PART 1", YouTube, 10 August 2024 (transcript read 2026-10-18). A dead Firefox F-7 that had been worked on before: the bench supply went straight into current limiting (0:00-1:57). Diodes and transistors tested good out of circuit; C07 (472K, 4.7 nF) was scorched but measured in tolerance; C10 (473Z, 47 nF) measured 59 nF, also in tolerance (2:27-6:09). A replaced transistor and the removed microcontroller made no difference; the short disappeared when the transformer was removed. He suspected an internal short in the transformer and stopped, expecting no replacement to be available (6:41-12:14).
- ↑ 12.0 12.1 12.2 12.3 Philip Bryden, "Grandstand Firefox F-7 | Astro Thunder | Schematic Download Available", YouTube, 11 June 2022 (description read 2026-10-18; transcript not available): both of his Firefox F-7s had faulty microcontrollers, which he proved by swapping the chips between them; with no replacement chips they could not be repaired; he drew a schematic of the game in KiCad, linked from the description.