Jump to content

Grandstand Firefox F-7 Capacitor Replacement Guide

From RetroTechCollection
Grandstand Firefox F-7 Instructions cover
The Firefox F-7 as drawn on the cover of Grandstand's booklet (1983). No freely licensed photograph of its board has been found.

The electrolytic capacitors on the main board of the Grandstand Firefox F-7, Epoch's Astro Thunder 7 under Grandstand's name.[1] No manufacturer's parts list or schematic has been published. An owner, Philip Bryden, drew a schematic from his own boards in 2022; it numbers fifteen capacitors, C01 to C15, draws five of them (C01 to C05) as polarised electrolytics, and gives no values.[2] The values below come from the Korean collector analo9's 2023 recap of an Epoch Astro Thunder 7 on the same main board (96261), whose video shows the five original capacitors set out beside the board and the replacements fitted in their positions; four of the five original values can be read.[3] No repairer of a Grandstand-branded game has published the values. Faults that are not capacitors are on Grandstand Firefox F-7 Troubleshooting Guide; general signs of a failing capacitor are on Capacitor Failure Symptoms.

What the capacitors do on this board

[edit | edit source]

The cells or adaptor supply 6 V through the power switch on the control board and pin 4 of the ten-way cable (L01) to the main board; the negative side is the DC socket's centre pin.[2] On the main board the D882 power transistor S04, driven by the C945 S03, switches current through the ten-pin TX-30 transformer, and diodes rectify its windings into the supplies for the D7528C microcontroller, the second chip (D1771C) and the 7AM33T display, whose filament is fed straight from the transformer.[2][4] Bryden's "Power rail" sheet places the five electrolytics as follows:[2]

  • C01 sits across the 6 V feed from the cable, positive to the 6 V line. It is the reservoir on the supply that feeds the D882 and the transformer.
  • C02, with the 47 nF ceramic C10 beside it, smooths the rail rectified by diodes S09 and S10 from transformer pin 10. The resonator's capacitors C14 and C15 also return to this rail.
  • C03 smooths the rail fed by diode S11 (from transformer pin 4, with C06 across it) and the pair S05 and S06 (from transformer pin 1). This rail runs on through R06 and R04 towards the microcontroller.
  • C04 sits beside diode S12 at pin 4 of the D7528C.
  • C05, with R10, is connected to pin 6 of the D1771C.

Bryden describes his schematic as a first attempt that may need revision.[2]

Capacitor list

[edit | edit source]

Positions are given with the component side facing you and the display standing along the top edge, as in the repair videos. The Grandstand boards in Retro Tech Repair's and Bryden's videos and analo9's Epoch board carry the same board number, 96261, and the same silkscreen: V01 FIP 7AM33T, S01 μPD7528C-011, S02 μPD1771C-011 and I01 TX-30.[5][3]

Firefox F-7 / Astro Thunder 7 main board (96261): electrolytic capacitors
Ref Where it is Role (Bryden's schematic) Original value Voltage Fitted by analo9 Notes
C01 Right-hand edge, below the transformer and the D882, beside diodes S10 and S09 6 V input reservoir 220 µF 16 V Nichicon KMG 220 µF 50 V One of the two largest parts; grey NTK originals on analo9's and Bryden's boards[3][4]
C02 Left of C01, beside diodes S05 and S06 S09/S10 rail, with C10 220 µF 16 V Nichicon KMG 220 µF 50 V The other large one[3][4]
C03 Above C02, at the right-hand end of the D7528C S11 and S05/S06 rail 22 µF 50 V Nichicon KMG 22 µF 50 V Value matched to the part fitted here; a black part on Bryden's board[3][4]
C04 Bottom left, beside diode S12 and resistor R07 Beside S12 at D7528C pin 4 3.3 µF 50 V Nichicon SHL 3.3 µF 50 V Value matched to the part fitted here; lying flat on Bryden's board[3][4]
C05 Top left corner, beside R10, above the D1771C With R10 at D1771C pin 6 Not legible Not legible Nichicon SHL 0.22 µF 50 V The fifth original's marking faces away from the camera[3]

analo9's frame of the removed parts shows two NTK capacitors marked 220 µF 16 V, one marked 22 µF 50 V, one marked 3.3 µF 50 V and a fifth turned away. The two 220 µF parts are the two large ones from C01 and C02. The table assigns 22 µF to C03 and 3.3 µF to C04 because those are the values analo9 fitted at those positions, as he fitted 220 µF (at a higher voltage) at C01 and C02; the video does not show the parts coming out one at a time, so check your own board. Whether C05 was originally 0.22 µF has not been shown.[3]

The silkscreen marks "+" and "−" beside each electrolytic.[6][5] The other ten capacitors are drawn as non-polarised parts. Two of them, both ceramics, have been measured: C07, beside the D882 and marked 472K, is 4.7 nF, and C10, the large disc at the bottom of the board marked 473Z, is 47 nF.[7][6]

Failure signs on the Firefox F-7

[edit | edit source]

No published repair of a Firefox F-7 or Astro Thunder found a capacitor to be the fault:

  • Retro Tech Repair, chasing a sound chip that ran hot and a high current, replaced the two capacitors "across the power supply" without effect; the cause was a solder bridge on a connector. His board afterwards has black replacement parts at C01 and C02.[5]
  • Philip Bryden removed every capacitor from a game drawing too much current. Some measured out of tolerance, but taking them all out did not lower the current; the D882 was the fault.[4]
  • Repairing Faulty Tech found the ceramic C07 scorched and C10 with a hole and a slight bulge; both measured within tolerance.[7]
  • Retro Tech Repair's first Firefox F-7 showed no bulging capacitors; its D882 had failed.[6]
  • analo9 replaced all five electrolytics on his Epoch Astro Thunder 7; the removed parts show no bulging or leakage in his frames.[3]

Because Bryden found some of his capacitors out of tolerance, replace any that measure low or show leakage, but look at the D882 and the ten-way cable first when a game is dead or the sound is missing.[4]

Reading and recording your own board

[edit | edit source]
  1. Photograph the component side square on before removing anything. Note the label number on the board and the date codes on the D7528C and D1771C.[5]
  2. For each of C01 to C05, and C05 above all, write down the value and voltage printed on the sleeve, the maker, the height and whether it stands or lies flat, and which way its stripe faces relative to the "+" on the silkscreen. On most boards the markings face away from the top view, so read them as each part comes out.
  3. Measure each removed part before deciding whether it needs replacing, as Bryden did.[4]

Replacement procedure

[edit | edit source]
  1. Take out the cells. Peel the sticker off the end of the joystick, undo the tiny Phillips screw beneath it and lift the knob off.[8][6]
  2. Remove the six screws in the base (they drop out if the case is tilted back) and lift the top straight off. A vinyl overlay covers the board and the control panel unclips.[8][6]
  3. A small screw in the middle holds the control board, which stays joined to the main board by the ten-way cable. Handle that cable gently: it caused Bryden's sound and joystick faults.[8][4]
  4. One screw at the back and one at the front hold the main board, and the DC socket lifts out of its hole with it. Unsolder the battery wires, marked positive and negative, to free the board.[8][4][5] The full sequence is on Grandstand Firefox F-7 General Maintenance.
  5. Note each capacitor's polarity, then remove it. Keep heat off the display's glass tube, which stands along the top of the board.
  6. Fit new radial electrolytics of the same capacitance and the same or a higher voltage, the right way round, and no taller than the originals so that the top cover still fits. analo9 used 50 V Nichicon parts throughout, including at the two 16 V positions.[3]
  7. Inspect the joints near the cable connectors while the board is out: Retro Tech Repair's high-current fault was a solder bridge there.[5]

After the work

[edit | edit source]
Checks after recapping
Check Expected Source
Supply at ribbon pin 4 About 6 V [4][2]
Current at 6 V About 300-390 mA on one working game [4]
At switch-on A tune plays and the display lights, skill level 1 at the top right [9]
Sound Music from the left speaker, effects from the right, each with its own switch [9][10]

If the current is well above that, switch off and look for a short; a reversed transistor and a solder bridge have each caused it.[4][5] No internal supply voltages have been published for this game.

[edit | edit source]

References

[edit | edit source]
  1. ↑ 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. ↑ 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; "Power rail" sheet read again at full size 2026-10-19). Drawn by the owner from his own boards and described by him as a first attempt that may need revision. Capacitors C01 to C15, no values; C01 to C05 drawn as polarised. C01 between the 6 V line from pin 4 of the ten-way cable L01 and ground (the DC socket's centre pin, labelled GND1); C02 and C10 in parallel between ground and the rail from diodes S09 and S10 (transformer TX-30 pin 10), to which C14 and C15 (the load capacitors of the 5 MHz resonator X01) also return; C03 between ground and the rail from S11 (TX-30 pin 4, with C06 across it) and S05 and S06 (TX-30 pin 1), which continues through R06 and R04; C04 between ground and the junction of R04, diode S12 and pin 4 of the D7528C microcontroller; C05 between pin 6 of the D1771C (with R10) and a line shared with D1771C pins 17 and 22 to 25 and D7528C pin 42. Also: S04 (882) driven by S03 (C945); the display 7AM33T with its filament on TX-30 pins 2 and 6.
  3. ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 analo9 (아날로그 탐구생활), "1983 에포크 아스트로 썬더7 (EPOCH Astro Thunder7, FirefoxF7 repair)", YouTube, 2 November 2023 (description read and frames from 7:36 to 7:54 looked at at full size, 1080p, 2026-10-19). The description (in Korean) calls the Astro Thunder 7 Epoch's 1983 shooting game with sampled sound and says its export version is the Grandstand Firefox F7. The frames show the main board marked 96261 with an Epoch logo, V01 FIP 7AM33T, S01 μPD7528C-011 (NEC D7528C 011), S02 μPD1771C-011 (NEC D1771C 011) and a TDK transformer at I01, silkscreen TX-30; five grey NTK electrolytics removed and laid beside the board, marked 220 μF 16 V, 220 μF 16 V, 22 μF 50 V and 3.3 μF 50 V, the fifth with its marking turned away; the replacements laid out, Nichicon KMG 220 μF 50 V (two), KMG 22 μF 50 V, SHL 3.3 μF 50 V and SHL 0.22 μF 50 V; and the board after the work with the KMG 220 μF parts at C01 and C02, the KMG 22 μF at C03, the SHL 3.3 μF at C04 and the SHL 0.22 μF at C05. The written account of the repair is on analo9's Naver blog, which could not be opened for this page.
  4. ↑ 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 Philip Bryden, "Grandstand Firefox F-7 | No Power | Faulty Audio | Fiasco", YouTube, 29 May 2022 (transcript read 2026-10-18; board frames at 23:30-23:50 looked at, 2026-10-19). 6 V reached pin 4 of the ribbon cable and the transformer; the D882 had died; its base is driven by a small C945 (8:56-11:37). The battery terminal wires, marked positive and negative, have to be unsoldered to take the board out (6:41). "I'm going to remove the capacitors and test them"; "after the capacitors are removed the amperage did not drop, some of the capacitors are out of the limit so they need replacing" (23:31-24:01). A second new D882 cured it; the game then drew about 300-400 mA (24:10-28:22). The ten-way ribbon cable caused intermittent sound and a joystick that would not go right (28:35-40:12). The frames show grey NTK electrolytics at C01, C02 and C04 (C04 lying flat) and small black ones at C03 and C05, with their markings turned away from the camera.
  5. ↑ 5.0 5.1 5.2 5.3 5.4 5.5 5.6 Retro Tech Repair, "Fixing a Broken Astro Thunder Handheld - What's Wrong With It?", YouTube, 1 October 2021 (transcript read 2026-10-18; frames at 18:10-18:58 looked at at full size, 2026-10-19; the game is a Grandstand Firefox F-7). The battery tabs are soldered and must be unsoldered to free the board (5:04). The sound chip ran very hot and the current was high; "I'm starting to suspect these capacitors now, these two go across the power supply ... I'm just going to go ahead and recap this", after which it was "still running hot"; the cause was a solder bridge between two tracks on a badly soldered connector (14:24-22:16). The frame at about 18:42 shows the main board square on: marked 96261-283 with an Epoch logo, V01 FIP 7AM33T, S01 μPD7528C-011, S02 μPD1771C-011, I01 TX-30, S04; electrolytics C01, C02 and C03 at the right, C04 at the bottom left by S12 and C05 at the top left by R10, with "+" and "−" printed beside them; black parts at C01 and C02.
  6. ↑ 6.0 6.1 6.2 6.3 6.4 Retro Tech Repair, "This Vintage VFD Game Has a Hidden Problem", YouTube, 13 August 2019 (transcript read 2026-10-18; frames at 6:40-7:05 looked at at full size, 2026-10-19). 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 (3:09-4:47). "I don't see any bulging capacitors" (6:47); the D882 read short and a used D882 cured it (6:26-8:47). The frame shows the right-hand end of the main board: C01 and C02, the two large electrolytics, beside S10, S09, S05 and S06; C03 above them; ceramics C07, C08, C09 and C10; S04 and its "E C B" markings; "+" and "−" beside each electrolytic.
  7. ↑ 7.0 7.1 Repairing Faulty Tech, "Grandstand Firefox F7 REPAIR ATTEMPT! - PART 1", YouTube, 10 August 2024 (transcript read 2026-10-18). C07, marked 472K (4.7 nF), was scorched but measured "just over 5,000" pF, within tolerance; C10, marked 473Z (47 nF), had a hole and a slight bulge and measured 59 nF, within tolerance (3:53-6:09). The short that put the bench supply into current limiting disappeared when the transformer was removed (10:08).
  8. ↑ 8.0 8.1 8.2 8.3 8Bit Retro ReFix, "Grandstand Fire Fox F7 Repair Part 1", YouTube, 10 April 2021 (transcript read 2026-10-18). 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).
  9. ↑ 9.0 9.1 Grandstand, Firefox F-7 instruction booklet (Adam Imports Ltd, Harrogate; © 1983; made in Japan), hosted here as File:Grandstand Firefox F-7 Instructions.pdf. p. 1: at switch-on an electronic tune plays and the display lights; skill level 1 shows at the top right. p. 2: either speaker or both can be switched on, or both off to play in silence.
  10. ↑ Radio Shack, Astro Thunder owner's manual (cat. no. 60-2197), hosted here as File:Radio Shack Astro Thunder Manual.pdf. p. 2: the LEFT SOUND switch turns the musical sound on and off and the RIGHT SOUND switch the sound effects.


Retrieved from "https://wiki.retrotechcollection.com/index.php?title=Grandstand_Firefox_F-7_Capacitor_Replacement_Guide&oldid=26581"