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Grandstand Video Entertainment Computer General Maintenance

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Grandstand-video-entertainment-computer-pcb
Grandstand Video Entertainment Computer main board: RF section top left, electrolytic capacitors at the top right of centre, CPU and PSUs on the right, video RAM bottom left (Incog88, CC BY-SA 3.0).

Cleaning, power checks and care for the Grandstand Video Entertainment Computer, the UK version of the Fairchild Channel F System II. The newest of these consoles are now over 45 years old. No Grandstand service manual has been found. The sources are Luxor's service manual for its own version of the System II, Fairchild's PAL circuit diagram of the System II board, Fairchild's notes for the original Channel F, the VESwiki Channel F reference and owners' repair reports.[1][2][3][4] Most of it applies to any Channel F System II. Fault-finding by symptom is on Grandstand Video Entertainment Computer Troubleshooting Guide.

Safety

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  • The console itself runs on low voltages, the highest being the unregulated rail of about 20-24 V that feeds the 12 V regulator.[1][5]
  • The mains adaptor contains a transformer whose primary is at mains voltage. Unplug it before opening it, and check its case and lead for cracks or damage before each use. Luxor's version of the console has its transformer and an 80 mA slow-blow fuse inside the case instead.[1]
  • The large electrolytic capacitors on the power-switch board (1000 µF and 2200 µF on US consoles) must go in the right way round. On one US System II a previous repairer had fitted both backwards, and the replacement capacitors overheated and burst within seconds of switching on.[5]

Opening the console

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No disassembly procedure for the Grandstand or the System II has been published. Owners of US System II consoles report:

  • The board sits under a metal RF shield, and the 7812 and 7805 regulators are mounted with their tabs against the metal case, which acts as their heatsink.[5]
  • On one console, which had been partly taken apart before, the cartridge eject button pulled off "like a lego brick" and the RF shield was held only by spring pressure. Another owner left the shield in place because it wraps around the eject button and he did not want to break it.[5]
  • The power switch and its two large capacitors are on a separate daughter board.[5]

Before taking anything apart, photograph the board, the wiring to the power-switch board and the orientation of each regulator and electrolytic capacitor. Replacement eject buttons and front-panel buttons for the System II have been published as 3D-printable files if one breaks.[6]

Cleaning

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Case and buttons

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Clean the case with a damp cloth and mild detergent, keeping water away from the buttons, the cartridge slot and the connectors. The five front-panel buttons respond to a short press; Fairchild's leaflet says not to hold them down for more than a second.[7] 3D-printable replacement buttons are available for both the original console and the System II, which has smooth-topped buttons.[6]

Cartridge slot and Videocarts

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Switch off before inserting or removing a Videocart. The cartridge connector carries +5 V on contacts 19 and 20 and +12 V on contact 22 to the program storage units inside the cartridge.[8]

  • Clean the Videocart's edge contacts with isopropyl alcohol on a cotton bud and let them dry before use.
  • Inside the console, the cartridge connector reaches the main board through flat cables (an 8-way and an 11-way cable in Luxor's parts list). Check that they are fully seated if the built-in games work but cartridges do not.[1][9]
  • On the first-generation Luxor console, bent-up springs in the cartridge holder stopped it reading cartridges, and Luxor's remedy was to replace the whole holder.[10]

Chip pins

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The Channel F's 40-pin chips (the CPU, the two program storage units and, on the System II, the two custom chips) often have pins oxidised black, which VESwiki's author attributes to their silver content. Where the chips are in sockets, polishing the pins can restore a poor connection.[11] The board scan does not show whether the Grandstand's chips are socketed.[12]

Power supply and voltage checks

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Luxor's circuit diagram is the reference for the System II's supplies. A transformer, rectifier and two reservoir capacitors give two unregulated rails; on the processor board, regulators derive +12 V, +5 V and a +14 V line from them, and a small transistor circuit makes -5 V for the video RAM.[1] Owners of US consoles have measured the same arrangement.[5]

System II supply rails
Rail Made by (Luxor 9583) Where to measure Expected
Upper unregulated rail Rectifier and 1000 µF reservoir Input of the 7812 +20 V on Luxor's diagram; 23-24 V measured on US consoles
Lower unregulated rail Rectifier and 2200 µF reservoir Input of the 7805 +10 V on Luxor's diagram; about 11.6-12 V measured on US consoles
+12 V µA7812 (Q5), 100 µF output capacitor (two 100 µF on the Grandstand board) 7812 output; video RAM pins 8 and 9; cartridge contact 22 +12 V
+5 V µA7805 (Q4), 47 µF output capacitor (two 47 µF on the Grandstand board) 7805 output; cartridge contacts 19 and 20 +5 V
+14 V µA78L12 (Q6) with a 1200 ohm resistor 78L12 output +14 V
-5 V Transistor Q1 and diodes, about 800 µA Video RAM pin 1 -5 V

Rails, regulators and RAM pins from Luxor's diagram;[1] measured inputs and outputs from US System II owners;[5] cartridge contacts from VESwiki.[8]

  1. With the console unplugged, check the reservoir capacitors on the power-switch board for bulging and leaks, and the board for electrolyte residue.[5]
  2. Switch on and measure the input and output of each regulator. A regulator with good input and no output has failed; on one System II a failed 7805 left the console showing only vertical lines, with no sound.[9]
  3. If the regulators are right, measure +12 V and -5 V on the video RAM pins and +12 V on each 40-pin chip, on the chip pins themselves, as VESwiki's author recommends.[11]
  4. A regulator that runs very hot is either faulty or supplying too much current. One owner replaced both regulators without curing a picture that failed after a few minutes, then found the 7812 hot to the touch when it failed; the thread ends without a cure.[5]

Capacitors

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The main board has four axial electrolytic capacitors, two 25 V 100 µF on the +12 V rail and two 25 V 47 µF on the +5 V rail; the large reservoir capacitors are in the power section.[12][1][2] Values, positions, the power-section capacitors of the Luxor and US versions, the replacement procedure and the voltages to check afterwards are on Grandstand Video Entertainment Computer Capacitor Replacement Guide. See Capacitor Failure Symptoms for what a failed capacitor looks like.

Controllers

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  • Hold the controller with the recessed triangle on the knob towards the screen, and do not twist or wrench the knob violently.[7]
  • Do not wind the lead tightly round the controller for storage. Repairers of the first-generation console's wired controllers find that the wires are thin, with few strands, and break where the lead bends out of the bottom of the controller.[13]
  • To repair a broken lead, cut it back past the break, retest, and resolder the wires inside the controller; take photographs of the wire routing first. VESwiki's author fixes the lead inside with a small cable tie after drilling the old cable out of the strain relief. A joystick extension lead can be used as new cable, but its colours will not match, so check each wire with a meter.[13]
  • To test a lead and its contacts, unplug the controller and check each pin of its 9-pin plug against pin 9 (ground) with a continuity meter while working the matching movement. The pin assignment is on Grandstand Video Entertainment Computer#Controllers and front panel.[8]
  • Fairchild's service notes for the original console describe the inside of its hand controller: contact pins for each movement, a ground ring, and a factory modification that added plastic tubing to the contacts. No equivalent notes have been found for the System II controller.[3]
  • VESwiki publishes "Test Controls", a homebrew program that shows every button and controller movement on screen. It needs a way to run homebrew software on the console, such as a multicart.[14]

Video RAM

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The four video RAM chips are the parts owners most often replace. Before buying substitutes, read Grandstand Video Entertainment Computer Troubleshooting Guide#Video RAM: the System II board feeds its RAM differently from the first-generation board, and a substitute that suits one can overheat in the other.[15][1]

Preventive maintenance checklist

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  1. Inspect the mains adaptor's case, lead and plug.
  2. Clean the Videocart contacts and the case.
  3. Store the controllers without winding their leads tightly.
  4. Switch on with no cartridge, press RESET, then 1 and 4: Hockey should start.[7]
  5. Run a known-good Videocart.
  6. If the console has been opened, check the regulator input and output voltages and look over the power-switch board's capacitors.
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References

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  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 Luxor, Service Manual, TV Computer Game, type 190 9583, May 1980. Hosted here as File:Luxor TV Computer Game 1909583 Service Manual.pdf: mains unit (80 mA T fuse, transformer, 1N4001 rectifiers, CN02 1000 µF on +20 V, CN03 2200 µF on +10 V, CN01 47 µF); processor board: Q4 µA7805 with C50 47 µF, Q5 µA7812 with C52 100 µF, Q6 µA78L12 with R2 1200 ohms for +14 V, Q1 -5 V at 800 µA; video RAM pin 1 on -5 V and pins 8 and 9 on +12 V; flat cables 8-way and 11-way in the parts list.
  2. ↑ 2.0 2.1 Fairchild Camera and Instrument, Video Products Division, drawing 060190-A, "IC PAL VHF Schematic". Hosted here as File:Fairchild Channel F II PAL VHF Schematic 060190-A.jpg (from VESwiki, where it is published as the SABA Videoplay 2 schematic): U1 3850 CPU; U2 and U3 3851 PSUs; U4 9101 video; U5 9102 audio/buffer; U6-U9 "330470" RAM; Y1 8.867238 MHz with C18 3-15 pF trimmer; Q4 7805 with C50 47 µF on +5 V; Q5 7812 with C52 100 µF on +12 V; -5 V at 800 µA.
  3. ↑ 3.0 3.1 Fairchild, Service Manual for the Video Entertainment System, c. 1976. Hosted here as File:Fairchild Video Entertainment System Service Manual.pdf: section I, hand control modification (contact positions, plastic tubing, ground ring), first-generation console.
  4. ↑ VESwiki (channelf.se), "VRAM" (retrieved 2026-10-18): video RAM types for the first and second generations of console.
  5. ↑ 5.0 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 AtariAge Forums, "Explosive Fairchild Channel F problems", August 2018 to June 2020 (retrieved 2026-10-18): US System II with external power brick; power-switch daughter board whose 25 V 1000 µF and 2200 µF capacitors had been fitted backwards by a previous repairer, replacements overheating and bursting; electrolyte residue on the daughter board; a capacitor with one leg unsoldered; µA7812 and µA7805 tabs against the metal case; 23.3 V to 12.19 V and 11.63 V to 5.03 V measured, and 24 V in, 12 V in reported on another console; 7812 hot when the picture failed; eject button pulling off and RF shield held by spring pressure on one console.
  6. ↑ 6.0 6.1 Nathan Mitchell (Parzval47), 3D-printable "Fairchild Channel F Replacement Buttons" (Thingiverse 4741287; for the original console and the System II, which has smooth-topped buttons) and System 2 cartridge eject buttons (4747828, 4745385), 2021, CC BY 4.0, mirrored on the Internet Archive as thingiverse-4741287, thingiverse-4747828 and thingiverse-4745385.
  7. ↑ 7.0 7.1 7.2 Fairchild Video Products, Channel F System II: Playing Tennis / Playing Hockey. Hosted here as File:Fairchild Channel F System II Built-in Games Instructions.pdf: starting Hockey with RESET, 1 and 4; selector buttons not to be held down for more than a second; knob triangle towards the screen; do not violently twist or wrench the controllers.
  8. ↑ 8.0 8.1 8.2 VESwiki, "Pinouts" (retrieved 2026-10-18): cartridge connector (ground 1 and 2, +5 V 19 and 20, +12 V 22) and the 9-pin hand controller plug of the Channel F II, Grandstand, Nordmende and Luxor consoles (pin 9 ground).
  9. ↑ 9.0 9.1 AtariAge Forums, "Fairchild Channel F System 2 Chip", February 2020 (retrieved 2026-10-18): System II with vertical green, black and white lines and no sound, cured by replacing a 7805 whose output had failed; the ribbon cable to the cartridge reader.
  10. ↑ Luxor, Service Manual, TV Computer Game, type 1909574, August 1978, with service bulletin No. 5, 15 February 1979. Hosted here as File:Luxor TV Computer Game 1909574 Service Manual.pdf: first-generation console; "no information from cassette" caused by bent springs in the cartridge holder, remedy to replace the holder.
  11. ↑ 11.0 11.1 AtariAge Forums, "Fairchild Channel F Green Screen", October 2020 (retrieved 2026-10-18): advice from e5frog (Fredric Blåholtz, author of VESwiki): green screen means check 12 V; then check -5 V on the RAM and 12 V on each 40-pin chip, on the chip pins; the 40-pin chips' pins are often oxidised black and polishing them can cure a poor socket contact.
  12. ↑ 12.0 12.1 Incog88, scan of the Grandstand Video Entertainment Computer main board, from Wikimedia Commons (CC BY-SA 3.0), read at full size: four axial electrolytics, two 25 V 100 µF above two 25 V 47 µF, at the top of the board right of centre, above the CPU; chip markings; no designators legible.
  13. ↑ 13.0 13.1 AtariAge Forums, "Fairchild Channel F Repair - Help Request", October 2016 to May 2017 (retrieved 2026-10-18): controller lead wires thin and breaking where the lead bends out of the controller, especially when wound round it; repair by cutting back and resoldering, drilling out the strain relief and securing with a cable tie (e5frog); joystick extension lead as replacement cable with a different colour order.
  14. ↑ VESwiki, "Homebrew:Test Controls" (retrieved 2026-10-18): input test program by Fredric Blåholtz, 2007, with binary and source.
  15. ↑ AtariAge Forums, "Fairchild Channel F Model 2 - RAM type?", December 2019 to November 2021 (retrieved 2026-10-18): an MK4027N-3 fitted to a second-generation (VLSI) board gave a black screen and became very hot; a RAM chip from a first-generation console worked.


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