Grandstand Video Entertainment Computer Troubleshooting Guide

Adman Grandstand Video Entertainment Computer (Schnurrikowski, CC BY-SA 4.0)

Fault-finding on the Grandstand Video Entertainment Computer, the UK version of the Fairchild Channel F System II. No Grandstand service information has been found. The symptom table below combines Fairchild's and Luxor's fault tables for the first-generation console, Luxor's circuit diagram of its System II, and repairs reported by owners, and says which console each finding comes from. Cleaning and voltage checks are covered on Grandstand Video Entertainment Computer General Maintenance, and the electrolytic capacitors on Grandstand Video Entertainment Computer Capacitor Replacement Guide.

Before you start

• Test with the built-in games first. With no cartridge in the slot, switch on and press RESET. "G?" should appear; press 1 for Hockey, then 4, and the game should start with the players responding to the controllers. If the built-in games work, the CPU, the two program storage units, the video circuits and the RAM are at least partly working, and a cartridge fault is more likely to be in the cartridge or the slot.
• Check the television side. The System II sends both picture and sound through the RF output, so set the TV's tuning and volume before suspecting the console. One owner chasing a blank screen found that the fault was in the TV.
• In Fairchild's and Luxor's fault tables, "P S U" is the 3851 program storage unit, the ROM chip holding the built-in program (SL31253 or SL31254), not the power supply. Forum users have read it both ways.
• Keep a circuit diagram to hand. File:Luxor TV Computer Game 1909583 Service Manual.pdf shows the System II processor board and Luxor's mains unit in full, and File:Fairchild Channel F II PAL VHF Schematic 060190-A.jpg is Fairchild's own PAL drawing of the same board. The Grandstand board carries the same main chips.

Symptom table

Symptoms, causes and actions

Symptom	Probable cause	Action
Nothing at all: no picture and no power indication	Mains adaptor, its lead or plug; power-switch board; on Luxor's version, the 80 mA fuse in the mains unit	Measure the adaptor's output with it plugged into the console. Inspect the power-switch board for burnt or leaking capacitors.
Green screen, no "G?" prompt	+12 V missing: the 12 V regulator	Fairchild's table gives "12 volts" as the cause and Luxor's names its 12 V regulator. Measure the 7812's input and output. If +12 V is good, measure -5 V and +12 V on the video RAM pins and +12 V on each 40-pin chip, on the chip pins, and clean oxidised pins.
No picture information at all	+5 V missing	Luxor's first-generation table gives a missing 5 V supply. Measure the 7805's input and output.
Vertical green, black and white lines, no sound, power LED on (System II)	Failed 7805 regulator	On one US System II the 7805 had failed and the CPU was getting too high a voltage; a new regulator cured it. Measure the 7805 output before and after it reaches the chips.
Picture starts with some garbage, then fails or goes blank after seconds to minutes; works again when cold	Heat-sensitive part: on two consoles with the custom-chip board, the FCM 9101/N video chip; also a regulator or capacitor	Two owners traced this by spraying freezer spray on one part at a time while the fault was present: each time the FCM 9101/N video chip restored the picture. Another owner found the 7812 hot when the picture failed. No source for new video chips is known; a replacement has to come from a donor board.
A capacitor on the power-switch board gets hot or bursts at switch-on; TV buzzes or loses signal	Electrolytic fitted backwards by an earlier repair; failed reservoir capacitor	Check every electrolytic's polarity against the board markings and an untouched console. Look for bulged capacitors and clean off any electrolyte. Check the adaptor's output.
Moving bands (hum) in the picture	Rectifier diode or reservoir capacitors; regulators	From Luxor's first-generation table. Check the reservoir capacitors on the power-switch board and the regulators' outputs for ripple; the values are on Grandstand Video Entertainment Computer Capacitor Replacement Guide.
Red or blue dots or "holes" in the picture; stripy, scrambled screen	One of the four video RAM chips	See #Video RAM. RAM failure is common and usually gives a striped, scrambled screen.
Whole screen covered in multicoloured dots or bands; console will not reset	One of the two program storage units (SL31253, SL31254), or a poor contact at its pins	From Fairchild's and Luxor's tables. Clean the chips' pins first. One owner cured graphics corruption by fitting an SL31253 from a donor board.
Garbage on screen, no game sounds, games will not start; or parts of a cartridge game do not work	CPU (SL31291)	Luxor's first-generation table points to the CPU when cartridge functions fail. One owner revived a dead console with a CPU from a donor board, and another proved a System II CPU good by trying it in a first-generation console.
Built-in games work, cartridges do not	Dirty cartridge contacts; flat cables to the cartridge connector; bent springs in the cartridge holder	Clean the Videocart contacts. Check the flat cables are seated. On Luxor's first-generation console the remedy for bent holder springs was a new holder.
Some controller movements do nothing	Broken wire in the controller lead; broken contact spring in the controller; the input buffer	Swap the two controllers between their sockets: if the fault follows the controller, repair the controller (see Grandstand Video Entertainment Computer General Maintenance#Controllers). If it stays with the socket, check the socket and the input buffer: on the System II the controller lines pass through the 9102 audio/buffer chip; on the first-generation console they pass through 74368 and 7404 logic chips.
No colour	Crystal, colour choke or trimmer out of adjustment	From Luxor's first-generation table (4.43 MHz crystal, choke, trimmer capacitor). On the System II the crystal has a 3-15 pF trimmer beside it; adjust it only after checking the TV and the crystal.
Picture drifts or is lost; the TV cannot hold the channel	RF lead or connection	Fairchild's table gives the RF cable as the cause of "out of frequency". Check the lead and its plugs, and the console's channel switch where fitted.

Power rails

The System II's rails, from Luxor's diagram, are +12 V from a 7812, +5 V from a 7805, a +14 V line from a 78L12 and a -5 V supply made on the board for the video RAM. Measured values from US consoles and the measuring points are tabled on Grandstand Video Entertainment Computer General Maintenance#Power supply and voltage checks.

1. Measure the 7812 and 7805 inputs. Low or missing input points to the adaptor, the power-switch board or its capacitors.
2. Measure the outputs. Good input and missing output means a failed regulator.
3. Measure at the chips: +12 V and -5 V on the video RAM (pins 8 and 9, and pin 1), and +12 V and +5 V at the 40-pin chips.
4. If a rail is low only at one chip, look for a cracked joint, a damaged track or, on socketed chips, oxidised pins.

Video RAM

The picture is held in four 4096 × 1-bit DRAMs. On the scanned Grandstand board they are Mostek MK4015N; US System II boards have been reported with SCM90004C chips and Luxor's diagram labels them "330470".

Finding the bad chip

The two bits of each pixel are stored in different chips, so a faulty chip shows as dots, holes or stripes in one colour. Fairchild's test cartridge for the first-generation console showed red and blue sweep bars and tied holes in the blue bar to RAM D9 or D10 and holes in the red bar to D7 or D8; Luxor's first-generation table gives E9 or E10 for red dots and E7 or E8 for blue. The board positions differ on the System II, where Luxor's diagram labels the four chips EVEN 0, ODD 0, EVEN 1 and ODD 1. Where the chips are socketed, swapping them round shows whether the fault moves with a chip.

Choosing a replacement

The two generations of board feed their RAM differently, and a substitute that suits one may not suit the other.

• VESwiki gives MK4027-compatible DRAM for the first-generation board and MK4015N-compatible DRAM for the second generation, which includes the System II.
• Luxor's diagram of the System II board shows -5 V on pin 1 and +12 V on both pins 8 and 9 of each RAM chip.
• On a second-generation board, an MK4027N-3 gave a black screen and became very hot within seconds. A RAM chip taken from a first-generation console worked in the same position.
• On a first-generation console, one owner had to replace all four chips with MK4027 at once: a mixture of old and new chips gave glitches and resets.
• VESwiki describes fitting 4164 DRAMs, which run from +5 V alone, with pin 8 lifted and joined to pin 9 and a 1 nF capacitor from pin 14 to ground, in what it calls the "System Fairchild unit"; it does not say which generation of board that was. The change relies on pin 9 carrying +5 V, as on the MK4027 pinout. On the System II, Luxor's diagram puts +12 V on both pins 8 and 9, so a 4164 fitted that way would receive +12 V. Do not fit 4164s to a System II without working out the supplies first.

Custom and programmed chips

Chips that can only be replaced from a donor board

Chip	Function	Notes
SL31291 (3850)	CPU	A System II's CPU has been tested in a first-generation console, so the two take the same part
SL31253 and SL31254 (3851)	Program storage units with the built-in program	Mask-programmed ROM; cannot be reprogrammed with an EPROM programmer
FCM 9102	Controller input buffer and tone output	Not on the first-generation (standard logic) board
FCM 9101/N or FCM 9111 (Luxor diagram: 9111; Fairchild PAL drawing: 9101)	Video	Not on the first-generation (standard logic) board. Reported heat-sensitive on two consoles; VESwiki's author warns that a failed one is very hard to replace

Clean and reseat the pins of a suspect chip, and check its supplies, before condemning it. VESwiki's author cautions that a chip which seems faulty may only have oxidised pins or a poor socket contact.

First-generation fault tables

Fairchild's and Luxor's own fault tables were written for the first-generation console, which builds the video circuits from standard logic chips. The supply, RAM, program storage unit, CPU, cartridge holder and controller entries carry over to the System II; the entries for individual logic chips do not, because the System II replaces those chips with its two custom chips.

Luxor service bulletin No. 5, 15 February 1979, for the first-generation console type 190 9574 (translated from Swedish)

Symptom	Cause given	Applies to System II?
Green screen, no game (G?) prompt	Q6, 12 V regulator faulty	Yes: the 12 V supply
No information on the screen	Q5, 5 V missing	Yes: the 5 V supply
Colour fault (no colour)	The 4.43 MHz crystal or choke L4; check trimmer capacitor C25 and adjust if needed	In principle; part numbers differ
Moving bands (hum)	Faulty rectifier diode or electrolytic C4, C5, and Q5 and Q6	Yes: rectifier, reservoir capacitors and regulators
Dots visible on the screen (blue or red)	ICs E9, E10 for red; E7, E8 for blue	Yes: video RAM, at different positions
Whole screen covered in multicoloured dots or bands	C10 (SL31254), C8 (SL31253)	Yes: program storage units
No sync, picture looks overdriven	D1 (7486)	No: logic chip not on the System II
Intermittent sync fault (heat fault)	F8 (7493)	No: logic chip not on the System II
Some functions of a cartridge do not work	Check C7 (SL31291)	Yes: CPU
No information from the cartridge	Springs in the cartridge holder bent upwards; replace the whole holder	Possibly: holder design not documented for the System II
Horizontal bands (green, blue, red, usually only two)	E6 (7400)	No: logic chip not on the System II
Some typical functions of a hand controller do not work	Break in the cable or a broken contact spring; also check A10 (CTS 7715), A9 and A8 (74368), A7 (7404)	Cable and contacts yes; on the System II the buffering is in the 9102

Translated from File:Luxor TV Computer Game 1909574 Service Manual.pdf; System II comparison from Luxor's System II diagram.

Fairchild's own "Analysis Aid" for the original console gives four conditions, "no reset" (PSU), "green screen" (12 volts), "weak sound" (speaker binding) and "out of frequency" (RF cable), followed by eighteen numbered photographs of faulty screens with their causes, which range from the PSU, the RAM and the CPU to colour and frequency adjustment; several are marked as needing detailed analysis. Wikipedia says the System II has no internal speaker, but Luxor's System II has a loudspeaker in its parts list and circuit diagram, so the speaker entry may apply to some versions.

Related pages

• Grandstand Video Entertainment Computer
• Grandstand Video Entertainment Computer General Maintenance
• Grandstand Video Entertainment Computer Capacitor Replacement Guide
• Capacitor Failure Symptoms
• Category:Grandstand