Amstrad GX4000 Maintenance Guide

GX4000 main board MC0123C. The RF modulator is at top left, the DC sockets J101 and J102 at top right, and the cartridge connector CE101 in the centre.

The Amstrad GX4000 has one circuit board and an external power adaptor. Maintenance covers the cartridge slot, the power inputs, the connectors and the RF modulator. The console shares its ASIC, processor, memory and sound chip with the Amstrad 464 Plus; the Amstrad 464 Plus Maintenance Guide covers the computer-only parts of that range. Part numbers and adjustments here are from the GX4000 section of Amstrad's service manual and from the user instructions. Faults are in the Amstrad GX4000 Troubleshooting Guide and capacitor values in the Amstrad GX4000 Capacitor Replacement Guide.

Power and safety

The console carries no mains voltage. It runs either from the supplied adaptor, rated 11 V DC 500 mA on the UK model, through the 11 V socket J102, or from 5 V supplied by an MM12 or CM14 monitor through the 5 V socket J101. The adaptor holds the mains transformer; the monitors hold mains voltage and a CRT. See CRT Discharge Procedure before opening a monitor.

Amstrad's instructions for the power leads:

• Connect the DC plug to the console before plugging the adaptor into the mains.
• Use only the supplied adaptor or the power lead from an MM12 or CM14 monitor.
• After use, remove the cartridge and unplug the adaptor from the mains.
• Pull plugs out by the plug, not the wire.

Amstrad listed separate adaptors for the UK (part 270974) and Europe (270973), rated 240 V and 220 V. Check the rating on the label before using an adaptor from another country.

Opening the case

Amstrad's exploded view (p. 31) shows the main board PCB101 lying on a shield plate (111) in the bottom cabinet (112), with the bottom cabinet held by screws marked 203 from underneath. The power-switch bracket (110) and its slide knob (109) are fixed with screws 201 and 202. The top cabinet (105) carries the power/lock knob (103) on a spring (104) and the two cartridge-slot flaps (106 and 107) with their springs (108).

1. Switch the console off, remove the cartridge, and disconnect the adaptor, the monitor leads and the paddles.
2. Turn the console over on a soft cloth and remove the screws from the bottom cabinet.
3. Separate the two halves slowly. The power/lock knob and the flap springs are loose parts in the top cabinet.
4. Note how the slide knob engages the power switch before lifting the board out.
5. On reassembly, check that the flaps spring shut and that the power/lock knob moves freely before refitting the screws.

Cartridge slot

The power/interlock switch turns the console on and locks the cartridge in place. Amstrad's instructions are to switch off before loading or unloading a cartridge, never to force a cartridge, never to touch a cartridge's contacts, and to keep cartridges away from dust and dirt. The cartridge connector, CE101, is on the main board.

• Switch off before touching the cartridge.
• Clean the cartridge edge contacts with isopropyl alcohol on a lint-free swab and let them dry.
• With the case open, inspect CE101 for bent or dirty contacts and for flux or corrosion between pins.
• Check that the cartridge-slot flaps (106 and 107) close under their springs.

The Amstrad 464 Plus Maintenance Guide has the same advice for the Plus computers, which take the same cartridges.

RF modulator adjustment

The only adjustment Amstrad gives for the GX4000 is the frequency of the RF modulator, IC102 (an Astec UM1234E36 on the UK board):

1. Connect the console to a television with the RF lead.
2. Insert a cartridge.
3. Adjust the coil in the RF modulator until the picture shows legible letters.

The user instructions put the signal at about channel 36. The France board drawings have no modulator regulator (IC17), so check which board is fitted before looking for one.

Sound switch

The slide switch on the rear, SW101, selects the sound carrier for the RF output: 6.0 MHz from the ceramic oscillator X101 or 5.5 MHz from X102. Amstrad's user instructions tell the owner to adjust this switch when a television gives no game sound.

Connectors and pinouts

The user instructions (p. 7) give these pinouts.

Monitor socket (8-pin DIN)

Pin	1	2	3	4	5	6	7	8
Signal	Sync (active low)	Green	Luminance	Red	Blue	Left sound	Right sound	Ground

Paddle sockets (9-pin D-type)

Pin	1	2	3	4	5	6	7	8	9
Signal	Up	Down	Left	Right	Spare	Fire 2	Fire 1	Common	COM2 (not on paddle 2)

Auxiliary socket (RJ11)

Pin	1	2	3	4	5	6
Signal	+5 V	Common	Light pen	Fire 2	Fire 1	Ground

• Clean the paddle, DIN and Peritel contacts with a little contact cleaner if a lead gives an intermittent picture or dead controls.
• Amstrad's care notes ask owners not to pull the console about by the paddle leads. Check the paddle cables at the plug and strain relief if a direction or fire button works only when the cable is moved.

Cleaning

Amstrad's instructions are to use only a soft cloth dampened with water on the case, to keep liquids off all the components, and not to expose them to extreme heat or cold. Inside, use a soft brush and low-pressure air on the board.

Capacitors

The electrolytic capacitors are listed, with Amstrad's values and part numbers, in the Amstrad GX4000 Capacitor Replacement Guide. The larger ones sit around the RF modulator, the RGB encoder and the power input.

Tools

• Cross-head screwdrivers and an anti-static strap
• Digital multimeter
• Trimming tool for the modulator coil
• Isopropyl alcohol, foam swabs, contact cleaner and a soft brush
• See Recommended Tools.

Related pages

• Amstrad GX4000 · Amstrad GX4000 Troubleshooting Guide · Amstrad GX4000 Capacitor Replacement Guide
• Amstrad 464 Plus Maintenance Guide – the Plus computers on the same chip set
• Amstrad GX4000 Service Manual · Amstrad GX4000 User Instructions
• CRT Discharge Procedure · Capacitor Failure Symptoms