Atari CX40

Atari CX40 Joystick
Atari CX40 joystick, with the "TOP" marking on the ring beside the fire button
Manufacturer	Atari, Inc.
Type	Digital eight-way joystick
Release date	1978
Interface	9-pin D-sub controller plug, six wires
Compatible	Atari 2600, Atari 7800, Atari 8-bit computers including the Atari XE Game System
Predecessor	CX10 Joystick Controller
Model	CX40 (single), CX40-04 (pair); assemblies CA011693, CA011694, CA011802, CA012994, CA020412

The Atari CX40 Joystick is the eight-way digital joystick that Atari packed with the Atari 2600 (VCS) from 1978 and sold for the Atari 8-bit computers. It has no electronics: five switches on a small printed circuit board connect the four direction lines and the fire line to a common return wire. Atari's 2600 field service manual calls it the Joystick (X-Y) Controller and covers its construction, schematic, test and spare parts.

History

The CX40 replaced the CX10, the joystick shipped with the first VCS consoles in 1977. The two look almost identical. The CX10 has an "ATARI" label on the top of the stick and no "TOP" marking on the ring around its base; inside it has five large spring-loaded buttons. The CX40 has the "TOP" marking at the up position and only one spring, under the fire button. Two CX40s were packed with VCS and 2600 consoles from 1978 to 1984 and with NTSC 2600s in 1984 and 1985; from 1986 to 1991 the 2600 came with one. Units sold for the XE Game System have a grey base to match it.

Atari's patent for the switch mechanism, US 4,349,708 "Joystick control", was filed on 22 August 1979 and names James C. Asher as inventor. It describes a handle pivoting on an axial post, with a resilient ring fixed to the handle that presses on pressure switches arranged around the pivot. The comp.sys.atari.8bit FAQ credits the industrial design to Gerald R. Aamoth and Kevin P. McKinsey. Atari released a new CX40+ in autumn 2023 and a wireless version in autumn 2024.

Construction

Exploded view from US patent 4,349,708: handle (20), circuit board (40) with switches 46 to 50, and the base (12) with the pivot post (32) and four mounting posts (42)

Inside each joystick is a small circuit board carrying five "calculator-type keypads". Four sit in a square under the stick and the fifth under the fire button. Pushing the stick presses the keypad on that side; pushing it diagonally closes two keypads at once, which gives eight directions. Wikipedia's description of the parts matches the patent drawing: the board sits on four posts in the base, a conical post passes through a hole in the middle of the board, and the stick rests on that post with four flexible fingers on the bottom of its moulding, one over each switch. The lid clamps the stick in place and four screws from the underside hold the case together.

Atari's figure 7-1: the earlier board with wires on both edges (left) and the later board with all six wires along one edge (right)

Atari built two versions of the board and its field service manual lists both: CA015396, the two-edged board, and CA016741, the single-edge board. The wires push onto the board on slide-on contacts. Best Electronics says the two boards are interchangeable and gives the wire order on each:

Wire positions on the two CX40 boards (Best Electronics)

Board	Wire order
Two-edged (earlier)	Orange and brown, white and blue, green and black, in pairs across the two edges
Single-edge (later)	Brown, white, black, blue, green, orange, from the top right of the board with the contacts facing you

The FSM notes that the earliest joysticks, with five spring-loaded buttons instead of a circuit board, cannot be repaired. Best Electronics tells the two apart from the underside: on the early CX10-type joystick the four screw heads sit about 3/16 in below the surface of the base, and on the later CX40 about 5/8 in. It reports that the only common part that fits the early type is the cable.

Wiring

CX40 schematic (Atari 2600/2600A FSM figure 7-2)

Switch	Wire colour	Plug pin
Up	White	1
Down	Blue	2
Left	Green	3
Right	Brown	4
Fire	Orange	6
Common (all five switches)	Black	8

Each switch shorts its line to the black common wire, which goes to pin 8, the ground pin of the Atari controller port. The joystick does not use pin 7 (+5 V) or the two potentiometer inputs on pins 5 and 9. On the 2600 the four direction lines are read by the 6532, and the console sees two closures at once as a diagonal.

Testing

Atari's check for the joystick uses a known good VCS, a television and the Combat cartridge:

1. Check the case for damage.
2. Plug in Combat and plug the joystick under test into the left player port.
3. Switch on and press GAME SELECT until game 13 appears, then press GAME RESET.
4. Push the handle away from you: the plane should go down. Pull it towards you: the plane should go up.
5. Move the handle right: the plane should speed up. Move it left: the plane should slow down.
6. Press the red button: the plane should fire.

Best Electronics suggests Missile Command on the 2600 as a test after a rebuild, because it shows all eight directions and the fire button. With the joystick unplugged, a continuity meter between pin 8 and each of pins 1 to 4 and 6 shows each switch closing as the stick or button is pressed, since every switch connects its line to the black common wire.

If a known good joystick also fails, the fault is in the console. Atari's 2600 symptom checklist lists the controller jacks J202 and J203 and motherboard device A202 for "joystick does not work", and points to diagnostic flowchart entry AF.

Common faults

• Worn switches. The top membrane of a switch cracks, or the tape holding the switches in place stops sticking. Best Electronics finds that it is usually the copper contact on the board that wears, not the dome.
• A broken control ring. The ring at the bottom of the stick moulding, or one of the four small tabs joining it to the stick, breaks under too much force. The stick then stops working in that direction.
• A broken pivot. Shake the joystick and listen for loose plastic. If the cone-shaped post in the centre of the base has broken off, Best Electronics considers the joystick not worth rebuilding.
• A fire button that no longer reaches its switch. Heavy thumb pressure can mushroom the small post in the centre of the button, shortening it so that it no longer presses the dome.
• Cable damage. Look for cuts in the outer jacket, exposed copper and sharp bends, particularly where the cable enters the moulded plug, and for damaged or broken contacts inside the plug. One to three empty contact holes in the plug are normal.
• A lost fire button spring. It sits on the centre post of the button, below the board, and falls out easily when the case is opened.

Repair

A CX40 with the base removed, showing the single-edge board, its five metal-dome switches and the six slide-on wire contacts

The FSM limits joystick repair to the parts in its parts list, and Atari also sold a CX41 Joystick Repair Kit, CA020476, containing a circuit board, three springs, an insert, a boot, a retaining ring and repair instructions C020484. Best Electronics' rebuild procedure, for the CX40 with deep screw holes, is:

1. Turn the joystick over and remove the four Phillips screws.
2. Lift the base off slowly, holding the top half with the boot downwards. Note how the board sits on the two locating studs, which way the contacts face (downwards), and which contact is under the fire button.
3. Catch the fire button spring, which sits on the button's centre post below the board.
4. Before taking the old stick out of the boot, note where the square tab on its bottom ring sits. It fits between the two small studs at the 12 o'clock position, with the fire button at 1 o'clock, and the stick fits only one way.
5. Pull the wires off the board by the metal contacts, not by the wires, which come out of the contacts easily. When refitting, put each contact on the right way round: a contact fitted 180 degrees out slides on but does not touch the pad.
6. Twist the six wires into a tight bundle before closing the case, so that a single loose wire cannot be trapped and cut between the two halves.
7. Look down each screw hole with a torch for trapped wires before fitting the screws.

Best Electronics advises replacing the board and the white inner stick together. It reports that boards repaired by fitting new dome contacts under the old tape wore out much sooner than new boards, because the old tape no longer held the domes in place and they moved. Some owners fit miniature snap-action switches instead. Wikipedia notes that switches needing a large force to start moving make diagonals harder, because one of the pair closes before the other.

Service parts

Atari X-Y controller parts (2600 and 2600A parts lists)

Part number	Description
C010726	Cable
C012107-02	Top cover
C012108-02	Bottom case
C012109	Boot
C012110	Retainer ring
C012114	Fire button
C012116	Handle
C012951	Spring
CA015396	PC board (two-edged connection)
CA016741	PC board (single-edge connection)

Best Electronics sells parts under some of these numbers, and gives the original six-conductor joystick cable as CA014058, which differs from the FSM's C010726.

Documentation

• Atari 2600 and 2600A Field Service Manual, section 7 (game controllers) and section 8 (parts lists).

Related pages

• Atari 2600
• Atari 2600 General Maintenance
• Atari 7800
• Atari CX80
• Atari CX85