Atari 2600

Atari 2600

Atari 2600 4-switch "woodgrain" model
Specifications
Manufacturer	Atari, Inc.
Type	Home video game console
Released	September 1977 (as Video Computer System)
Intro price	US$199 (1977)
CPU	MOS Technology 6507 (Atari C010745)
Memory	128 bytes RAM (within the 6532 RIOT)
Storage	ROM cartridge
Display	160 × 192 visible pixels (NTSC)
Sound	TIA, 2 channels, mono
OS / Firmware	None
Predecessor	Dedicated Pong consoles
Successor	Atari 5200
Codename	Stella
Model no.	CX2600, CX2600A, 2600 Jr.

The Atari 2600, originally sold as the Atari Video Computer System (Atari VCS), is an 8-bit home video game console developed and manufactured by Atari, Inc. Released in September 1977, it popularised the ROM cartridge and established the home console market. It is built around the MOS Technology 6507 processor and the custom Television Interface Adaptor (TIA), which generates the video signal in real time without a frame buffer.

This page concentrates on the information a repairer needs. Component values and service modifications are on the Atari 2600 Capacitor Replacement Guide.

How the machine is built

Atari's field service manual divides the console into two assemblies, and knowing which is which saves a great deal of time when diagnosing:

• Switchboard (6-switch machines). Carries the player-option switches, the entire power supply — regulator, filter capacitors and the on/off switch — and the RF modulator. Unregulated DC arrives here from the external supply, which Atari calls the "battery eliminator". +5 V is routed through a filter to the RF modulator and to the motherboard.
• Motherboard. Carries the 6507 MPU, the 6532 RAM-I/O-timer and the TIA, inside RF shielding.

The two are joined by a 12-conductor flexible ribbon cable, which also carries video and sound from the TIA to the RF module. If a 6-switch machine is dead, the fault is more likely to be on the switchboard than the motherboard, because that is where the power supply lives.

The 4-switch CX2600A and the 2600 Jr. consolidate everything onto one board.

Model variants

Production models

Model	Board	Description
Heavy Sixer	CX2600	Six front switches, two-board design, thick base moulding
Light Sixer	CX2600	Cost-reduced six-switch, same two-board architecture
4-Switch Woodgrain	CX2600A	Difficulty switches moved to the rear, single board
4-Switch Vader	CX2600A	All-black case, same board family
2600 Jr.	—	Smaller cost-reduced single board. Not covered by Atari's field service manual

Atari's service documentation groups the CX2600A boards into three bands, and issues a separate schematic and silkscreen for each: Revs 1–13, Revs 14 and 15, and Revs 16 and up. The revision number is printed on the board and determines which service modifications apply:

• Revs 1–13 need the static-protection strips on the front-panel switches.
• Revs 1–13 are the boards covered by the February 1982 C241/C242 bulletin.
• Revs below 16 may lack the 820 Ω blanking resistor between TIA pins 6 and 9, which Atari incorporated into the design from Rev 16.
• Rev 16 and up omit C201.

All three are described in detail on the Atari 2600 Capacitor Replacement Guide.

Integrated circuits

Atari part numbers and board locations

Location	Atari P/N	Device	Function	Package
A200	C010745	MOS 6507	Microprocessor	28-pin DIP, socketed
A201	C010444	TIA	Television Interface Adaptor: video, sound and the paddle A/D	40-pin DIP, socketed
A202	C010750	MOS 6532	RAM-I/O-timer (RIOT/PIA): 128 bytes RAM, two 8-bit ports, timer	40-pin DIP, socketed
A203 (CX2600, Revs 1–13)	C010816	4050B	Hex buffer for video and the joystick trigger lines
A203 (CX2600A, Rev 14+)	C014348	78M05	+5 V regulator, TO-220
A205 (CX2600A, Rev 14+)	—	555	Timer
A101 (CX2600 switchboard)	C014348	78M05	+5 V regulator, TO-220

The CPU, TIA and RIOT are socketed on both boards, so a donor chip can be swapped in without desoldering. Atari's service checklist notes that boards fitted with Molex sockets with insertion aids should have the aids removed and the chip reseated — a known cause of intermittent contact.

The hex buffer is the component most often killed by static discharge through the controller ports, which is why Atari issued a retrofit for it in February 1982.

Power supply

The console is supplied from an external unregulated DC adapter. Regulation to +5 V is done inside the console by a 78M05 — a 500 mA regulator, not the 1 A 7805 — at A101 on the 6-switch switchboard or A203 on a 4-switch board. Atari's own documents are not quite consistent here: the parts lists specify the 78M05 (P/N C014348) and the IC pinout page names the National LM340 and Texas Instruments 78M05C, while the CX-2600A schematic simply prints "7805" in the regulator symbol. Fitting a 7805 is a sensible upgrade, but the part Atari ordered was the 500 mA device.

The input connector is a 3.5 mm mono phone jack (J201 in Atari's CX2600A parts list), not a barrel connector. On the CX2600A schematic the tip contact carries the positive supply and the sleeve is grounded.

Expected readings, from Atari's own diagnostic flow charts:

Test point	Expected
Regulator input (A101 pin 1)	7.5–9 V unregulated DC
Regulator output (A101 pin 3)	+5 V
J101 pin 1 (switchboard to motherboard)	+5 V
J101 pin 2	approximately +9 V
RF module supply (pin 3 of a 5-pin module, pin 2 of a 3-pin module)	+5 V
RF module output	tuned to 61.23 MHz

If +9 V is present at J101 pin 2 but +5 V is missing, Atari's flow chart directs you to check C101, C103 and C106 for shorts before condemning the regulator.

Video and audio timing

Figures from Atari's Stella Programmer's Guide:

• An NTSC frame is 262 scan lines: 3 lines of VSYNC, 37 of VBLANK, 192 of picture and 30 of overscan.
• Each line is 228 colour clocks at 3.58 MHz — 160 visible pixels plus 68 clocks of horizontal blanking.
• The 6507's clock is the 3.58 MHz colour clock divided by three, which gives the programmer 76 machine cycles per scan line. This is the origin of the "racing the beam" programming style.

The colour-clock crystal is X200 on the motherboard; Atari's parts list prints it as 3.579575 MHz.

The TIA's two sound channels are mixed to mono and modulated onto the RF carrier. The sound subcarrier is generated by a tuned circuit built from L201 and the two 820 pF polystyrene capacitors C206/C207, which is why those two capacitors silence a console when they drift.

Memory map

6507 address space

Range	Contents
$0000–$007F	TIA registers
$0080–$00FF	6532 RAM, 128 bytes. The stack grows down from $FF, variables up from $80
$0282	SWCHB — console switches (read only)
$0284	INTIM — read the timer
$0294–$0297	TIM1T, TIM8T, TIM64T, TIM1024T — set the timer interval
$1000–$1FFF	Cartridge ROM

The 6507 brings out only 13 address lines, so the visible address space is 8 KB and every region above is mirrored repeatedly.

Controller ports

The two DE-9 ports carry four direction switches and a trigger, plus two analogue lines used by the paddle controllers. The trigger lines run to the 4050B hex buffer, and the paddle lines run to the TIA, which contains the analogue-to-digital conversion circuitry.

Paddle controllers use a 1 MΩ variable resistor (Atari's paddle parts list). The paddle timing capacitors on the console side are the 0.068 µF epoxy-dipped parts at C215–C218 (CX2600) or C218–C221 (CX2600A).

Because the trigger lines connect directly to a CMOS buffer, static discharge through the ports is the classic way to kill a 2600. Atari's February 1982 retrofit fits a 1N4736 6.2 V zener in parallel with the existing 220 pF capacitor on each trigger line, in the C236/C237 positions, with the banded end facing the connectors, together with static strips on the switches. Details are in the Atari 2600 Capacitor Replacement Guide.

Diagnostics

Atari's service network used a Diagnostic Test Cartridge (version 2.6) containing a RAM test, colour bar test, grey bar test, diagnostic matrix test, audio tones test and paddle control lines test, backed by a Signal Trace Cartridge for tracking motherboard faults the diagnostic cartridge cannot reach. Both cartridges and the full flow charts are reproduced in the field service manual, which remains the most efficient way to diagnose a 2600 systematically.

Common service points

From Atari's own inspection checklist, applied to every 2600 that came in for service:

• Fit the static-protection modification to any 2600 that does not have it.
• Check every connector and plug for a tight fit; intermittent faults very often come from a loose connector.
• Check J202/J203 for pushed-back or broken pins.
• If the cartridge connector J200 is the green type and the machine is intermittent with a cartridge inserted, replace the connector.
• Check the components around the perimeter of the motherboard for dry joints and check for broken or shorted traces.
• On a machine with a standup regulator and heatsink, look for hairline fractures between the regulator and the switchboard and make sure the regulator is properly clipped or riveted to the heatsink.
• Boards at Rev 8 or lower should have a coloured dot over the trace at the upper-left corner, which prevents the board shorting against the casting.
• Where a flat-wire 12-conductor cable assembly is faulty, replace it with the ribbon cable assembly (C012776) and fit the 12-pin female switchboard socket (C014778-03).

Cartridge slot

The cartridge connector is a 24-pin (2 × 12) edge connector. Standard cartridges are 2 KB or 4 KB, directly mapped at $1000–$1FFF; larger cartridges use bank-switching schemes implemented in the cartridge rather than in the console, and some add RAM or a coprocessor on the cartridge board.

Maintenance and repair

• Main article: Atari 2600 General Maintenance
• Main article: Atari 2600 Troubleshooting Guide
• Main article: Atari 2600 Capacitor Replacement Guide

Schematics

Atari 2600 PAL

Motherboard	Control Panel	RF Modulator
Atari 2600 Console Schematic - PAL	Atari 2600 Control Panel Schematic - PAL	Atari 2600 Modulator Schematic - PAL

Atari 2600 - CX2600 - NTSC

Motherboard - CX2600	Motherboard - CX2600 A	RF Sections
Atari 2600 CX2600 Schematic - NTSC	Atari 2600 A Schematic - NTSC	Atari 2600 RF Sections Schematic - NTSC

Atari 2600 Accessories

Accessories	CX22 Trackball
Atari 2600 Accessories Schematic	Atari 2600 CX22 Schematic

Service documentation

• Atari 2600/2600A Domestic VCS Field Service Manual (PDF) — parts lists, schematics, flow charts and service bulletins
• Atari 2600 and 5200 Field Change Orders, Upgrade Bulletins and Tech Tips (PDF)
• Stella Programmer's Guide (PDF)

Related pages

• Atari 2600 General Maintenance
• Atari 2600 Troubleshooting Guide
• Atari 2600 Capacitor Replacement Guide
• Atari 5200