Editing Atari 2600 Troubleshooting Guide (section)

== Component reference and test points (deep dive) ==

The 2600 is essentially three chips plus glue logic:

<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table" style="width:100%; text-align:left;"
! Chip !! Role !! Notes
|-
| 6507 || CPU || 28-pin cut-down 6502 (no IRQ/NMI, 13 address lines = 8 KB), clocked at '''1.19 MHz'''
|-
| TIA || Television Interface Adapter || Video, audio and controller reads; divides the '''3.58 MHz''' colour crystal by three to clock the CPU
|-
| 6532 (RIOT) || RAM-I/O-Timer || 128 bytes of RAM, the console-switch/joystick I/O ports, and the timer
|}
<ref name="a2600">[https://retro64.altervista.org/blog/atari-2600-and-7800-repair-tales/ Atari 2600/7800 repair tales], Retro64; [http://blog.tynemouthsoftware.co.uk/2015/02/atari-2600-black-screen-repair.html Atari 2600 Black Screen Repair], Tynemouth Software; and [https://consolemods.org/wiki/Atari_2600:General_Troubleshooting ConsoleMods Wiki]. Source for the three-chip architecture (6507 CPU at 1.19 MHz, TIA, 6532 RIOT), the dirty-cartridge-contact cause of blank/corrupt screens, the 3.58 MHz crystal / TIA clock division, the RIOT socket contact fault, and the cold-solder reflow.</ref>

=== Blank / no picture ===

* '''Clean the cartridge contacts first''' — dirty cart contacts are the number-one cause of wrong colours, missing sprites and corruption. A blank screen is usually the '''TIA''', but any of the three main chips can cause it.<ref name="a2600">[https://retro64.altervista.org/blog/atari-2600-and-7800-repair-tales/ Atari 2600/7800 repair tales], Retro64; [http://blog.tynemouthsoftware.co.uk/2015/02/atari-2600-black-screen-repair.html Atari 2600 Black Screen Repair], Tynemouth Software; and [https://consolemods.org/wiki/Atari_2600:General_Troubleshooting ConsoleMods Wiki]. Source for the three-chip architecture (6507 CPU at 1.19 MHz, TIA, 6532 RIOT), the dirty-cartridge-contact cause of blank/corrupt screens, the 3.58 MHz crystal / TIA clock division, the RIOT socket contact fault, and the cold-solder reflow.</ref>
* Confirm the '''3.58 MHz''' colour crystal is oscillating and that the TIA is producing the divided '''1.19 MHz''' CPU clock, and that RESET releases (goes high) shortly after power-on.<ref name="a2600">[https://retro64.altervista.org/blog/atari-2600-and-7800-repair-tales/ Atari 2600/7800 repair tales], Retro64; [http://blog.tynemouthsoftware.co.uk/2015/02/atari-2600-black-screen-repair.html Atari 2600 Black Screen Repair], Tynemouth Software; and [https://consolemods.org/wiki/Atari_2600:General_Troubleshooting ConsoleMods Wiki]. Source for the three-chip architecture (6507 CPU at 1.19 MHz, TIA, 6532 RIOT), the dirty-cartridge-contact cause of blank/corrupt screens, the 3.58 MHz crystal / TIA clock division, the RIOT socket contact fault, and the cold-solder reflow.</ref>
* '''Reflow the 6507, TIA and 6532 solder joints''' — cold or cracked joints there give a degraded or missing picture even when the chips themselves are good.<ref name="a2600">[https://retro64.altervista.org/blog/atari-2600-and-7800-repair-tales/ Atari 2600/7800 repair tales], Retro64; [http://blog.tynemouthsoftware.co.uk/2015/02/atari-2600-black-screen-repair.html Atari 2600 Black Screen Repair], Tynemouth Software; and [https://consolemods.org/wiki/Atari_2600:General_Troubleshooting ConsoleMods Wiki]. Source for the three-chip architecture (6507 CPU at 1.19 MHz, TIA, 6532 RIOT), the dirty-cartridge-contact cause of blank/corrupt screens, the 3.58 MHz crystal / TIA clock division, the RIOT socket contact fault, and the cold-solder reflow.</ref>

=== Socket and contact faults ===

Early 2600s used cheap IC sockets, and the '''6532 (RIOT)''' socket in particular develops contact problems (pin 22 is a documented offender). Reseat the socketed chips, and replace a bad socket rather than just cleaning it.<ref name="a2600">[https://retro64.altervista.org/blog/atari-2600-and-7800-repair-tales/ Atari 2600/7800 repair tales], Retro64; [http://blog.tynemouthsoftware.co.uk/2015/02/atari-2600-black-screen-repair.html Atari 2600 Black Screen Repair], Tynemouth Software; and [https://consolemods.org/wiki/Atari_2600:General_Troubleshooting ConsoleMods Wiki]. Source for the three-chip architecture (6507 CPU at 1.19 MHz, TIA, 6532 RIOT), the dirty-cartridge-contact cause of blank/corrupt screens, the 3.58 MHz crystal / TIA clock division, the RIOT socket contact fault, and the cold-solder reflow.</ref>

=== RF, switches and controllers ===

* '''No signal on the TV''': check the RF modulator, the channel 2/3 switch and the TV-type switch; a composite/AV modification is a common upgrade for a clean picture.
* '''Controller or console-switch faults''': the joysticks and the front switches are read through the 6532 — clean the switch contacts and the controller ports.