Editing Atari 2600 Troubleshooting Guide (section)

== Component-Level Diagnostics ==

=== Testing Main ICs ===

'''6507 CPU (C010745):'''
# Check clock on pin 39: 1.19MHz square wave
# Verify reset on pin 40: High after power-on
# Monitor address bus activity: Pins 6-18
# Data bus activity: Pins 5, 7, 12, 14, 16, 18, 19, 21, 23

'''RIOT (C010750):'''
# Contains 128 bytes RAM ($80-$FF)
# I/O ports for controllers
# Timer functionality
# Test by substitution with known-good chip

'''TIA (C010444 NTSC / C011903 PAL):'''
# Generates all video and audio
# Most failure-prone chip
# No modern replacements available
# Donor console required for replacement

=== Using Diagnostic Cartridge ===

The Atari 2600 Diagnostic Cartridge performs automated tests:

# '''RAM test:''' Tests all 128 bytes in RIOT
# '''ROM test:''' Verifies cartridge ROM integrity
# '''TIA test:''' Checks video generation
# '''RIOT test:''' Tests I/O and timer functions
# '''CPU test:''' Basic instruction verification

Error codes displayed as:
* Smiley face: All tests passed
* Number: Specific component failure
* Common error codes:
** 1: RAM failure
** 2: ROM failure
** 3: TIA failure
** 4: RIOT failure
** 8: Collision detection failure

=== Chip Swapping Diagnosis ===

When diagnostic cartridge unavailable:

# '''Create minimal test setup:'''
#* Known-good power supply
#* Known-good cartridge
#* Direct connection to TV (bypass switch box)

# '''Systematic chip swapping:'''
#* Start with TIA (most common failure)
#* Then RIOT (second most common)
#* Finally CPU (rarely fails)

# '''Socket considerations:'''
#* Many chips are socketed on older models
#* Clean oxidation from pins and sockets
#* Check for bent pins when reinserting