Editing Atari 2600 Troubleshooting Guide (section)

== Video Display Issues ==

=== Black Screen - No Display ===
'''Symptoms:''' TV shows black screen, may have sound

This is the most common Atari 2600 failure with multiple potential causes:

'''Diagnostic Flowchart:'''

# '''Verify sync signal present:'''
#* Analog TV: Screen appears "tuned" (fuzzy black, not static)
#* Digital TV: May show "No Signal" even with sync present
#* If no sync, proceed to TIA testing

# '''Test with known-good cartridge:'''
#* Try multiple cartridges
#* Clean cartridge contacts thoroughly
#* If one cartridge works, problem is cartridge-specific

# '''Check cartridge slot:'''
#* Inspect 24 pins for bent/pushed back contacts
#* Clean with isopropyl alcohol and credit card method
#* Verify plastic tabs present for dust cover activation

# '''Test TIA chip:'''
#* TIA generates all video and audio
#* Most common IC failure on 2600
#* Swap with known-good TIA or donor console
#* No substitute parts available

# '''Test RIOT chip:'''
#* Contains 128 bytes system RAM
#* Faulty RIOT causes no boot
#* Less common failure than TIA
#* Test by substitution only

# '''Test 6507 CPU:'''
#* Rarely fails but possible
#* Check for clock signal on pin 39 (3.58MHz)
#* Verify reset on pin 40 goes high after power on

=== Garbled/Scrambled Display ===
'''Symptoms:''' Game displays but with wrong colors, missing sprites, corruption

'''Causes and Solutions:'''

# '''Dirty cartridge contacts:'''
#* Most common cause
#* Clean thoroughly with alcohol
#* Use pencil eraser for stubborn oxidation

# '''Faulty RAM in RIOT:'''
#* 128 bytes internal RAM corrupted
#* Games may partially work
#* Replace RIOT chip

# '''Address/Data line issues:'''
#* Check continuity on all cartridge pins to CPU
#* Look for broken traces near cartridge slot
#* Repair with 30AWG wire jumpers

# '''Failing TIA:'''
#* Partial TIA failure causes specific artifacts
#* Missing colors: Color generation circuit failed
#* Missing sprites: Sprite registers corrupted
#* Rolling/tearing: Sync generation issues

=== Vertical Rolling ===
'''Symptoms:''' Picture rolls vertically, won't sync

'''Diagnostic Steps:'''
# Check vertical sync generation (TIA pin 2)
# Verify WSYNC operation (TIA register $02)
# Test with different TV/monitor
# Common with partially failed TIA

=== Horizontal Tearing/Jitter ===
'''Symptoms:''' Picture tears horizontally, unstable

'''Solutions:'''
# Check horizontal sync (TIA pin 3)
# Verify crystal oscillator: 3.579545 MHz
# Replace crystal if frequency incorrect
# Check for noise on power supply

=== Wrong Colors ===
'''Symptoms:''' Colors incorrect but game plays normally

'''Testing:'''
# PAL TIA in NTSC system or vice versa
# Check TIA part number:
#* C010444 = NTSC
#* C011903 = PAL
# Color adjustment pot on some models (not applicable to 2600)

=== Jail Bars (Vertical Lines) ===
'''Symptoms:''' Faint vertical lines through entire display

'''Causes:'''
# RF interference from digital circuits
# Insufficient power supply filtering
# Common on all 2600s to some degree

'''Mitigation:'''
# Add additional filtering capacitors
# Composite video modification eliminates issue
# Ensure RF shield properly grounded