Editing Commodore VIC-20 Troubleshooting Guide (section)

== IC failure reference ==
{| class="wikitable styled-table"
! IC !! Function !! Failure behaviour
|-
| MOS '''6502''' (40 pin) || CPU, executes KERNAL/BASIC || Black screen, no bus activity; may overheat
|-
| MOS '''6560/6561 VIC''' || Generates φ2, video, 3-voice audio || No video + no sound (total); or colour gone, rolling picture, silent audio
|-
| MOS '''6522 VIA × 2''' || Keyboard, joystick, IEC, timers, cassette || Dead keyboard, motor won’t run, “DEVICE NOT PRESENT”, stuck IRQ
|-
| '''SRAM''' 2114 / 6116 || 5 KB main + colour memory || Garbled text, random lock-ups, wrong colours
|-
| '''ROMs''' (BASIC / KERNAL / CHAR) || System firmware & font || Black screen (BASIC/KERNAL) or correct screen with wrong glyphs (CHAR)
|-
| 74LS logic (138, 245, 157 …) || Decode & bus buffers || Black/garbled screen, often one enable line missing
|}