Editing Commodore 64C Troubleshooting Guide (section)

== Display & Chime Diagnostics ==

The C64C lacks a startup chime, so video output is your primary indicator. Use the following table to interpret common power-on symptoms:

{| class="wikitable styled-table"
! Symptom !! Likely Cause !! Action
|-
| Black screen, no border || PLA, VIC-II, or CPU failure; no clock; bad ROM || Check voltages, swap VIC-II, PLA, CPU; test with Dead-Test cartridge
|-
| Blank screen with border || BASIC ROM failure || Swap BASIC ROM (U3)
|-
| Coloured border, garbage text || RAM or character ROM fault || Test RAM (U10–U17), swap character ROM (U5)
|-
| Solid white/grey screen || VIC-II alive, but no bus access || Check PLA, address lines, CPU
|-
| Rolling/distorted image || Wrong VIC-II or bad clock circuit || Confirm VIC-II type, check 8701/oscillator
|-
| No video, but power LED on || Dead VIC-II or missing 5 V/9 V || Confirm supply rails, swap VIC-II
|}

=== Minimal Boot Procedure ===
# Remove SID, both CIAs, and 4066 ICs (if socketed).
# Power up: if BASIC screen appears, one removed IC was dragging the bus.
# If still dead, proceed to chip substitution (see below).