Editing Amstrad CPC 464 Troubleshooting Guide (section)

=== Branch A &mdash; No display ===

# Verify '''5 V at J104''' with a multimeter. If absent, suspect the monitor 5 V supply (not the system unit). Try a stand-alone 5 V/2 A PSU.
# If 5 V present at J104, verify the '''DC cord''' (part 170316) and the system unit's internal +5 V at the power-input area.
# If +5 V is present on the planar but no display:
#: Candidate FRUs: '''Video connector J101''', '''DIN cable to monitor''', '''Gate Array IC116''', '''Z80A IC111''', '''CRTC IC108''', '''16 MHz crystal X101''', '''RAM bank IC117&ndash;IC124'''.
# Probe the 16 MHz crystal at X101 with an oscilloscope. If absent, the master clock is dead &mdash; the Gate Array generates a 4 MHz Z80 clock and 1 MHz CRTC/AY clock from this. Without it nothing happens.
# Probe Z80 pin 6 (clock input). If absent, the Gate Array clock divider is dead or the GA itself is dead. The 40007 GA (Ferranti) is the most common failure point on original-revision boards.