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Commodore 64 & 128 Hardware Failure Cheat Sheet
See the original scan and C64 motherboard layout at the bottom of this page

Commodore Diagnostician II
By Ian Perry, Kyneton, Victoria 3444, Australia
Sept 1989

Symptomatic Chart Diagnosing
Faulty IC Components On
Commodore 64 &
Commodore 128


6510 Proc 6526 Complex Interface ADP 6581 Sound Interface Device 6567 VIC NTSC (6569 PAL) 82S100 Prog Logic Array 901226 Basic ROM 901227 Kernal ROM' 901225 Char ROM 8701 IC Clock Gen 2114 Color RAM 4164 Memory RAM Power Supply
Cursor jumps back to home position x x
Abnormal colors appear in the letters x x
Different characters are displayed, cursor is locked when turned on & off x x x
The 'RESTORE' key does not work x x
Cursor stops blinking when system warms up x
Keyboard does not operate correctly when system warms up x x x
Syntax error x x
Cursor disappears when cassette is plugged in x
Cassette runs extremely slow, the program see,ms to load but will not run x
Blank screen on power up x x x x x x x
Intermittent blank screen or graphics x x x x x
Powers up when 'PRESS PLAY ON TAPE' message and the display blinks x x
When 'RETURN' is pressed after a run command, cursor returns to home position x       x x x       x  
Poke command does not work x
Joystick does not operate correctly x
Unreadable letters appear on screen x x
Keyboard is unresponsive x
Graphic characters instead of letters are displayed x x x
'DEVICE NOT PRESENT' error is displayed, when disk is used x x
Disk drive continues to search when trying to load x x
Inconect screen color or no color at all x x x
Cassette does not save x
Flashing colors or blocks x x
Game cartridge does not function x x
User port doeS not function (eg. modem) x
No sound x
Missing notes x
Game paddles do not function x
Long programs do not lOad x x x
Unit completely dead (30 - 40% possibility PLA) x x x x x x
Wavy screen after system warms up x
'OUT OF MEMORY' error on power up x
After a few minutes, characters all over screen x x x x

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