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64 TROUBLESHOOTING GUIDE

SYMPTOM
POSSIBLE SOLUTION
Blank screen on power up. Check External Power Supply
U4 (KERNAL ROM), U17 (PLA)
U7 (6510 MPU), U3 (ROM)
U8 (7406 IC), U19 (VIC II)
U9-U12 (4164 RAM)
U21-U24 (4164 RAM)
BT2, CR4, VR1
Out of memory error on power up. Check U9-U12 (4164 RAM)
U21-U24 (4164 RAM)
**** USE DIAGNOSTIC TEST - DISK
No cursor displayed. Intermittent blank screen. Check U1, U15, U7
Check U2, U7
Powers up with graphics display and blinking cursor Check U14 (74LS258 IC)
Powers up with all the characters displayed as blocks. Check U26 (74LS373 IC)
Intermittent display. Check C88 (Possible Bad Connection)
Powers up with the 'PRESS PLAY ON TAPE' message and the display blanks Check U7 (6510 MPU)
R1 (Possible Bad Connection)
On power up the cursor lock up. Check U7 (6510 MPU)
U20 (556 IC)
When 'RETURN' is pressed after a run command, the cursor goes back to home position. Check U3 (ROM)
Poke command does not work. Check U3 (ROM)
Joystick does not operate correctly. Check U1, U28 (6526 CIA)
Wrong frequency. Check C70
No character lettering is displayed on the screen. Check U3 (ROM)
U2 (CIA)
Graphic characters instead of letters displayed. Check U19 (VIC II)
Power up message appears but no cursor. Check U1, U15, U7 and U4

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This page has been created by Sami Rautiainen.
Read the small print. Last updated September 05, 2020.