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| 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 |