The Commodore 64 Fixer

by Bill Dun, Cincinnati Commodore Computer Club

Note: this information is presented without warantee or gaurantee to it's reliability or effectiveness. Nor does it imply that these methods will work or are the only ones possible.

Reprinted from the Commodore Club of Rockford Newsletter - March 1993

Code	Check These	Code	Check These
A	6510	F	226
B	6526	G	227
C	6581	H	225
D	8587	I	8701
E	PLA	-

CHECK THESE									SYMPTOMS
6510	6526	6581	8587	PLA	226	227	225	8701	-
A									Cursor jumps back to the home position
				E					Abnormal colors appear in the letters
A			D						Different characters are displayed & cursor is locked
A			D			G			System does not re-set & RESTORE does not work
	B								Cursor disappears after warm up
					F				SYNTAX ERROR displays after warm up
A						G			Systems resets & long programs do not load
	B				F				Keyboard does not operate when warm
A			D		F			I	Blank screen on power up
A									No cursor displayed, intermittent screen
									On power up, PRESS PLAY ON TAPE, & display blinks X
A									On power up, the cursor does not work
					F				When return is pressed, the cursor goes to home position
					F				POKE command does not work
	B								Joystick does not operate correctly
	B			E	F		H		No character lettering is displayed
	B		D						Graphic characters instead of letters are displayed
	B				F				Power up message appears, but no cursor
A	B								Device not present when disk is used
	B								Disk drive continues to search, trying to load
			D	E					Incorrect screen colors or no color
	B								Keyboard does not work
					F				Flashing color or blocks
					F	G			Game cartridge does not work
				E					Unit dead - 40% possibility play
				E					User port does not function (ex. modem)
	B								No sound
	B								Missing notes
	B	C							Game paddles do not work

SYMPTOM	CHECK THESE
White band scrolls down the screen (60HZ hum)	Check p/sup & VR2 reg.
Wavy screen after warm up	check p/sup & 6587
Black band scrolls after warm up	Check p/sup & VR2 reg.
OUT OF MEMORY error on power up	Check RAMS 4146, U1-U12, U21-U24
Powers up w/graphic display & blinking cursor	Check U14
Powers up with all characters as blocks	Check U26
Unit completely dead	Check power supply
Characters are all over the screen & locks up	Check power supply

PLA CHIP IS AN 8SQ2S100

ROM CHIPS ARE

901226-01 (BASIC)
901227-01 (KERNAL)
901225-01 (CHARACTER)