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VectorGlow
10th May 2009, 09:09 PM
Symptom: Three horizontal lines of white pixels towards the bottom of the display (bottom board)
Diagnosis: Thought it was probably a video RAM problem but decided to see if the fault changed as the chips warmed up. Sure enough some of the pixels faded away so applied freezer spray to the suspects on the lower board. Sure enough the faded pixels came back good and strong when freezer spray was applied to the 6148 at location 4B. Tried piggy-backing a 2148 (I didn?t have any 6148?s) on top of that and that ?fixed? the fault, so removed the old 6148, popped in a socket and a new 2148
Cure: Replaced faulty 6148 RAM at location 4B

Symptom: All moving sprites are ?shredded? into vertical bars and data in one ?bar? is produced in the rest (bottom board)
Cure: Pin 10 stuck low on the LS283 at location 5E ? replaced

Symptom: Horizontal lines (about half a character high) throughout the background graphics
Cure: Bad output on pin 15 of the LS194 at 7K ? replaced