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VectorGlow
10th May 2009, 09:40 PM
Symptom: No sprites, only background visible. Also sometimes on power up the screen is white and game plays ?blind?.
Cure: Took ages to trace through things but determined that the fault lay with the smaller upper sub-board and noticed that there were no outputs on the 2148 at location 22A. Traced pin 11 back to various locations including pin 9 of the LS244 at 21D; found no input to, for example, pin 11 of the LS244 at 21D. Traced back pin 11 to pin 8 of the 74S08 at location 20D where it was found that pin 10 was inactive. Traced THIS back to pin 6 (tied to pin 2) of the 74S74 at location 15E and found that pin 7 was stuck low. (Note: snipping pin 6 of the 74S74 causes a white screen, while replacing the chip fixed both faults). Done!

egm110
28th July 2009, 10:37 PM
my pcp not work please help me i need schemmatics for repair tanks

VectorGlow
28th July 2009, 11:15 PM
There aren't any online schems for Twin Cobra I'm afraid. :(