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porchy
14th January 2010, 04:48 PM
Problem: Game would start, but controls were unresponsive and hung at certain point, plane even flew in a straight line in demo.

Fix: Checked the address lines on RAM (TMM2016) @ N10 + N11 with a scope, very weak signals on several lines. Desoldered, socketed and replaced. All working nicely again.

UPDATED:
Another 1942 board, another problem. Thought id update this one rather than start a new thread.

Problem: Screen bouncing left to right.

Fix: Suspected a sync issue. Signal looked ok on the scope but traced back from edge connector to a resistor (i think it is a 330ohm) which goes to pin 4 of a 74LS02 @ H9 (NOR gate). The inputs for pin 4 are pins 5 and 6. When I hit pin 6 with the scope, the screen screwed up and went blank. Followed this line back through pin 4 of an LS04 @ K4, pin 11 of an LS08 @ K9 and finally to pin 11 (output Y4) of an LS138 @ J4 (Decoder/Demultiplexer). When hitting input B of the LS138, the screen once again went blank, this came from an LS161 @ J3 (Fujitsu!). Replaced this little fella and picture is steady as a rock.

@lien_Zed
14th January 2010, 05:10 PM
excellent! top work. anther pcb saved :030: