Now you have confirmed that the problem of one horizontal line is in the vertical section. Next you use all your troubleshooting skill and your mighty test equipments to locate the fault in the vertical section. You are puzzle as after spending couple of hours you still could not locate the problem! You then search for schematic diagram for that model and still can’t find out the culprit. The scope waveform has some slight differences but you are not confirming because you do not have a similar equipment to compare the waveform. Let me tell you that if you have tried all your best in finding out the fault and you still could not locate the problem then i suggest you to use the meter’s continuity test to check the circuit track from point to point.
You wouldn’t know that it may have a hairline crack along the pathway and worst some crack may not be detected even using a magnifier glass. With the continuity test from point to point you will be very sure the line (circuit track) will not have problem. Do not overlook the continuity test as it could be very helpful for such a time as this.