After looking at the video, and Mattis' description of the sweep method, I'm guessing a counter in the chain has gone bad. Assuming this uses a 5 x 7 character matrix, then there would be probably a divide by 6 for the scan across each character plus space between, then a counter for the number of characters per line, a counter for the 8 or 9 raster scan lines for each row, and then a counter for the number of rows. At least one of those counters might be counting too fast. Does the vertical just give one reset pulse, or does it give a pulse to bump the trace down the screen one scan line at a time? Also, a cap in the vertical sweep circuit may have gone bad, causing the vertical to move too
fast, as evidenced by sloping lines on the screen.

Just guessing from a distance.

Jon

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