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From my own experience with a Blackstripe from Dec of '84 (and tips I've read on this forum), look for a couple of 2.2uF 50V electrolytic caps near a big 42 pin IC. These caps need to low be ESR and as they age, the ESR tends to go up and cause problems. As a temporary fix, since I didn't have the right cap, I used a 2uF film cap and it solved the roll issue. Another trick when working without a schematic, is do a google search on the ICs. The big 42 pin IC in my set is a TA644. Examining the data sheet shows pin 28 is connected to the vertical ramp capacitor, and the typical application drawing in the datasheet shows this pin connected to a 2.2uF cap.
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