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Hi All,?

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My 2955B has a collapsed (smaller writing) 3rd line on the display screen.

I believe it has something to do with the vertical amplifier on the screen circuit. But only visible on the 3rd line from the top. This fault is intermittend, sometimes it is perfect and sometimes smaller.?

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Has anyone experienced this, and maybe have a possible idea where to start looking.?

I suspect? maybe a bad capacitor on the vertical amplifier?

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Regards Arthur?

Hi Arthur,

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I’ve seen similar a few times, in all cases it’s been a failing LOPT.?
Not sure if you’re aware, but the 2955 scans vertically, I.E. the scan coils are rotated through 90 degrees, so the vertical deflection is driven from the LOPT side of things. Even the manual confuses the vertical and horizontal adjustments.?
I’m not quite sure of the failure mechanism, but I’d guess one of the diodes in the rectifier stack or one of the windings starts breaking down at a particular voltage which corresponds to a particular vertical deflection, which in turn causes a hiccup in the vertical sweep.?

Cheers,

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Pete