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A dead set would act the same as an unpluged set. A shrunken raster can be caused by a power supply issue, and in some sets by horizontal issues (the horizontal output in addition to horizontally sweeping the CRT it also generates the 20KV HV, and a boosted B+ supply that is often used for part of the supply of the vertical, and sometimes other circuits).
So partial failure of either could drop the raster size down to the point of being objectionable to the owner.
Once one knows what to look, listen and smell for one becomes able to isolate the problem to 1 to 6 tubes and the parts arround them (in most cases) without takeing the back off. From experience I can say that this skill is a double edged sword allowing me to find and fix fault fast (when I'm thinking clearly), but it also makes it hard to watch TV as I end up constantly scrutinizing the most piciune details of the image constantly gauging the preformance of the circuits (unless I'm super lost in a good program).
I wish I could hand you a scenario that would require benching a set, but I've never worked on other people's sets before so I don't have a good idea of what jobs could be done in home easily.
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