[old_tv_nut]

No way you can cause a single phosphor dot to disappear. This is a manufacturing defect. Normal to have a small number of these. The maker would have a QC spec saying where on the screen they could appear, and how many, before it was considered a reject. For example, they might define a center circle where none were allowed, a larger radius allowing a certain number, and then the remaining area with a larger number allowed, plus perhaps an over-all total maximum. Don't recall if these numbers typically show in the published specs; they might be published for a professional monitor though not for the tube itself.