The picture is excellent when working, but once or twice during the evening the picture seems to break up. Just before or just after this occurs, the picture rolls upwards and the flyback
lines appear.-S. A. Whitmill (Andover, Hanti.). It would appear that a disturbance occurs in the vision strip which upsets
stages. This could be merely a poor valve base
contact, a dry joint, a faulty capacitor (decoupling) or even incorrect i.f. (sound rejector?) alignment.