So I bought this non working Pericom terminal which won't power up (shorted smoothing capacitors and burned out bridge rectifier) and also has a pretty 'terminal' case of screen 'cataracts'.
Have the rectifier and capacitors on order so decided to tackle the screen problem. This is caused by the ageing of the 'glue' that bonds a layer of protective glass to the CRT. It becomes opaque and starts to bubble - usually around the edges.