At the time we had a simple procedure at our Field Office to determine
if the CRT should be replaced or not. I don't recall if it was an official procedure
or something we came up locally. We set the T/B to the fastest sweep speed with
X10 Magnifier, Hold Off to max, Auto Trig and no input signal. If the trace could
be seen with Intensity set to max , even just quite dim, the CRT was considered OK.